Knowledge Class

Proteins

2012-01-17T21:19:00.000+05:00

Proteins are the main structural components of the cell. All proteins contain C, H, O and N. Some contain P, S, and few have Fe, I and Mg incorporated into the molecule.

Amino acids: Amino acids are the building blocks of proteins. Some other types of molecules may be attached to proteins e.g. nucleic acids, lipids and carbohydrates. There are many amino acids known to occur, but only 20 are commonly found in proteins. Plants re able to make all amino acids from simpler substances The amino acids are built on a common plan Each contains a carbon atom It is called alpha carbon, to this a hydrogen atom , an amino group - NH2, a Carboxyl group -COOH and a variable group known as - R group, are attached. The R group has a different structure in each of the 20 biologically important amino acids and determines their individual chemical properties.

general structure of amino acids

Chains of amino acids

Peptide Bond: How amino acids fit together? The bond formed to unite two amino acids is called peptide bond. It is between amino group of one amino acid and carboxyl group of another amino acid. Thus the bond is between C-N. The linkage of C=O and NH is called amide or peptide linkage. Water is removed in this process. The chain of amino acids joined by peptide bonds is called polypeptide chain.

Proteins have levels of structures: An analysis of protein shape shows that proteins can have up to four levels of structures (1) Primary structure (2) Secondary structure (3) Tertiary structure (4) Quaternary structure.

Primary structure

The primary structure of a protein is the sequence of amino acids joined by polypeptide bonds. In 1953 Fredric Sanger determined the amino acid sequence of hormone insulin. It was a laborious ten years task. Insulin is a small protein. The protein is constructed by two polypeptide chains of 21 and 30 amino acids. There is also a disulphide bridge between two cysteine of the smaller chain.

Secondary structure

The secondary structure of a protein comes about when the polypeptide takes a particular orientation in space. The two possible patterns of amino acids within a polypeptide are cc (alpha) helix structures, beta pleated sheet.

α (Alpha) helix: The polypeptide chain is loosely coiled in a regular spiral shape called an α -helix.

The twisting of the chain: There is a slightly negative charge on the oxygen and nitrogen and slightly positive charge on the hydrogen associated with a peptide bond. These charges make it possible for hydrogen bonding to occur between C = o of one amino acid and the N - H of another amino acid in a polypeptide. Hydrogen bonding between every fourth amino acid holds the spiral shapes of an helix. Thus amino acid at 1 would be bonded to amino acid 5, number 2 to number 6, and so on. The secondary structure is usually studied by technique of X-ray crystallography. In this process X-ray is passed through a purified crystal of protein, when this is done X-rays are scattered by the crystal and form a characteristic pattern which can be recorded on a photographic plate. Using mathematical technique, the structure of the protein can be inferred from the pattern it produces. X-ray diffraction data indicate that the helix makes a complete turn for every 3.6 amino acids.

Example of helix protein is keratin (found in hair, nails) wool, collagen (found in skin). 13- pleated sheet: In the 13 -pleated structure of proteins, the polypeptide chains are more extended and lie parallel with hydrogen bonding between chains. It is the main protein component of the silk.

Tertiary structure: Usually the polypeptide chain bends and folds extensively forming a precise compact globular shape called the tertiary structure of proteins. The structure is maintained by the interaction of ionic bonds, hydrogen and disulphide bonds as well as hydrophobic interaction e.g. myoglobin.

Quaternary structure: Many highly complex proteins consist of more than one polypeptide chains. The separate chains are held together by hydrophobic interaction of hydrogen and ionic bonds. This is known as quaternary structure. It can be more understandable by seeing the structure of hemoglobin. It is the oxygen carrying red pigment found in the red blood cells of vertebrates. It consists of four separate polypeptide chains of two types, namely two alpha and two beta chains. Each alpha contains 141 amino acids and each beta chain contains 146 amino acids.

Significance of Sequence of Amino acids: A protein molecule may have 51 to 3000 amino acids. All the amino acids must be in proper position in the polypeptide chain. If the proper site of even a single amino acid is changed, the normal structure and function of the protein is changed e.g. sickle cell anemia. Hemoglobin consists of two alpha and two beta chains. The fault occurs in the sixth amino acid in the beta chain. The glutamic acid of the normal hemoglobin is replaced by valine in the hemoglobin of a sickle cell.

Shapes of protein molecules: The shapes of protein molecules are in accordance with their function. Thus shape of protein molecules has a significant role. The shapes may be fibrous, globular and intermediate.

Fibrous: These proteins have long parallel polypeptide chains cross-linked at intervals forming long fibers or sheets. These have secondary structures physically tough and insoluble in water. These perform structural function e.g. collagen (tendons, bones, and connective tissue), myosin (in muscle), silk (Spider’s web) and keratin (hair, horn, nail, feathers).

Globular: Polypeptide chains are tightly folded to form spherical shape, having tertiary structure. These are the most important ones and are easily soluble. These form enzymes, antibodies, and some hormones e.g. insulin.

Intermediate: These proteins are intermediate in shape between globular and fibrous protein and are soluble e.g. fibrinogen which forms insoluble fibrin when blood clots.

Functions of proteins

Proteins play important functions in the living organisms. A brief account of functions of proteins is given as follows.

1. Proteins play an important role in membranes where they function as enzymes, receptors, and transport sites.

2. Proteins form the structural part in the organisms, such as collagen is the component of connective tissue of bones, tendons and cartilage. Keratin forms feathers, nails, hair and horn. Elastin forms elastic connective tissues in ligaments. Viral coat proteins wrap up the nucleic acid of virus.

3. Enzymes are proteins e.g. trypsin catalyses hydrolysis of proteins.

Some hormones like insulin, glucagon (a pancreatic hormone that raises blood sugar by promoting conversion of glycogen to glucose in the liver) and ACTH

4. (Adrenocorticotropic hormone secreted by anterior lobe of pituitary gland) are proteins which help to regulate glucose metabolism.

5. Respiratory pigment hemoglobin transports oxygen in vertebrate’s blood and myoglobin stores oxygen in muscles.

6. Some proteins are antibodies, fibrinogen and thrombin .have protective functions. Antibodies form complexes with foreign particles. Fibrinogen form fibrin in blood clotting. Thrombin takes part in blood clotting mechanism.

7. Protein fibers like actin and myosin take part in muscle contraction.

8. Ova albumen is egg white protein and casein is milk protein. Their function is storage.

9. Snake venom are enzymes and diphtheria toxin is made by diphtheria causing bacteria

Qatar Airways INTERNATIONAL

2012-01-17T00:48:00.000+05:00

Qatar Airways Company Q.C.S.C. operating as Qatar Airways, is the flag carrier of Qatar. Headquartered in the Qatar Airways Tower in Doha,it operates a hub-and-spoke network, linking over 100 international destinations from its base in Doha, using a fleet of over 100 aircraft.

Qatar Airways operates services across Africa, Central Asia, Europe, Far East, South Asia, Middle East, North America, South America and Oceania, and was named Airline of the Year 2011 at the Skytrax World Airline Awards.

Qatar Airways is currently undergoing a major expansion and is one of the fastest growing airlines in the world.

The airline employs more than 20,000 people. 14,000 employees work for the airline directly while the other 6,000 work in the airline's subsidiaries.

DELL - IT COMPANY

2012-01-14T21:19:00.000+05:00

Dell, Inc. (NASDAQ: DELL) is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest technological corporations in the world, employing more than 103,300 people worldwide. Dell is listed at number 41 in the Fortune 500 list.

Dell has grown by both increasing its customer base and through acquisitions since its inception; notable mergers and acquisitions including Alienware (2006) and Perot Systems (2009). As of 2009, the company sold personal computers, servers, data storage devices, network switches, software, and computer peripherals. Dell also sells HDTVs, cameras, printers, MP3 players and other electronics built by other manufacturers. The company is well known for its innovations in supply chain management and electronic commerce.

Fortune Magazine listed Dell as the sixth largest company in Texas by total revenue. It is the second largest non-oil company in Texas – behind AT&T – and the largest company in the Austin, Texas area.

World Bank

2012-01-13T20:58:00.001+05:00

The World Bank is an international financial institution that provides loans to developing countries for capital programs.

The World Bank's official goal is the reduction of poverty. By law all of its decisions must be guided by a commitment to promote foreign investment, international trade and facilitate capital investment.
The World Bank differs from the World Bank Group, in that the World Bank comprises only two institutions: the International Bank for Reconstruction and Development (IBRD) and the International (IDA), whereas the latter incorporates these two in addition to three more: International Finance Corporation (IFC), Multilateral Investment Guarantee Agency (MIGA), and International Centre for Settlement of Investment Disputes(ICSID).

IMPORTANCE OF CARBON

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Carbon is an element that is found in all organic molecules. The term organic means living. Carbon has the atomic number 6 and each atom of carbon has two electrons in its first shell and four electrons in its second shell. Thus each atom has four electrons which can be shared allowing four covalent bonds to be formed, with other - atoms. The other atoms include hydrogen oxygen and nitrogen atoms and additional carbon atoms. The valency of carbon is four. Here carbon has formed four simple bonds with hydrogen.

Multiple bonds: Carbon can form double bonds with itself, C = C. In fact, carbon, oxygen and nitrogen can all form strong multiple bonds.

In a saturated carbon compounds all carbon - carbon bonds are single (C-C). Compounds containing double or triple carbon (C=C, CC) carbon bonds are called unsaturated. Carbon forms chains of various lengths and shapes or the size of the organic molecule is determined by the number of carbon atoms present. The chemistry of organic molecule is determined by the elements and chemical groups attached to the carbon atoms and how much saturated the carbon skeleton is. Shape of the organic molecule is determined by the geometry of the bonds of carbon. The C.- H bonds is a potential source of energy. Energy may be released when hydrogen atoms are removed in an oxidation reduction process. Some of the’ molecules formed by carbon in combination of other atoms are so unstable that they last for only the briefest time and then break down, releasing energy, e.g. ATP. In other cases the molecules built with carbon skeletons may be so stable that they hardly react at all, and are so big that they cannot dissolve in water. Such compounds make up the wood of trees. Because of these special properties and reactions of carbon atom, we can almost guess the answer to the question “Could there be life without carbon?”

CONDENSATION AND HYDROLYSIS

2012-01-10T15:27:00.000+05:00

During condensation, when two monomers join, a hydroxyl (-OH) group is removed from one monomer and a hydrogen (-H) is removed from the other. Water is given off during a condensation reaction. Condensation involves a dehydration synthesis because water is removed (dehydration) and bond is made (synthesis). Condensation does not take place unless the proper enzyme is present and the monomers are in an activated energy-rich form. Polymers are broken down by hydrolysis, which is essentially the reverse of condensation. Water is added during hydration, an OH group from water attaches to the other monomer. Hydration involves a hydrolysis reaction because water is used to break a bond. Again, the proper enzyme is required.

(a) In cells, synthesis often occurs when monomers are joined by condensation (removal of H₂O).

(b) Hydrolysis occurs when the monomers in a polymer separate after the addition of H₂O.

WATER

2012-01-09T23:04:00.000+05:00

As we have already seen that life first originated in water, so no life can exist on the earth without water. All living things are composed of 70% - 90% water. Water provides an environment for the organisms that live in it. Water is an inorganic substance as carbon is absent in H-O-H.

Polar molecule: The oxygen of water contains a negative charge and its hydrogen contains a positive charge, so water molecules are called polar molecules. As a result, the oxygen atom tends to attract the single electron of the hydrogen atom.

Biological importance of water

The water content varies from 65 to 90 percent in different organisms. Human tissues contain about 20% water in bone cells and 85% in brain cells.

Importance of Hydrogen bond in water: A hydrogen bond is much weaker than a covalent bond within a water molecule, but taken together, hydrogen bonds cause water molecules to cling together. Without hydrogen bonding between molecules, water would boil at 80°C and freeze at 100°C, making life impossible. But because of hydrogen bonding, water is a liquid at temperature suitable for life. It boils at 100°C and freezes at 0°C.

Solvent properties: Water is an excellent solvent for polar substances. These include ionic substances like salts which have charged particles i.e. ions and some non-ionic substance like sugar having polar group i.e. slightly negative hydroxyl group (-OH). On contact with water, the ions and the polar groups are surrounded by water molecules which separate the ions or molecules from each other. This is what happens when a substance dissolves in water. Once a substance is in solution, its molecule or ions can move freely, thus making it chemically more reactive than if it were solid. Thus, in the majority of the cells chemical reactions take place in aqueous solutions. Non-polar molecules are hydrophobic. Such hydrophobic interaction is important in the formation of membrane and helps to determine the three dimensional structure of many protein molecules and nucleic acids etc. Water’s solvent properties also mean that it acts as a transport medium e.g. blood and excretory system etc.

High heat capacity: Water has high heat capacity, i.e. a large increase in heat energy results - in a relatively small rise in temperature. The specific heat capacity of water the number of calories required to raise the temperature of 1 g of water from 15 to 16°C, is 1.0. The many hydrogen bonds that link water molecules help water to absorb heat without a great change in temperature and when water cools down, heat is released. However water holds heat and its temperature falls more slowly then other liquids. The property of water is important not only for aquatic organisms but also for all living things. Water protects organisms from rapid temperature change and helps them to maintain their normal internal temperature.

High heat of vaporization: It is expressed as calories absorbed per gram of water vaporized. The specific heat of vaporization of water is 574 k cal/kg. Evaporation of 2m1 out of one liter of water lowers the temperature of remaining 998 ml by l °C. Hydrogen bonds must be broken to change water to steam. For this, a large amount of heat is needed for evaporation. This property of water helps to moderate the temperature of Earth. It also gives animals in hot environment an efficient way to release heat. When an animal sweats its body heat is used to vaporize the sweat, thus cooling the animal.

High heat of fusion: Having high heat capacity, water requires relatively large amount of heat to thaw. Likewise liquid, water must lose a relatively large amount of heat to freeze. Contents of cells and their environment are therefore less likely to freeze.

Density and freezing properties: As water cools down, the molecules come closer together and water expands as it freezes. The density of water decreases below 4°C and ice therefore tends to float, as ice is less dense than liquid water. Water always freezes from the top down. When a body of water freezes on the surface, the ice acts as an insulator to prevent the water below it from freezing. This protects many aquatic organisms so that they can survive in winter.

Water molecules are cohesive and adhesive: Cohesion is the force whereby individual molecules stick together. The water molecules cling together because of hydrogen bonding. Because of cohesion water flows freely. Thus water is an excellent transport agent. They adhere to surface, particularly polar surfaces, therefore water exhibits adhesion. Cohesion and adhesion both contribute to the transport of water in plants.

High surface tension: At the surface of water a force called surface tension exists between the molecules as a result of cohesive forces between the molecules. These cohesive forces are due to hydrogen bonds. A water strider can even walk on the surface of a pond without breaking the surface of water.

Water as a reagent: Water is biologically significant as an essential metabolite, that is, it participates in chemical reactions of metabolism e.g. as a source of hydrogen in photosynthesis, and is used in hydrolysis reaction.

Water ionizes: When water ionizes, it releases an equal number of hydrogen ions (H) and hydroxide ion (OH).

H-C-H à H+OH

This reaction is reversible but equilibrium is maintained at 25°C. The H and 0H ion affect and take part in many of the reactions that occur in cells, e.g. it helps to maintain or change the pH of the medium.

INTRODUCTION TO BIOCHEMISTRY

2012-01-08T20:25:00.001+05:00

The study of the chemical compounds and the chemical processes in
living organisms is called biochemistry. It plays an important role in the
expansion of biological knowledge. It gives us the understanding that how
does the biological system work. The science of biochemistry is applied in
agriculture, medicine including the whole pharmaceutical industry and food
industry. Many of the recent developments in biology like genetic
engineering, biotechnology and molecular approach to genetic disease is
due to the science of biochemistry. Biochemistry is also one of the unifying
themes in biology. There are different biochemical processes like
photosynthesis, digestion, respiration, excretion and muscle contraction. All
these chemical processes take place in a cell. These chemical processes are
maintained with high degree of organization. Metabolism is the sum of all
chemical processes taking place in the cell. It consists of two processes
anabolism and catabolism. Those reactions in which simple substances
are combined to form complex substances are called anabolic reactions.
These reactions need energy. Those reactions in which complex molecules
are broken down into simpler ones, with the release of energy are called
catabolic reactions.

Chemical composition of cell

All organisms consist of cells. The structure and functions of cells
depend on the various biochemicals which form the cells. Water forms 70%
of a typical mammalian cell. It is present throughout the cell. Water dissolves,
suspends, and ionizes materials, helps to regulate temperature of the cell.
Electrolytes are present throughout the cell. The function of the electrolytes
is to establish osmotic gradients, pH and membrane potential. Proteins are
present in the membranes, cytoskeleton, ribosomes and enzymes of the
cells. The function of the proteins is to provide structure, strength,
contractility, catalytic activity and buffering capacity to the cells.

Lipids are present on the membranes of Golgi complex and inclusion

of the cell. Lipids provide a reserved energy source, shape, protect and

insulate the cells. Carbohydrates are present in the inclusions of the cells and

provide fuel for the metabolic activities of the cell. The nucleic acid DNA is

present in the nucleus, chromosome and gene. It controls the cell activity.

The nucleic acid RNA is present in the nucleoplasm and cytoplasm. It

transmits genetic information and transports amino acids. Vitamins and

minerals are present as trace elements in cytoplasm and nucleus. Vitamins

work with enzymes in metabolism. Minerals are essential for a normal

metabolism, involved in osmotic balance and add strength to buffer. The 16

elements and a few others, which occur in particular organisms are called

bioelements, in the living body only six bioelements are present for 90% of

the mass.

Relationship between structure and function of molecules

Small molecules

Carbon chains make up the skeleton or backbone of organic molecules.

Functional groups, which cluster certain atoms that always behave in a

certain way, can be attached to the carbon chain. Functional groups also help

-to determine the characteristics of organic molecules. The small organic

molecules are in living things i.e., sugar, fatty acids, amino acids and

nucleosides all have a carbon backbone and in addition, they often have one or more of the functional groups.

Large organic molecules .

Each of the small molecules can be a unit of a large organic molecule
often· called a macromolecule. A unit is called monomer and the
macromolecule is called polymer (GK-polys, many meros, part). Cells
contain only four classes of macromolecules e.g. polysaccharides, lipids,
proteins and nucleic acids. These macromolecules still have great variety
and therefore play different roles in cells.

THE IMMUNE SYSTEM

2011-12-23T11:17:00.000+05:00

Immunity is defined as ‘the capacity to recognize the intrusion or material foreign to the body and to mobilize cells and cell products to help remove that particular sort of foreign material with greater speed and effectiveness.

In this section we shall be confining our attention to the immune response. This is the second line of defense after the phagocytes which, according to the above definitions also part of the immune system. The immune response is the production of antibodies in response to antigens. Each antigen is recognized by a specific antibody.

Antibodies, Antigens, B-cells and T-cells

An antibody is a molecule that is synthesized by an animal in response to the presence of foreign substances knows as antigens. Each antibody is a protein molecule called an immunoglobulin.

An antibody is a molecule which can cause antibody formation. All cells possess antigens in their cell membrane surface which act as markers, enabling cells to recognize each other. Antigens are usually proteins or glycoproteins, that is, proteins with a carbohydrate tail, although almost any complex molecule can be antigen. The body can distinguish its own antigens (self) from foreign antigens (non-self) and normally only makes antibodies against non-self antigens. Microorganisms carry antigens on their surfaces.

Two systems of immunity have been developed by mammals, a cell mediated immune response and a humoral immune response. The two systems involve the development of two types of lymphocytes, the T and B cells. Both types arise from precursor cells in the bone marrow.

Cell-mediated response: T Cells attack the (i) Cells that have become infected by a microorganism, most commonly a virus. (ii)Transplanted organs and tissues. (iii) Cancer-causing cells.

The whole cell is involved in the attack, so this type of immunity is described as cell-mediated immunity. T cells do not release antibodies.

Humoral Response: B cells release antibodies into the blood plasma, tissue fluid and lymph. As the antibodies are released into fluids and the attack on the microorganisms takes place in the fluid, this type of immunity is described as humoral (‘humor’ means fluid). The antibodies of B cells attack bacteria and some viruses.

The Immune System Has a Memory: There are two types of B cells namely memory cells and effecter cells (meaning they carry out the response). Effecter cells are also known as plasma cells. These secrete huge numbers of antibody molecules into the blood, tissue fluid and lymph. Effecter cells live for only a few days. The memory cells survive for long periods of time and enable a rapid response to be made to any future infection.

The memory cells are important if a second infection of an antigen occurs. The population of memory cells is much larger than the original population of B cells from which they came. Therefore the response to the second infection, called the secondary response, is much more rapid and is also greater than the primary response to the original infection. The primary response may not be rapid enough to prevent a person suffering from an infection, but if that person survives, they will rarely suffer from it again because of the greater secondary response. With each exposure, the response gets more efficient. This is the basis of vaccination (and booster doses).

Types of Immunity: Immunity may be described as active or passive. Both types may be acquired naturally or artificially. Providing immunity artificially is called Immunization.

Natural Active Immunity: This is the kind of immunity which is obtained as a result of an infection. The body manufactures its own antibodies when exposed to an infectious agent. Because memory cells, produced on exposure to the first infection, are able to stimulate the production of massive quantities of antibody when exposed to the same antigen again, this type o immunity is most effective and generally persists for a long time, sometimes even for life.

Artificial Active Immunity (Vaccination): This is achieved by injecting (or less commonly administering orally) small amounts of antigen, called the vaccine, into the body of an individual. The process is called vaccination. The antigen stimulates the body to manufacture antibodies against the antigen. Often a second, booster injection is given and this stimulates a much quicker production of antibody which is long lasting and which protects the individual from the disease for a considerable time. Several types of vaccine are currently in use.

(a) Toxoids: Toxins (poisons) produced by tetanus and diphtheria bacteria are detoxified with formaldehyde, their antigen properties remain. Therefore vaccination with the toxoid will stimulate antibody production without producing symptoms of the disease.

(b) Killed organisms: Some dead viruses and bacteria are able to provoke a normal antibody response and are used for immunization purposes. An example is the flu vaccine which contains dead flu viruses.

(c) Live Vaccines’ (attenuated organisms): An attenuated organism is one which has been crippled’ in some way so that it cannot cause a disease. Often it can only grow and multiply slowly. Attenuated vaccines for the bacterial disease tuberculosis (TB), and for measles, mumps, rubella (German measles) and polio are in general use.

(d) Smallpox: It is now extinct; a live virus vaccine was used.

(e) New Vaccines: New approaches to vaccine design are now possible using modern techniques of molecular biology and genetic engineering. An alternative approach is to synthesize antigen artificially from amino acids, once their amino acid sequences are known.

Passive Immunity

In passive immunity antibodies from one individual are passed into another individual. They give immediate protection, unlike active immunity which takes a few days or weeks to build up. However, it only provides protection against infection for a few weeks, for the antibodies are broken down by the body’s natural processes, so their number slowly fall and protection is lost.

Natural Passive Immunity

Passive immunity may be gained naturally. For example, antibodies from a mother can cross the placenta and enter her fetus. In this way they provide protection for the baby until its own immune system is fully functional. Passive immunity may also be provided by colostrums, the first secretion of the mammary glands. The baby absorbs the antibodies through its gut.

Artificial Passive Immunity

Here antibodies which have been formed in one individual are extracted and then injected into the blood of another individual which may or may not be of the same species. They can be used for Immediate protection if a person has been; or is likely to be, exposed to a particular disease. For example, specific antibodies used for combating tetanus and diphtheria used to be cultured in horses and injected into humans. Only antibodies of human origin are now used for humans. Antibodies against rabies and some snake venoms are also available. Antibodies against the human rhesus blood group antigen are used for some rhesus.

THE LYMPHATIC SYSTEM

2011-12-23T10:29:00.001+05:00

Lymph Capillaries: The lymph vascular system originates as lymph capillaries. These are small vessels occur in the tissues of almost all organs. They are blind- end’ tubes, in that they have no entrance at the end residing in interstitial regions; the only opening is one that merges with the larger lymph vessels. The lymph capillary walls consist of only a single layer of endothelial cells. They seem to be permeable to all substances dissolved in the interstitial fluid.

Lymph: The composition of lymph is similar to that of blood. Lymph contains water, some plasma, proteins, electrolytes and lymphocytes, but it lacks RBCs, platelets and most of the blood proteins. Lymph is derived from the fluid portion of the blood that passes from the arterial ends of capillaries out into the spaces around the cells. The fluid lymph surrounds and bathes the cells of the body.

Lymph Nodes: Are located at intervals along lymph vessels. All lymph trickles through at least one of these nodes before being delivered to the blood stream. Lymph nodes are especially present in the neck, near the arm pits and in the groin area.

Structure: Each node has an outer capsule of fibrous connective tissue. Partitions from this capsule extend into the node itself, the spaces between are packed with lymphocytes and plasma. The node produces lymphocytes, and antibodies for the defense of the body.

Cause of Flow: The flow of lymph in the lymph vessel is brought about by the contraction and relaxation of the skeletal muscles and the breathing movement. The- direction of movement towards the main trunk and the back flow is prevented by valves present in the major vessels.

The two main lymphatic ducts are (i) Thoracic duct (ii) Right lymphatic duct

i. Thoracic duct: The lymphatic vessels of the legs join to those from the alimentary canal to form the thoracic duct. This empties lymph into the left subclavian vein.

ii. Right lymphatic duct: The right lymphatic duct drains lymph back into the blood stream via the right subclavian vein.

iii. Lymphoid Organs: It includes lump nodes, spleen, thymus (an endocrine gland), tonsils and patches of lymphoid tissue in the small intestine.

Functions:

(a) In an average person about three liters more fluid leaves the blood capillaries than is reabsorbed by them each day. It returns this excess fluid and its dissolved proteins and other substances to the blood.

(b) The lacteals of villi absorb large fat globules, which are released by interstitial cells after the products of digestion of fats are absorbed. After a fatty meal these fat globules may make up 1% of the lymph.

(c) The lymphatic system helps defend the body against foreign invaders. Lymph nodes have lymphocytes and macrophages that destroy the bacteria and viruses. The painful swelling of lymph nodes in corsair diseases (mumps is an extreme example) is largely a result of the accumulation of dead lymphocytes and macrophages.

(d) Just as the lymph nodes filler lymph, the spleen filters blood, exposing it to macrophages and lymphocytes that destroy foreign particles and aged red blood cells.

CARDIOVASCULAR DSORDERS

2011-12-04T14:39:00.000+05:00

A cardiovascular disorder (CVD) is the leading cause of untimely death in man.

1. Leukemia

It is characterized by uncontrolled production of leukocytes. As a result number of abnormal WBC5 greatly increases in the circulating blood. This is caused by a cancerous mutation of a myelogenous or lymphogenous cell. Myelogenous cells or bone marrow cells are in the bone marrow and may spread throughout the body, so that WBC is produced in many other organs. This WBC is not completely differentiated and so is defective.

Types of Leukemia: Leukemia are of different types depending upon the type of white blood cells, which are undifferentiated and being produced at a faster than normal rate. These may be neutrophilic leukemia, eosinophilic leukemia, basophilic leukemia, monocytic or lymphocytic leukemia, hairy cell leukemia. Leukemia is a serious disorder and the victim needs change of blood regularly. It can be cured by bone marrow transplant which in most cases effective, but a very expensive treatment. The ratio of occurrence is 8% in males and 7% in females. Leukemia patients are anemic, suffer from brain hemorrhage, and there is insufficient body defense mechanisms.

2. Thalassemia

The word thalassemia consists of two Greek words Thallassa, the sea, haema, blood. It is also called Cooley’s anaemia after the name of Thomas B. Cooley, an American pediatrician (the physician who treats children).

The thalassemia syndromes are a heterogeneous group of disorders. It is transmitted genetically. It is characterized by lack of or depressed synthesis of either the alpha or beta globin chain of haemoglobin. It is characterized by the presence of microcytes by spleenomegal i.e. enlargement of spleen and by changes in the bones and skin, and severe anaemia.

This disease is more common in Mediterranean countries and parts of Africa and Southeast Asia. It can be cured by bone marrow transplant which is very expensive and does not give 100% cure rate. Haemoglobin molecule in most cases does not have beta chain instead of it F (Foetal) haemoglobin chain is present.

3. Edema

The term edema means increased fluid in the interstitial tissue spaces. The excess of fluid may be inside or outside the cells. The intracellular edema is caused by osmosis of water into the cell. The extra-cellular edema is caused by:

(a) Abnormal leakage of fluid from the blood capillaries or failure of the lymphatic system to return from the interstitial fluid.

(b) Renal retention of sodium and water are clearly contributory factor of edema. Edema may occur at different sites e.g. subcutaneous edema, and pulmonary edema. Edema of the brain may be localized to sites of injury. Severe generalized edema is called anasarca.

Edema disturbs the exchange and concentration of minerals and ions in the blood and body cells. It affects blood pressure, increased heart beat etc. Pulmonary edema can cause death by interfering with normal ventilatory function. Brain edema is serious and can be rapidly fatal. )

4. Artificial Pace Maker

Sino- atrial node (SA node) is called a pace maker. It is responsible for initiating the impulses which trigger the heart beat rate. If there is some block in the flow of the electrical impulses or if the impulses initiated by SA node are weak it may lead to death of a person. So an artificial pace maker is used for the SA node to excite the heart. The artificial pace maker is battery operated. For example a four volt pace maker may be implanted in the flesh under the arm. It emits electric impulses 72 times a minute. A plastic coated wire carries the impulse through a vein to the right atrium, where its special tip is embedded in the heart’s pace maker.

Or if AV pathway is blocked the electrodes of artificial pacemaker are attached to the ventricle. Then this pacemaker provides continued rhythmic impulses that take over the control of the ventricles.

5. Blue Babies

The placenta provides the means by which the foetus obtains oxygen. At birth important changes take place in the circulation, associated with the fact that the respiratory function of the placenta is taken over by the lungs. In the foetus the umbilical vein conveys oxygenated blood to the posterior vena cava where it enters the right atrium of the heart. The lungs are functionless and most of the blood bypass them by flowing through the foramen ovule, a hole which, in fact, connects the right and left atria, and the ductus arteriosus, a vessel linking the pulmonary artery with the aorta. As a result of various pressure changes and nervous reflexes triggered principally by the rise in the partial pressure of oxygen in the blood when the baby takes its first breath, the foramen ovule and ductus arteriosus close soon after birth. The result is that from now on all the blood returning to the right atrium is sent to the lungs. Failure of the foramen ovule and or ducts arteries to close results in a ‘blue baby; a proportion of the blood continues to bypass the lungs, resulting in inadequate oxygenation of the tissues. Thus mixed blood is supplied to the body of new born babies resulting in the blueness of the skin i.e. cyanosis, thus the name “blue babies.”

6. Hypertension

Hypertension is a condition of high blood pressure. Prolonged high blood pressure damages the lining of the blood vessels and due to continuous strain imposed on the heart leads to weakening heart muscles. As a result efficiency of pumping action of the heart declines. It needs more oxygen to pump blood. Blood may then be retained in the heart and lungs, and often leads to fatal condition called congestive heart failure.

It has been shown that men under the age of 50 years with a blood pressure of 170/100 are twice likely to die of coronary heart disease as men with normal blood pressure of about 120/80. High blood pressure itself is associated with a number of factors including stress, obesity, smoking, drinking alcohol and lack of exercise. There is also a genetic predisposition in some people. Some of these factors can obviously be avoided by changes in life style.

Drugs known as B -blockers can be used to reduce hypertension. Hypertension is sometimes called as silent killer because it may not be detected until stroke or heart attack occurs.

7. Thrombus Formation and Hypertension: A clot on the inner wall of a blood vessel is called a thrombus. A thrombus can even block blood flow through a vessel or it can break loose from the vessel wall and be carried through the circulatory system. Such a free swimming clot is called an embolus (plural: emboli). Thrombosis is the formation of thrombus. In western civilization, thromboembolism is a leading cause of death.

Cause of Thrombus Formation:

(a) Irritation or infection of leading blood vessel.

(b) Reduced rate of blood flow due to long period of inactivity.

8. Atherosclerosis

Arthrosclerosis comes form two Greek words athere, porride, skeleoris, hardening. It is coexisting Atheroma and arteriosclerosis. Atherosclerosis is an arterial disease. This condition involves the formation of soft masses of fatty material in blood vessel linings. These fatty masses called contain large quantities of cholesterol. They often form in arteries, making the arterial lining much rougher than normal. These roughening tend to promote thrombus formation and leads problem with embolism. A plaque develops; it decreases the diameter of the blood vessel and impedes blood flow. The formation of calcium deposits in the plaque and degenerative change in the arterial wall lead to hardening of the artery Hardened. i.e., sclerotic arteries have lost their elasticity and are thus susceptible to rupture.

9. Heart Attack (Myocardial infarction)

Plaque also can break loose and circulate until it blocks a small blood vessel or its rough surfaces cause formation of a clot that blocks a vessel. This is especially devastating if the blocked vessel is one of the coronary arteries of the heart. The portion of the heart muscle denied of a blood supply lack of oxygen dies, and said to be infarction. The whole process is called myocra (heart muscle) infarction due to thromboembolism.

Angina Pectoris: If a coronary artery becomes partially blocked, the individual may suffer from angina pectoris (literally means chest pain) characterized by chest pains and or a radial pain in the left arm. Nitroglycerin or related drugs dilate blood vessels and help relieve the pain.

Precaution:

(a) Avoid too much food especially rich in cholesterol.

(b) Maintain normal body weight.

(d) Do not smoke.

(e) Observe Islamic way of life.

10. Stroke

Stroke, heart attack and aneurysm (abnormal dilation of blood vessel) are associated with hypertension and Atherosclerosis. A cardiovascular accident (CVA), also called a stroke or cerebral infarction, often results when a small cranial (brain) arteriole bursts or is blocked by an embolus.

Stroke causes necrosis or death of the surrounding neural tissues owing to lack of oxygen. The effect of a stroke depends on how severe the damage is and where in the brain the stroke occurs.

11. Haemorrhage

Blood loss is termed as Haemorrhage. When a small cranial arteriole bursts it is called brain Haemorrhage. It is caused when the wall of the arteries become hard and lose its elasticity and by high blood pressure.

Precaution:

(a) Blood pressure must be controlled within normal limits i.e. normal blood pressure must be maintained.

(b) Do not become overweight.

(d) Do regular exercise.

(e) Avoid stress and tension.

It is not a closed circulatory system, nor does it have a pump. It is made up of a network of thin walled vessels that carry a clear fluid called lymph.

BLOOD PRESSURE

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Blood pressure is the force exerted by the blood on the inner walls of the blood vessels. It is different in the different blood vessels.

Arterial blood pressure depends on the volume of blood in the arteries and the elasticity of the arterial walls and on the rate of the heart beat. The pressure is greatest in the large arteries leaving the heart, and gradually falls in the arterioles. It is lower in the capillaries and still lower in the veins.

Systolic Pressure: When the ventricles of the heart contract the arterial blood pressure is the highest. It is called systolic pressure.

Diastolic Pressure: When the ventricles of the heart relax, the arterial blood pressure is the lowest. It is called diastolic pressure.

Measuring Blood Pressure: The instrument used for measuring blood pressure is called sphygmomanometer. The instrument consists of an inflatable cuff, a rubber bulb and a column of mercury. The hollow cuff is wrapped around the upper arm and inflated to a pressure above the systolic pressure (the tightened cuff closes the arteries in the upper arm and prevents blood from flowing into the lower arm). A stethoscope is placed over the artery just below the cuff, and the pressure in the cuff is slowly released until the arterial pressure is greater than the pressure of the cuff.

At that point, a recognizable sound can be heard through the stethoscope. This sound signals the high-velocity release of blood, and the figure on the mercury column at which it occurs represents the systolic blood pressure.

When the cuff pressure is lowered further, a louder sound is heard, and then the sound gradually becomes softer. When the sound stops altogether, the diastolic blood pressure is noted on the column.

The absence of sound indicates a free flowing gush of blood through the open artery. The blood leaving the ventricles and entering the aorta and the pulmonary artery is under considerable pressure, where it normally reaches to 140mm of the mercury.

Variations in Blood Flow: The flow of blood also varies according to the conditions such as exercises, after eating and when the body is hot or cold. It also varies according to the need of the organs. Steady flow of blood is maintained to heart and brain.

Rate of Blood Flow

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Arteries: It is highest in aorta-400- 500 mm per second, decreasing along the arterial system.

Capillaries: It is greatly reduced in the capillaries, about 150 mm per second. The main reason for this is that cross sectional area of the capillaries is smaller than the large arteries; therefore there is decrease in the rate of blood flow. The slow rate of blood flow in the capillaries is of advantage in allowing adequate time for exchange of nutrients, hormone and metabolic wastes between the capillaries and tissues.

Veins: The larger veins have an over all larger total cross- sectional area, therefore, there is an increased rate of flow.

Pulmonary Artery: It arises from the superior surface of the right ventricle and immediately divides into right and left pulmonary arteries, going to the corresponding lung. These arteries carry deoxygenated blood.

Portal System: When a vein breaks up into capillaries it is called a portal vein. The veins coming from the alimentary canal, pancreas, spleen etc, join up to form a portal vein which enters the liver and breaks up into capillaries. The excess of glucose is filtered out through the walls of the capillaries into the hepatic cells where it is converted into glycogen and stored in them. The capillaries reunite to form the hepatic veins which open into the inferior vena cava.

The portal vein differs from other veins in that the blood it carries from the tissues pass through a second capillary network in the liver before it enters the inferior vena cava. The portal veins and its branches constitute the portal system.

Flow of Blood in the Vein

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As the blood pressure in the veins is comparatively lower, so the flow of blood in the veins is helped by gravity, semilunar valve and muscular contraction.

The Blood Vessels

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Blood vessels are named according to their structure and function.

Vessels carrying blood away from the heart are' called arteries. These branches into smaller arteries called arterioles. The arterioles divide many times into microscopic capillaries, which are 'located among the cells of nearly all the body tissues. Within the organ or tissue the capillaries reunite formingVenules. The venulesjoin toformveins.

Arteries: Arteries oxygenated blood except the pulmonary arteries which carry deoxygenated blood. Arteries are pink in colour and are situated within the muscles. Arteries vary in size. Aorta is 23 mm and arterioles are about 0.2 mm in diameter. Each artery consists of three layers:

1) Tunica externa: It is the external layer of fibrous connective tissue having collagen (a protein) fibres.
Tunica media is the middle layer of smooth muscles and elastic fibers. Tunica intima is the inner layer of squamous endothelium.

2) The middle layer is important to withstand higher pressure during ventricular systole. In the arterioles there are more circular muscles than the elastic tissue. The contraction of the circular smooth muscles of the arteries is under the control of nervous and endocrine system. When stimulated the muscles contracts, constricting the arteriole i.e, vasoconstriction and reducing the flow of blood in them.

When the muscles are relaxed and there is vasodilatation of the arterioles more blood flows in the arterioles.

Capillaries are microscopic one celled thick blood vessels. A capillary consists of a single layer of endothelial cells. Their number is highest in the regions where 'most of the metabolic activities are taking place. The average diameter of capillaries is 7 to 10 microns, just about that of single red blood cell. Hence blood cells move through the capillaries in a single row.

Exchange of gasses, nutrients, wastes and hormones between the blood of
the capillaries and various cells and tissues occur by diffusion and active
transport. The number of capillaries which arise from a single arteriole is
sufficiently great and the total cross sectional area available for the flow of the
blood is increased.

Veins: The blood vessels that bring blood back to the heart are called veins.
A vein also consists of thee layers: tunica externa - the outer layer, Tunica
meida - the middle layer, tunica intima - the inner layer, which are less
developed and have less elastic fibers as compared to an artery. The lumen
ofthe vein is large. Semilunar valves are present. Valves are formed from the
folds of the iriner layer of the veins. Valves are present only in the lower part of
the body specially in the abdomen and hind limbs. In the upper region above
the heart there is no valve.

The Heart in Action

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How the heart Contracts? Contraction of human heart is initiated by a wave of depolarization at begins at the SA node. After passing over the right and left atria and causing their contraction, the wave of depolarization reaches the AV node. From there it passes through the AV bundle which has a bundle branch to each ventricle. From the tip of the ventricles, the depolarization is conducted rapidly over their surface by the branching Purkinje fibers.

How the Heart Beats?

Most muscles contract as a result of impulses reaching them from nerves. This is not, however, true of the heart, which will continue beating rhythmically even after its nerve supply has been severed. The heart will go on beating after it has been cut right out of the body. Cardiac muscle is therefore mynogenic i.e. its rhythmical contraction arises from within the muscle itself.

Parts of the heart involved in producing heart beat

Sino-Atrial node (SA Node): There is a specialized, plexus of cardiac
muscles embedded in the upper wall of the right atrium. It is close to where·
the vena cavae enter the atrium. This plexus of cardiac muscles is called sino
atrial (SA) node. SA Node is called the heart's pace maker as it originates
each heart beat. The SA node has been developed from the sinus venousus

and has become a part of the atrium, so it is called Sino atrial node.

Atrio-Ventricular node (AV .Node): There is another specialized group of' cardiac muscle fibers called AV node. It is present near the junction of right atrium and right ventricle.

Bundle of His and Purkinje Fibers: The AV node is connected to a strand of
specialized muscles in the ventricular septum known as the bundle of His or
AV bundle. The bundle branches divide to the right and left, on reaching the
apex of the heart each branch further divides into Purkinje fibers.

Beating Mechanism: The contraction of the heart is initiated by the periodic
and spontaneous electrical excitation of the cells of the SA Node i.e cardiac

impulse. The resulting wave of electrical excitation passes over both the left

and right atria' and causes their muscle cells to contract.

Contraction of Ventricles: The electric impulse cannot be transferred to
the ventricles, directly due to the presence of valves and nonconductive
tissues, The wave eventually reaches the AV node. From the AV node it goes

to the bundle of His and then to the right and left branches of bundles of His.

From these two branches, the electrical impulse passes to the Purkinje
fibers. These Purkinje fibers are extended into walls of the ventricles. So as
the impulse reaches the Purkinje fibers, the ventricles contract.

Reason for the slight delay between the a rial and ventricular
contraction

The wave of electrical impulse does not immediately spread to the
ventricles from the SA node. Almost O.1 second passes before the
ventricles start to contract. The reason for the delay is that the atria of the
heart are separated from the ventricles by connective tissues which cannot
propagate a wave of electrical excitation.

Secondly the cells that carry the wave of impulse from atria to the
ventricle have small diameter. Thus they propagate the depolarization slowly,
causing the delay of contraction of ventricles. This delay permits the atria to
finish the emptying the contents into the corresponding ventricles before the
ventricles start to contract.

ECG: As each wave of contraction spreads through the heart, electrical
current spreads into the tissues surrounding the heart and onto the body
surface. By placing the electrodes on the body surface on the opposite sides
of the heart, the electrical activity can be amplified and recorded by an
electrocardiograph.

The written record produced is called an electrocardiogram or ECG.

Malfunction of the heart causes abnormal currents, which in turn produce an
abnormal ECG.

The Heart

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The heart is a hollow muscular pumping organ. It is somewhat conical in shape. It is about the size of a man’s fist. It lies between the lungs in the thoracic cavity. The heart is enclosed in a thin tough transparent membrane, the epicardium. There is a fluid between the heart and the pericardium. The fluid reduces the friction between the pericardium and the heart. The pericardium is inextensible. The wall of the heart is composed of epicardium, myocardium and endocardium. The thick midlayer (myocardium) consists of cardiac muscle tissue that provides the contractile force behind blood flow through the heart. The smooth inner lining (endocardium) is made brachiocephalic of epithelial and trunk connective tissues. Internally the heart is divided by a vertical partition into two halves, the right and left. The vertical partition is called septum. Each half is again divided by a horizontal partition into an upper thin atrium (Platria) and a lower thick walled ventricle. Thus the heart consists of four chambers, the right and left atria and the right and left ventricles. The atrium of each side communicates with the corresponding ventricle through an opening, the atrio-ventricular opening.

Veins: The two great veins the superior and inferior vena cavae open into the right atrium. The orifice of the superior vena cava is directed obliquely and has no valves. Two, right and left pulmonary veins, open into the left atrium and their orifices are not provided with valves.

Valves: The heart has four sets of membranous flaps that serve as valves. The coordinated opening and closing of the valves permit blood to move in one direction. Atrio-ventricular valves are inlet valves. Tricuspid valve is present in the opening between right atrium and right ventricle. It is made up of three flaps of connective tissues. Bicuspid valve is present in the opening between left atrium and left ventricle. It consists of two flaps. The fore ends of the flaps are attached to the wall of the ventricle by fibrous cord, the cordae tendinae, which prevents the over extension of flaps into the auricles during the ventricular contraction. Semilunar valves are outlet valves. One semilunar valve is located at the passageway leading from the left ventricle to the aorta and another is located between the right ventricle and the pulmonary artery.

human heart dissected

Valves

Circulation of blood in the Heart: atria receive blood and the ventricles distribute it the blood flows into the right atrium through the vena cavae.

Superior Vena Cava: It brings the deoxygenated blood from the upper region of the body.

Inferior Vena Cava: it brings the deoxygenated blood from

the lower region of the body. From right atrium blood flows to the right ventricle, then to the lungs by means of pulmonary arteries for oxygenation. The oxygenated blood returns to left atrium by means of pulmonary veins. Then the blood flows to the left ventricle. From left ventricle the blood is pumped into aorta which carries blood to all parts of the body.

Circulation of Blood in Heart

Cardiac Cycle: The cardiac cycle is a sequence of events during one heartbeat.

Atria Relaxation: Blood enters the right atrium from the body through the

vena cavae. Blood enters left atrium from the lungs through the pulmonary

veins. Both atria fill up and the blood flow into them ceases.

The blood circulation may be summarized as follows:

—>Veins (conduct blood from organs)—*right atrium—> right ventricle—*pulmonary arteries> capillaries in the lungs—>pulmonary veins—>left atrium—*Left ventricle —>aorta—> arteries (conduct blood to organs)—> capillaries.

Atria Contraction: Blood is pushed through the atrio-ventricular valves into
the still relaxed ventricles. The ventricles become full and pressure forces the valves to close preventing a back flow of blood into the atria.

Ventricle Relaxation: Blood is received from the contracting atria.

Ventricle Contraction: Blood pushed against the semi lunar valves at the
base of the aorta and pulmonary arteries. Right and left ventricles have equal volume and both the ventricles pump almost simultaneously, so that equal amount of blood enter and leave the heart.

Ventricle Relaxation: Blood is received from the contracting atria.

One heart beat-a cardiac cycle of relaxation-diastole and contraction systole takes about 0.8 second. The heart muscle rests. 0.1 to 0.3 second between the beats. Each heart beat is accompanied by two heart sounds, lub and dub. The lub dub heart sounds are not caused by the contraction of the heart, but by sudden closing of the valves. The heart beats about 75 times per minute (at rest) pumping out about 5 liters of blood. The heart beat varies with age, sex, size and state of health.

Function of Blood

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Blood performs the following major functions.

The plasma proteins maintain colloid osmotic pressure of the blood out of which 75% by albumins, 25% by globulins and almost none by fibrinogen.
Transport of soluble organic compounds including nutrients, water, salts and waste products.
All hormones are transported by blood from the endocrine tissues to the large cells.
Transport of oxygen and carbon dioxide involves red blood cells.
Defense against diseases. This is achieved in three ways.

a) Clotting of the blood by platelets and fibrinogen which prevents excessive blood loss and entry of pathogens.

b) Phagocytosis performed by the neutrophils, Monocytes and macrophages, which engulf and digest bacteria which find their way into the blood stream and body tissues.

c) Immunity achieved by antibodies and lymphocytes.

Blood produces interferon and antitoxins, which are proteins and protect out body from nucleic acids of invading organisms, and toxins of the invaders.
Maintenance of a constant blood solute potential and pH as a result of plasma protein activity. As the plasma protein and hemoglobin possess both acidic and basic amino acids, these can combine with or release hydrogen ions and so minimize pH change over a wide range pH values. In other words these act as a buffer.
Distribution of excess of heat from the deeply seated organs. This helps to maintain a constant body temperature; blood also maintains concentration of water and salts; thus helps in homeostasis.
Blood helps in exchange of materials between blood and body tissue through blood capillaries.
Blood helps the body in maintaining the internal environment by producing heparin, histamines and also maintaining the amount of chemicals in the body to a constant or nearly constant level.

Blood Cells and Cell like Bodies

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They constitute 45% by volume of the blood. These include red blood cells, white blood cells and platelets.

a) RED BLOOD CELLS: These are called erythrocytes (eurothos, red).

Number: A cubic millimeter contains 5 to 5.5 millions in males and 4 to 4.5 millions in females.

Shape: The erythrocyte is a disk slightly concave on both sides i.e. biconcave. This shape has two advantages (i) it provides a large surface for gas diffusion. (ii) The biconcave shave allows the RBCs to move easily the narrowest blood capillaries without getting trapped.

Structure: RBCs when formed have nucleus, but it is lost before they enter the blood. 95% of the cytoplasm of red blood cells is the hemoglobin. It is an iron containing pigmented compound. It gives red color to the blood.

Formation: In the embryonic stages they are formed in the yolk sac, liver or spleen. After birth they are formed in the bones. In the adult RBCs are formed in marrow of certain short bones such as ribs, sternum (breast bone) spongy bones, vertebrae and end of long bones.

Average Life: An erythrocyte exists for about 120 days in the blood stream before it finally fragments. About 2-10 million red blood cells are formed and destroyed every second in normal person. The fragments of RBCs are engulfed by scavenger cells called macrophages in the liver, bone marrow and spleen. The iron from the hemoglobin is retained and used again. The rest of haeme is converted in liver to bilirubin a bile pigment, which is excreted in the faeces.

Function: RBCs carry oxygen to all cells of the body. RBCs also help in transport of CO₂.

a) WHITE BLOOD CELLS: These cells are called leucocytes (leukos, colorless). These are not white in color. These are colorless. In WBCs hemoglobin is absent i.e. these are not red in color. So these cells are called white blood cells. Their number is 7-8 thousand per cubic ml, and life span is 3-4 days.

Structure: WBCs are classified into two main groups. (i) Agranular (ii) Granular.

(i) Agranular: In these cells the cytoplasm is clear having one nucleus. These cells originate in bone marrow and migrate and also produced in large numbers in the lymph nodes. Examples: (i) Lymphocytes (ii) Monocytes.

(ii) Granular: These are also called polymorph. Nucleus is highly variable in shape. (Poly = many, morph = shape). Nucleus has lobes. Cytoplasm contains fine granules. These originate in bone marrow. Examples: i) eosinophils ii) neutrophils iii) basophils.

Functions: different leucocytes have different functions. Their main function is to protect the body against the invading micro-organisms.

Agranular Leucocytes:

i) Lymphocytes: These are in Lymph Nodes. Lymphocytes produce and carry antibodies and are part of immune system.

ii) Monocytes: These are highly mobile and phagocytic. Monocytes ingest bacteria, other foreign matter and dead cells at the damaged tissue region.

Granular Leucocytes:

i) Eosinophils: Have large granules that stain bright red with eosin, (an acidic dye). Eosinophils are phagocytic and are involved in the control of the allergic reaction. So their number may rise greatly during an allergic reaction.

ii) Neutrophils: These are mobile; many can squeeze between the cells of capillary walls and move like amoeba, forming pseudopodia. Neutrophils are phagocytic cells.

iii) Basophils: Exhibit deep blue granules when stained with basic dyes. These are phagocytic and contain anti clotting chemical heparin that are important in blood clotting. Basophils contain large amount of histamine which these release in injured tissues and in allergic response.

Pus: the leucocytes die when these fight bacteria. The dead leucocytes accumulate at the infected wound. This accumulation of dead leucocytes is called pus.

3) Platelets: Certain large cells within bone marrow called megakaryocytes regularly pinch off bits of their cytoplasm. These cell fragments are called platelets. Thus a platelet is not a whole cell but a fragment of cytoplasm enclosed by a membrane. These contain no nuclei.

Function of Platelets: They play an important role in controlling blood clotting. When a blood vessel is cut, it constricts, reducing loss of blood. Platelets stick to the rough cut edges of the vessel, physically patching the break in the wall. Prothrombin, a plasma protein manufactured in the liver requires vitamin K for its production. In the presence of clotting factors, calcium ions and compounds released from platelets Prothrombin is converted to thrombin. Then thrombin catalyzes the conversion of the soluble plasma protein fibrinogen to an insoluble protein fibrin. Once formed fibrin polymerizes producing long threads that stick to the webbing of the clot. These thread trap blood cells and platelets which help to strengthen the clot.

Plasma

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It is the liquid part of the blood. It constitutes about 55% by volume of blood in a normal person, and the cells form about 45% by volume of the blood. Water constitutes about 90% of plasma and 10% dissolved substances which includes proteins, salts, nutrients and wastes. Most of the dissolved substances are maintained at a constant or nearly constant level, but others occur in varying concentration. The substances dissolved or present in plasma vary in their concentrations, with the condition of the organism and with the portion of the system under examination.

There are six types of solutes.

1) The Plasma Proteins: 7 to 9 % of the plasma is made of different types of proteins. Most of the proteins are synthesized in liver. The plasma proteins perform following functions.

a) Fibrinogen takes part in the clotting process. The protein prothrombin takes part as a catalyst in blood clotting. Plasma without fibrinogen is called serum.

b) Some of the globulins called immunoglobins or antibodies are produced in response to antigens by lymphocyte cells, and then are passed to plasma and lymph. Immunoglobulins play an important role in defenses against disease.

c) Water does not move from the blood vessels into the surrounding cells, as plasma proteins are large to pass readily through the wall of blood vessels, so it maintains osmotic pressure between the blood stream and surrounding medium.

2) Inorganic or Mineral Ions: Plasma is a dilute salt solution. Salts constitute about 0.9 percent of the plasma of humans and more than two thirds of this amount is sodium chloride and bicarbonates. There are trace amounts of calcium, magnesium and metabolic ions including copper, potassium and zinc. Shifts in the concentration of particular ion can create serious disturbances.

3) Organic Nutrients in the Blood: These include glucose, fats, phospholipids, amino acids and lactic acids.

4) Metabolites and Wastes: Amino acids, glucose, vitamins, lipids and metabolic wastes are urea and uric acids.

5) Hormones: All the hormones present in the plasma are to be carried out by the blood.

6) Dissolved Gases: CO_2, O₂, and N₂are present in the plasma.

Blood

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It is the circulatory fluid within the blood vessels. Almost all the substances to be transported by blood are present either dissolved or suspended in the blood. Take some human blood from the vein in a test tube. Add some anticoagulants (heparin, warfarin, fluoride etc.) to prevent from clotting. The blood quickly separates into the upper layer and the lower layer. Upper layer is yellowish, semitransparent and is called plasma. The lower layer contains mainly the blood cells. The weight of the blood is about 1/2th in our body.

Transportation In Man

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The circulatory system can be divided into blood vascular system and the lymphatic system. In blood vascular system the organs concerned are the blood, heart and blood vessels.

Evolution of Vertebrate Heart -- Birds and Mammals

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In birds and mammals the wall between the ventricles is complete, preventing the mixing of oxygenated blood in the left camber with deoxygenated blood in the right camber. The conu has split and becomes the base of the aorta and pulmonary artery. The ventral aorta is divided into two trunks, 1) pulmonary trunk 2) aortic trunk.

Complete separation of the right and left sides of the heart makes it necessary for blood to pass through the heart twice each time it tours the body. As a result, it is possible to maintain higher blood pressure and materials are delivered to the tissues rapidly and efficiently. Because the blood of birds and mammals contain more oxygen per unit volume and circulates more rapidly than in other work to braids, the tissues receive more oxygen. As a result, birds and mammals can maintain a higher metabolic rate and a constant high body temperature even in cold surroundings.

Evolution of Vertebrate Heart – Reptiles

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Reptiles also have a double circuit of blood flow made more efficient by a wall that partly divides the ventricle. The heart consists of two atria and a ventricle. In crocodiles the wall between the ventricles is complete so the heart consists of two atria and two ventricles. In reptiles the ventricle is incompletely divided.

Evolution of Vertebrate Heart – Amphibians

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The amphibian heart has two atria and one ventricle. In addition the sinus venosus and conus arteriousus which divide into two truncus arteriosus are also present. A sinus venosus collects deoxygenated blood from two super vena cava and one inferior vena cava from different parts of the body. Sinus venosus pumps the blood into the right atrium. Blood returning from the lungs passes directly into the left atrium via pulmonary veins. Both atria pump into the single ventricle but deoxygenated blood is pumped out of the ventricle before oxygenated blood enters it. Blood passes into an artery the conus arteriosus with a fold that helps keep the blood separate. Much of the deoxygenated blood is directed to the lungs and skin, where it can be recharged with oxygen. Oxygenated blood is delivered into arteries that conduct it to various tissues of the body.

In amphibians blood flows through a double circuit. The pulmonary circulation delivers it to the lungs and skin, while the systemic circulation transports it to all organs of the body. When the ventricle contracts, it pushes blood via truncus arteriosus to two carotids, two systematic and two pulmocutaneous arches.

Evolution of Vertebrate Heart – Fish

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The heart of fish consists of four chambers, namely 1) sinus venosus, 2) an atrium, 3) a ventricle, 4) conus arteriousus. A thin walled sinus venosus receives blood returning from the tissues and pumps it into the atrium. The atrium contracts and then pumps blood into the ventricle. Ventricle has thick muscular wall. Next, the ventricle pumps blood into an elastic conus arteriosus, which does not contract, and blood flows into aorta.

In fishes blood flows through a single circuit passing through a capillary network in the gills, where blood becomes oxygenated and then through capillaries located in other organs of the body. The oxygenated blood is supplied from dorsal aorta through coronary arteries to the heart and is carried back by coronary veins from the heart. The heart of the fishes never receives oxygenated blood. It is only the deoxygenated blood which passes through different chambers of the heart. The valves present in the heart controls the flow of blood in single direction. So the heart of fish functions as a single circuit heart.

Vertebrate Blood Circulatory System

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The vertebrate circulatory system became modified in the course of evolution as the site of the gas exchange changed from gills to lungs and as vertebrate became active and endothermic animals. The vertebrate heart has one or two atria, chambers that receive blood returning from the tissues, and a single or divided ventricle that pumps blood into the arteries. Additional chambers are present in some classes.

Transportation in Cockroach

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Haemocoel: The body cavity contains blood, so it is called haemocoel. The haemocoel is divided into two cavities by a transverse pericardial membrane. The dorsal cavity is called pericardial cavity (sinus) and the ventral cavity is called perivisceral (Meaning: Surrounding the viscera) cavity. The pericardial membrane is perforated.

Open Circulatory System: Cockroach has an open circulatory system. The blood is not always enclosed in a tube. Much of the time the blood flows in large spaces among the tissues in the body. There are no capillaries.

Haemolymph: The blood of haemolymph is colorless fluid. It contains white blood cells (which act as phagocytes).

Function: Function of blood is chiefly to transport the absorbed nutrients. It has no respiratory figment, so it has nothing to do with respiration. Reparation is performed by tracheal system.

The Blood Vessel: The blood vessel consists of a single, long tubular mid-dorsal blood vessel below the targa. Each segment of thorax and abdomen consists of a dorsal plate the tergum (plural terga) a ventral plate the sternum joined at the sides by soft cuticle the pleuron. The dorsal vessel is differentiated as (i) heart (ii) aorta.

(i) Heart: The part of the dorsal vessel in the abdomen is called heart. It is divided into eight chambers. Each chamber has a pair of lateral openings called ostia. Each ostium has a valve, to prevent backflow of the blood. On the sides of the heart there are alary muscles which help in the flow of blood.

(ii) Aorta: The part of the dorsal vessel that extends in thoracic and head regions is called aorta. It is without chambers. It opens in anterior by a funnel shaped opening into the haemocoel.

Circulation: When the alary muscles contract the heart chambers relax. Blood from the perivisceral cavity passes into the pericardial cavity. It enters the heart chambers through the ostia. When the heart contracts the ostium is closed by valve. The blood is forced along the dorsal aorta. The wave of contraction starts at the posterior end and work their way towards the anterior end. From the heart the blood flows into the aorta. From here the blood reaches the perivisceral cavity in the head region. Then moves backward where it bathes all the organs. It also circulates in the appendages and wings. The blood enters the pericardial cavity through the perforation in the pericardial membrane and again enters the heart through the ostia.

Transportation in Earthworm

2011-06-23T20:41:00.000+05:00

The circulatory system consists of longitudinal and transverse blood vessels, in which blood flows continuously. The circulatory system is complicated and the arrangement of blood vessels behind the 14^th segment is different from the arrangement from the first 14^th segments. So a general plan of circulatory system in earthworm is being discussed.

There are three main longitudinal blood vessels, besides smaller vessels, 4/5 pairs of hearts found in earthworm:

1. Dorsal Vessel: It runs throughout the length of the body in the mid dorsal line. It is present above the alimentary canal. Its wall is thick and muscular. It shows rhythmical peristaltic contraction from behind to the front. The backward flow is prevented by a pair of valve present in front of each septum (septum is partition wall between the segments). It serves only as a collecting vessel. It receives blood from intestine, nephridia, body wall etc. in the first 14^th segment, the dorsal vessel becomes a distributing vessel. It supplies blood to anterior region, of the earthworm. It also sends blood to the four pairs of hearts. The hearts pump the blood into the ventral vessel.

2. Ventral Vessel: It runs throughout the length of the body below the alimentary canal. It is a distributing vessel only. The blood flows from anterior to posterior end. Valves are absent in its lumen (space). A number of small blood vessels are given off, which distribute blood to the body wall, septa and nephridia of each segment.

3. Sub-Neural Vessel: It extends along the mid-ventral line of the body wall below the nerve cord and extends from 14^th segment backwards. In each segment, it collects blood from the nerve cord and from ventral region of the body wall and the flow of blood is backward. Sub neural vessel in the 14^th segment divides into two lateral oesophageal vessels. Sub-neural vessel communicates with the dorsal blood vessel through commissural vessel.

4. Supra Oesophageal Vessel: It runs from 9^th to 13^th segment, between dorsal vessel and the oesophagus. At posterior it is connected with the ventral vessel through the two latero-oesophagal hearts.

5. Hearts: The number of hearts depends on type of the species. It maybe 4 or 5 pairs. Hearts are situated in the 7^th to 13^th segments. They are also called aortic arch. The heart pumps blood from the dorsal to the ventral vessel. The flow of blood cannot be reversed due to the arrangement of the valves at the junction of dorsal vessel and hearts.

6. Valves: The direction of flow of blood is controlled by valves. They are present in the (i) Dorsal vessel (ii) Heart (iii) at the points of junction of the chief vessels with the dorsal vessels.

7. Blood: It is bright red in color due to the presence of hemoglobin, which is dissolved in plasma. There are also corpuscles in the blood which are colorless and nucleated.

Transportation in Earthworm

8. Distribution of Food: The branches of the ventral vessels that enter the wall of the digestive tract also break up into innumerable capillaries. The product of digestion such as amino acids and glucose enters the capillaries. The capillaries of the intestinal wall join to the dorsal vessel. Thus the end products of digestion are distributed to all parts of the body.

Types of the Circulatory System

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Two distinct types of blood vascular systems are found in animals. These are opened and close blood circulatory system.

Open Circulatory System: Blood is pumped by the heart into an aorta which branches into a number of arteries. These open into a series of blood spaces collectively called haemocoel. In other words, blood does not stay in the vessels, hence the term ‘open’ is used. Blood under low pressure moves slowly between the tissues, gradually percolating back into the heart through open-ended veins. Distribution of blood to the tissues is poorly controlled.

It is observed in animals belonging to phylum Arthropoda e.g. Crustaceans, spider insects, and phylum Mollusca e.g. snails and calms ad group of protochordates the tunicates.

Closed Circulatory System: Blood is confined to a single set of branching vessels, through which it is moved under pressure by one or more hearts. The blood travels in a circuit following the same pathway again and again as it is pumped through the body. The blood flows from arteries to veins through the capillaries. So the system in which the blood travels in blood vessels and the whole blood do not come in contact with cells is called closed circulatory system.

It is observed in animals belonging to Annelids e.g. earthworms, cephalopods e.g. squids, octopus, echinoderms and vertebrates. From the evolutionary point of view it is regarded as the most advanced type. It has (a) great efficiency (b) maintenance of blood pressure (c) economy of blood volume.

General Characteristics of a Blood Vascular System

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The purpose of a blood vascular system is to provide a rapid mass flow of materials from one part of the body to another. A circulatory system has three distinct characteristics.

a) A circulatory fluid, the blood.

b) A contractile, pumping device to propel fluid around the body. This may either be a modified blood vessel or a heart.

c) Tubes through which the fluid can circulate, the blood vessels.

Circulatory System

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As organisms increase in size and complexity, the quantity of materials moving in and out of the body increases. The distance that materials have to travel within the body also increases, so that diffusion becomes inadequate as a means of their distribution. Some other methods of conveying materials from one part of the organism to another is, therefore, necessary. This generally takes the form of a mass flow system. There are two circulatory systems which rely on mass flow in animals, namely the blood vascular system and the lymphatic system.

Transportation in Planaria

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Planarians are generally 10mm in length. They have no special transport system. The movement of materials into and out of the cells takes place by diffusion. There are several reasons for this:

A) Body is greatly flattened, so that every call is close to the outside.

B) Are cells are loosely arranged, so diffusion can take place easily.

C) The distribution of digested food materials is performed by the digestive sac itself, which occupies much of the interior. No parts of the body is far from some branch of the digestive sac.

D) For the transport of liquid wastes and their removal to the outside the planarians have an excretory system.

Transportation in Hydra

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It is 2-3 mm in length and is about half mm in diameter, so it is large enough to be seen. It has no specialized transport system. Nearly every cell of hydra is adjacent either to the outside pond water or to the water in the digestive cavity. Movement and absorption of digested food is by diffusion.

Transport In Animals

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In one celled organisms, exchange of materials occur by passive and active transport directly with the environment. These processes are used in sponges, coelenterates and flatworms. These organisms are composed of only a few cell layers. No cell is very far from its environment. Therefore materials can be exchanged quickly.

Larger and more complex organisms have specialized system to exchange materials between cells and their environment, in the form of blood vascular system.

Critical Amendments Of Pressure Flow Hypothesis

2011-06-12T07:33:00.002+05:00

The hypothesis that mass flow will occur through sieve tubes and this seems to occur.
The hypothesis requires the existence of an osmotic gradient and high pressure gradient in a number of plants.
Little metabolic energy is expended by living sieve tubes, suggesting that movement of solutes through them is passive as predicted by the pressure flow hypothesis.
Sieve plates are thought to be necessary, despite the resistance to flow which they create, to support sieve tubes, preventing them from bulging and splitting, with the high internal pressure.

Pressure Flow Mechanism

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The most widely accepted hypothesis, explaining phloem transport is called pressure flow mechanism, first proposed by Munch in 1927. two regions can be recognized in the plants, source and sink.

Sugar is actively loaded into the sieve tube element at the source. As a result of differences in water potential, water moves osmotically into the sieve tube element. At the sink sugar is actively unloaded and water leaves the sieve tube element by osmosis. The gradient of sugar from source to sink causes pressure flow through the sieve tube toward the sink.

An area where sugar is made is called source e.g. green leaves and stem. Any area where sugar is stored or used is called sink e.g. young leaves, fruits, seeds and roots. According to pressure flow mechanism water containing sugar in solution flows under pressure through the phloem. It involves the following.

a) Glucose is produced by photosynthesis in the mesophyll cells of the green leaves. Some glucose is used within the cells during respiration. The rest of glucose is converted into non-reducing sugar i.e. sucrose.

b) It has been shown that the sucrose concentration in sieve tubes in leaves is commonly between 10 to 30 percent whereas it forms only 0.5% solution in the photosynthesis cells.

c) The sucrose is actively transported to the companion cells of the smallest vein in a leaf.

d) The sucrose diffuses through the plasmodesmata to sieve tube elements. As a result, concentration of sucrose increases in the sieve tube cells or elements. The sucrose is actively transported to the sieve elements.

e) Water moves by osmosis from the nearby xylem in the leaf vein. This increases the hydrostatic pressure of the sieve tube elements.

f) Hydrostatic pressure moves the sucrose and other substances in the sieve tube cells, and then moves to sink. In the storage sinks, such as sugar beef root and sugar cane stem, sucrose is removed into apoplast prior to entering symplast of the sink.

g) Water moves out of sieve tube cells by osmosis, lowering hydrostatic pressure. Thus the pressure gradient is established as a consequence of entry of sugars in sieve elements at the source and removal of sugar i.e. sucrose at the sink.

h) The presence of sieve plates greatly increases the resistance along the pathway and results in the generation and maintenance of substantial pressure gradient in the sieve elements between source and sink.

The sieve elements contents are physically pushed along the transportation pathway by bulk flow. The pressure flow theory accounts for the mass flow of molecules within phloem. As the sap is pushed down the phloem sugar is removed by the cortex of both stem and root and is consumed or converted into starch. Starch is insoluble and exerts no osmotic effect. Consequently the osmotic pressure of the contents of phloem decreases. Finally relatively pure water is left in the phloem and this is thought to leave by osmosis or be drawn back into nearby xylem vessels by suction of the transpiration pull.

The pressure flow mechanism depends upon: 1) Turgor pressure 2) Difference of osmotic pressure gradient along the direction of flow between the source and the sink.

The objection leveled against the pressure flow mechanism is that it does not explain the phenomenon of bidirectional movement i.e. movement of different substances in opponent directions at the same time. The phenomenon of bidirectional movement can be demonstrated by applying two different substances at the same time to two different points of phloem of a stem and following their longitudinal movement along the stem. The bidirectional movement occurs in a single sieve tube or not. If the mechanism of translocation operates according to pressure flow hypothesis, bidirectional movement in a single sieve tube is not possible. Experiments to demonstrate bidirectional movement in a single sieve tube are technically very difficult to perform. Some experiments indicate that bidirectional movement may occur in a single sieve tube, whereas others do not.

Phloem Parenchyma, Fibers and Sclereids

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Phloem parenchyma and fibers are found in dicotyledons but not in monocotyledon’s phloem. Parenchyma are thin walled, and elongated. Phloem fibers occur in bundles and in phloem provide mechanical support. Sclereids occur frequently in phloem.

Companion Cell

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Closely associated with each tube element are one or more companion cells. It is living and complete cell, and metabolically very active. Companion cells are essential for the survival of sieve tube elements.

Sieve Tube

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These are formed by the end to end fusion of cells. Their walls are made up of cellulose and pectin substances, and their nuclei degenerate, but the sieve elements remain living and are dependent on the adjacent companion cells. A characteristic feature of sieve tube is the sieve plate. Originally plasmodesmata runs through the walls but the canals enlarge to form pores, making the walls look like a sieve and allowing a flow of solution from one element to the next.

Features Of Phloem In Relation To Their Transport

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Phloem is tubular structures modified for translocation. The tubes are composed of living cells with cytoplasm. There are five cell types in the phloem namely sieve tube elements, companion cells, parenchyma, fibers and sclereids.

Translocation of Organic Solutes

2011-06-09T12:47:00.000+05:00

Not only do plants transport water and minerals from the roots to the leaves, they also transport organic nutrients to the parts of plants that need them. This includes young leaves, flowers, seeds, fruits and especially the roots. Phloem tissues transport organic nutrients. This is shown by feeding habits of aphids.

Feeding Habit of Aphids: The feeding habit of small insects that suck the juice of plants, gives us valuable information about translocation. An aphid feeds on leaves and stem. It inserts the mouth parts or stylets or proboscis into a sieve tube, which contains sugary fluid.

Honey Dew: The sieve tubes are under high turger pressure. The sieve tube sap is forced through the gut of the aphid. The sap comes out of the posterior and of the gut as droplets called honey dew.

Transpiration as a Necessary Evil

2011-06-07T16:59:00.000+05:00

The stomata are primarily meant for absorption of CO2 but these also help in exchange of gases, but at the same time water vapors also escape through stomata. Thus transpiration is described as necessary evil because it is an inevitable process but potentially harmful. Loss of water can lead to wilting, serious desiccation, and often death of a plant, if there is shortage of water. There is good evidence that even mild water stress results in reduced growth rate, and reduction in yield.

However, transpiration is beneficial to the plants in several ways.

1) Mineral Absorption: Minerals absorbed in water are absorbed into the roots; move up through the plant in the transpiration stream.

2) Optimum Turgidity: In some plants if transpiration is not allowed to occur, plants become very turgid, do not grow well and there is shortage of water in their cells.

3) Energy Exchange: When water is evaporated from the exposed surface of cells of leaves, it exerts a cooling effect on plant.

4) Effect on Growth and Development: Transpiration is a necessary factor in the normal growth of some plants e.g. pear, sunflower.

5) Absorption of Water: Water is conducted or transported in upward direction in most tall plants due to transpiration.

6) Exchange of Gases: Wet surface of leaf cells allow gaseous exchange.

Factors Affecting Transpiration

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Factors that affect transpiration are:

a) Temperature

b) Light

c) External Humidity

d) Air Circulation

e) Soil moisture

f) Carbon-dioxide Concentration

Let's discuss all the above factors in detail.

a) Temperature: When there is an increase in temperature, the capacity of the air to hold the water decreases, thus water vapors from the leaves can diffuse easily. The rate of water evaporation doubles for every temperature rise of about 10 degree Celsius. This increase in transpiration with increasing temperature is up to certain point. If temperature exceeds from 30 to 45 degrees Celsius the stomata are closed.

b) Light: Light affects transpiration by opening the stomata. In the dark the stomata become closed and rate of transpiration decreases. Light absorbed by the mesophyll cells increases the internal temperature of the leaf. This increase in temperature causes increase in the rate of transpiration. K+ actively enters the guard cells when light is available and water follows and guard cells become turgid and stomata opens.

c) External Humidity: The difference in the water content of the plant and that of the atmosphere affects the rate of transpiration. When the atmospheric air is fully saturated with water vapors, there is no possibility of more water vapors moving into it. Transpiration takes place when the atmosphere is partially unsaturated or dry. In green house the floor and wall are watered to increase humidity and to reduce transpiration from the plants. This reduces the possibility of wilting and results in better growth.

d) Air Circulation: When the air is still, the air surrounding a leaf becomes saturated thus transpiration is reduced. When the air surrounding the leaves is in motion, it is carried away before it can become saturated, so water vapors can diffuse outwards continuously.

e) Soil Moisture: When the amount of soil water is low, less water is absorbed by the plant. The amount of water in the guard cells falls, they become flaccid and close up the stomatal pores and transpiration decreases. The opposite takes place when an excess of soil water is available to the plant.

f) CO2 Concentration: Low CO2 Concentration stimulates the active transport of potassium ions into guard cells. This transport causes stomata to open and allow CO2 to diffuse in the mesophyll cells of leaves. At night cellular transpiration in the absence of photosynthesis raises CO2 levels. This stops the inward transport of K+ ions and thus of water, allowing the guard cells to close.

Opening and Closing of Stomata

2011-06-03T15:45:00.000+05:00

There are two hypothesis which may explain the opening and closing of stomata.

1) Starch Sugar Hypothesis

2) Influx of K+ ions

Starch Sugar Hypothesis

It was proposed by German Botanist H. Van Mohl. The guard cell absorbs Carbon dioxide. Some CO2 reacts with water in which it is dissolved to form carbonic acid. In the presence of light energy, carbonic acid in the guard cell is converted into CO2 and water, which are rapidly used in the synthesis of Carbohydrates. The contents of illuminated guard cell is: I) The acid concentration is low i.e. pH is high. II) Sugar concentration is high. As sugar concentration increases in the guard cells, as a result water enters the guard cells. The guard cells become turgid (swollen with water). The thin outer walls bulge out and force the inner wall into a crescent shape. In this way a stoma or pore is formed between each pair of guard cell.

Closing of Stomata

In the dark, most of the sugar molecules are removed by respiration or are converted into insoluble starch. So there is an increase in the acidity of the cell contents. As sugar molecules are removed from the guard cell and the relative concentration of water in the guard cell increases, water molecules diffuse out to the epidermal cells. As the guard cell loses water, it becomes flaccid. In contrast to turgidity the loss of water causes them to become weak limp and soft. This condition is known as flaccidity and the cells are said to be flaccid. The inner thick wall moves together until the pore between them is closed. Closing of stomata prevents I) loss of water vapor II) the entry of carbon-dioxide into the leaf. The CO2 produced during respiration is used for photosynthesis even though the stomata are closed.

Influx of K+ ions

The K+ ions concentration in guard cells increase many times depending upon plants species. K+ ions (shown in red dots in the figure) enter guard cells from the surrounding epidermal cells by active transport. The accumulation of K+ decreases the osmotic potential of guard cells. Water enters the guard cell by osmosis. The guard cells become turgid and are stretched and stomata are opened. The guard cells remain in this condition only so long as the pumping of K+ ions into the cell is continue. So for keeping the stomata open a constant expenditure of energy is required.

In darkness K+ ions move out of the guard cells into surrounding epidermal cells. The water potential of guard increase as a result. Water moves out of the cells. The loss of pressure makes the guard cells change their shape again and stomata closes. Level of CO2 decreases in the spaces inside the leaf and light controls the movement of K+ into and out of guard cells. A low level of CO2 favors opening of the stomata and thus allow an increased CO2 level and increase rate of photosynthesis.

Blue light acidify the environment of the guard cells i.e. Pumps out protons which enable the guard cells to take up K+ following by water uptakes as a result turgidity of guard cell increases. In general stoma are open during day and close at night. This prevents needless loss of water by plants when it is too dark for photosynthesis.

Structure of Stomata

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The stoma (singular) is surrounded by two guard cells. The guard cell contains a nucleus and chloroplasts. The guard cells are the only cells of leaf epidermis which have chloroplast. The inner wall of each guard cell is thick and elastic. The outer wall is much thinner. The guard cell is surrounded by epidermal cells. The stoma leads into air spaces that surround thin walled mesophyll cells. Water evaporates from the surfaces of mesophyll cells and the air, in the sacs, becomes saturated with water vapors.

Stomata

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These are present on the young stem and on the leaves. These are usually confined to the lower epidermis of dorsoventral leaves. The isobilateral leaves e.g. Lily and Maize, stomata are present on both upper and lower epidermis.

Stomatal Transpiration

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Largest amount of transpiration takes place through stomata. Water diffuses from the mesophyll into the air chambers and from the chambers, water vapors diffuse through stomata into the atmosphere. Stomatal transpiration involves two processes.

a) Evaporation of water from the cell wall surfaces of sponge mesophyll, bordering the air spaces.
b) Diffusion of water from the inter-cellular spaces into the atmosphere through stomata.

Lenticular Transpiration

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Lenticels are the aerating pores formed in the bark of the stem through which exchange of gases take place e.g. Rose, Hibiscus. Externally lenticels appear as scars on the surface of stem. It consists of a lose of small and thin walled cells. A small fraction of water loss also occurs through the lenticels.

Cuticular Transpiration

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The leaf is covered by a layer of cuticle, which is made up of cutin (a wax like substance). 5 to 7% of water is lost through the cuticle of the leaf surface. The loss of water in form of vapors through the cuticle of leaves is called Cuticular transpiration. Thinner the cuticle the greater is the rate of transpiration. At night when the stomata are almost closed Cuticular transpiration takes place.

Types and Mechanism of Transpiration

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Water forms a film around the mesophyll (palisade and spongy layer of leaf) cells and evaporates into the substomatal chamber from where it diffuses out into air. There are three types of transpiration. (1) Cuticular Transpiration (2) Lenticular Transpiration (3) Stomatal Transpiration.

Transpiration

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The loss of water in the form of vapors from a plant surface is called transpiration. Water escapes through: (a) open stomata (b) epidermal cells. The rate of transpiration is greater when the leaf cells are fully turgid and also when the relative humidity in the atmosphere is low. It also depends on the degree of the opening of the stomata and the surface area of the leaf.

Incipient Plasmolysis

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The point at which the plasmolysis is just about to happen, i.e. the plasma membrane start pulling away from the cell, is called incipient plasmolysis. At incipient plasmolysis the protoplast has just ceased to exert any pressure against the cell wall, so the cell is flaccid.

Distilled water have higher water potential than the contents of the cell. If a plasmolysed cell is placed in distilled water, the water enters the cell by endosmosis, volume of the protoplast increases and it begins to exert pressure against the cell wall of plant cell. The pressure exerted by the protoplast against the cell wall is called pressure potential. As the pressure potential of the cell increases due to endosmosis the cell becomes turgid. Full turgidity is achieved when the cell is placed in distilled water.

The turgid animal cells burst in a solution of higher water potential, due to lack of cell wall. The animal cells use the mechanism of osmoregulation to maintain the amount of water and salts in their cells to a constant or nearly constant level.

Deplasmolysis

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When the plasmolysed cell is kept in water, the cell will return to the original position. This is called deplasmolysis and the cell is said to be deplasmolysed.

Plasmolysis

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When a living cell lies in a medium having higher osmotic concentration i.e. concentration of salt or sugar than that of the contents of the cell, water comes out of the cell by exosmosis. The cytoplasm shrinks and the plasmalemma gets detached from the cell wall. This shrinkage of protoplasm is called plasmolysis and the cell is called plasmolysed.

Pressure Potential Ψ s

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If pressure if applied to pure water or a solution, its water potential increases. This is because the pressure is tending to force the water from one place to another. Such a situation may occur in living cells. For example, when water enters plant cells by osmosis, pressure may build up inside the cell making the cell turgid and increasing the pressure potential. (Also, water potential of blood plasma is raised to a positive value by the high blood pressure in the glomerulus of the kidney). Pressure potential is usually positive, but in certain circumstances, as in xylem when water is under tension (negative pressure) it maybe negative.

Solute Potential Ψ s

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The effect of dissolving solute molecules in pure water is to reduce the concentration of water molecules and hence to lower the water potential. All solutes therefore have lower water potentials than pure water. The amount of this lowering is known as the solute potential. In other words, solute potential is a measure of the change in water potential of a system due to the presence of solute molecules. Ψ s is always negative. The more solute molecules present, the lower (more negative) is Ψ s.

Advantages Of Using Water Potential

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Using the term water potential, the tendency for water to move between any two systems can therefore be measured, not just from cell to cell in a plant, but also, for example, from soil to root or from leaf to air. Water can be said to move through a plant down a gradient of water potential from soil to air. The steeper the gradient, the faster the flow of water along it.

Water Potential (symbol Ψ, The Greek Letter Psi)

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Water potential is a fundamental term derived from thermodynamics. Water molecules possess kinetic energy, which means that in liquid or gaseous form they move about rapidly and randomly from one location to another. The greater the concentration of water molecules in a system, the greater the total kinetic energy of water molecules in that system and the higher is its so-called water potential. Pure water therefore has the highest water potential. If two systems containing water are in contact (such as soil and atmosphere, or cell and solution) the random movements of water molecules will result in the net movement of water molecules from the system with the higher water potential (higher energy) to the system with the lower water potential (lower energy) until the concentration of water molecules in both systems is equal. This is diffusion involving water molecules.

Note the following main points:

1) Pure water has the maximum water potential, which by definition is zero.

2) Water always moves from a region of higher water potential to a region of low water potential.

3) All solutions have lower water potentials than pure water and therefore have negative values of Ψ (at atmospheric pressure and a defined temperature).

4) Osmosis can be defined as the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

Osmosis

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Osmosis can be regarded as special kind of diffusion in which water molecules are the only molecules diffusing. This is due to the presence of partially permeable membrane which does not allow the passage of solute particles. Osmosis is the movement of water molecules from a region of their high concentration (a dilute solution) to a region of their low concentration (a more concentrated solution) through a partially permeable membrane.

In 1988 the institute of biology recommended the use of the term water potential to describe water movement through membranes. The two main factors affecting the water potential of plant cells are solute concentration and the pressure generated when water enters and inflates plant cells. These are expressed in the terms of solute potential and pressure potential respectively.

The Vacuolar Pathway

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In the vacuolar pathway water moves from vacuole to vacuole through neighboring cells, crossing the symplast and the apoplast in the process and moving membranes and tonoplast by osmosis. It moves down a water potential gradient.

The Symplast Pathway

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Movement of cell sap that involves cytoplasmic connection of adjacent cells is termed as symplastic transport or pathway. The symplast is the system of interconnected protoplast in the plant. The cytoplasm of the neighboring protoplast is linked by the plasmodesmata, the cytoplasmic stands which extend through pores in adjacent cell walls. Once water and any solutes it contains are taken into the cytoplasm of one cell it can move through the symplast without having to cross further membranes. Movement might be aided by cytoplasmic streaming. The symplast is an important pathway of water movement.

The Apoplast Pathway

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The apoplast is the system of adjacent cell walls which is continuous throughout the plant. When water moving through spaces in the cell walls reaches the endodermis, its progress is stopped by the casparian strips, a band of suberin and lignin bordering four sides of root endodermal cells. Therefore water and solutes particularly salts in the form of ions must pass through the cell surface and into the cytoplasm of the cells of the endodermis. In this way the cells of the endodermis can control and regulate the movement of solutes through the xylem.

Uptake Of Water By Roots

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The cell wall of epidermal cells of roots is freely permeable to water and other minerals. The cell membrane is differentially permeable. From root hairs water enters the epidermal cells by osmosis. The water moves along the concentration gradient. It passes through cortex, endodermis, and pericycle and reaches the xylem vessels. There are three pathways taken by water to reach the xylem tissues. (1) The apoplast way, (2) the symplast way, (3) the vacuolar pathway.

Facilitated Diffusion

2011-04-27T18:53:00.000+05:00

Facilitated transport or diffusion is the passage of molecules across the plasma membrane. There is reversible combination of molecules with carrier proteins which transport them through the plasma membrane.

Active Transport

2011-04-26T21:04:00.000+05:00

When the concentration of minerals is higher inside the roots than in the soil solution plants can take the minerals from the soil by the process called active transport. During active transport ions move from their low concentration to their higher concentration i.e. against the concentration gradient, through the cell membrane by using ATP energy.

Transport In Plants

2011-04-25T15:54:00.000+05:00

UPTAKE AND TRANSPORT OF MINERALS AND WATER

The roots of a plant absorb minerals from the soil. The root systems have millions of tiny root hairs. Root hairs are projections of outer epidermal cells. Most of the minerals enter the root hairs or epidermal cells of roots along with water in bulk flow, but some are taken in by diffusion, facilitated diffusion or active transport.

MINERAL ABSORPTION BY ROOTS

A root hair is long and narrow. This increases the surface area. Volume ratio which in turn enhances the rate of absorption of water and mineral salts. The cell sap contains sugar, amino acids and salts. It is more concentrated than the soil solution and it is prevented from leaking out by the cell surface membrane. This results in water entering the root hair by osmosis.

The minerals are dissolved in the soil water. The concentrations of the minerals vary according to the fertility and the acidity of the soil. The plants cannot absorb the minerals which are not dissolved and bounded by ionic bonds to the soil particle.

The uptake of minerals by root cells is a combination of passive uptake and active uptake. It involves energy in the form of ATP. The minerals also move down their gradient through plasmodesmata up to xylem cells. From here the minerals are distributed to different parts of the plants by the process of transpiration pull.

The diffusion of ions along with water also takes place by mass flow along the apoplast pathway. Ions moving in the apoplast can only reach the endodermis where casparian strips prevent further progress. The transverse and radial cell walls of endodermal cells are covered with characteristics wall thickenings called casparian strips. These are impregnated with suberin, a substance impermeable to water. That is the water with its dissolved substances cannot pass around the endodermal cells via their walls.

To cross the endodermis ions must pass by diffusion or active transport into endodermis cells, entering their cytoplasm, and possibly their vacuoles. The ions then reach the xylem cells. Diffusion of ions can also take the vascular pathway where ions move along their concentration gradient through the cell membranes, cytoplasm and tonoplast (the membrane of vacuoles) and reach the dead xylem cells.

Need For Transportation

2011-04-25T15:18:00.001+05:00

All living organisms must obtain and transport certain materials within the body. They must also transport and remove the wastes out of their bodies. In one celled organisms exchange of materials occurs through diffusion. In the few cell layered organisms cells are not far from environment, therefore materials can be exchanged quickly.

Diffusion is a slow process, therefore large and complex organisms cannot depend only on diffusion. So all the higher organisms must have a system to transport molecules. The transport system is a link between the cells of the organism and its environment. The transport system brings necessary materials to the cells from specialized areas and takes wastes to other specializes areas. This provides a rapid movement of materials into and out of the organisms.

Transportation

2011-04-25T15:11:00.000+05:00

Every cell depends on its environment. The environment is the source of necessary materials. The process by which the materials get into and out of the cells are diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis. In plants the processes of respiration, transportation, photosynthesis, absorption by roots and conduction of water and the nutrients are involved in movement of materials into, within and out of the body. In animals, respiratory, circulatory, digestive and excretory systems take part in the movement of materials within and out of the body.

Virtual Grassland Picture

2011-04-22T20:44:00.000+05:00

Air And Water As Respiratory Medium

2011-03-01T16:49:00.000+05:00

Gaseous exchange refers to the exchange of respiratory gases between the cell of the organisms and their environment. Respiration is the process by which chemical energy in organic molecules is released by oxidation. This energy is made available to living cells in the form of ATP. The biochemical process which occurs within the cell is called cellular respiration or internal respiration. If it requires oxygen, it is described as aerobic respiration, if the process takes place in the absence of oxygen; it is described as anaerobic respiration. During internal respiration, oxygen enters the cells from liquid medium (blood, lymph, or water, and carbon dioxide diffuses into the same liquid. In complex animals, there are specialized regions for the exchange of gases between the circulating fluid and the external environment. Gas exchange at these points is known as external respiration.

Need of Respiratory Gas Exchange

2011-03-01T16:36:00.000+05:00

The Kingdom Animalia

2010-07-21T21:35:00.000+05:00

The name Animalia is derived from Latin word anima meaning breath or soul. All the animals of the world are included in the kingdom Animalia. Animals are incredibly diverse in structure. They range from worms, only seen with a microscope, to blue whales which weigh up to 150 tons. But typically all animals including humans are multicellular heterotrophs that ingest food. Most have tissues and locomote by means of muscles fibers. The adult is always deployed and it during sexual reproduction that embryo undergoes specified developmental stages.

Animals are believed to have evolved from aquatic protoctist ancestors some 600 million years ago or earlier.

EVENTS OF THE MITOSIS

2010-06-15T19:50:00.001+05:00

The process of cell division was studied in animals by Walther Flemming and in plants by Strassburger. Mitosis takes place in somatic cells. Plant meristems, particularly young root tips are useful for this study. The description given here is based upon the animal cells. The division of mitosis can be divided into two main phases – karyokinesis, during which the nucleus divides, and cytokinesis when a complete division of the cytoplasm is affected. During karyokinesis the various nuclear events had been divided into four phases i.e. prophase, metaphase, anaphase and telophase. These divisions have been made for convenience of study otherwise most of these events occur continuously which are below.

Cell Division - MITOSIS

2010-06-15T19:47:00.000+05:00

There are two main types of cell division, mitosis and meiosis.

Mitosis is type of cell division during which the haploid number (2n) of chromosomes is kept constant in daughter cells. Mitosis involves a series of complex changes in both the nucleus and the cytoplasm. Before the cell divides by mitosis, its basic components are already duplicated, specially the DNA, during interphase.

Interphase is the period during which a cell is not actively dividing, when other activities such as DNA synthesis take place. Interphase is very active phase of cell cycle during which the DNA and histones are duplicated and various proteins which are necessary for cell division are synthesized.

Chromosomes - Their Organization

2010-06-10T13:10:00.000+05:00

Chromosomes are important components of the cell and were discovered by Waldeyer (1876). Soon after their discovery, many biologists, many biologists became interested in their role and it was established by W.S. Sutton (1908) that units of inheritance (genes) are located on the chromosomes and genetic phenomenon can be explained in terms of chromosomal behavior during cell division.

At the onset cell division, the chromatin material of the nucleus condenses into chromosomes. The morphology of the chromosome is best studied during metaphase and anaphase of cell division. A typical chromosome during these stages, comprises of two chromatids (un-separated replica of the chromosome) attached to the same centromere, where spindle fibers get attached during cell division. The position of centromere on the chromosome is very important as it determines the shape of the chromosome and is a basis for the identification of chromosomes from one another. Chromosomes are divided into four types based on their centromeric position. Telocentric chromosomes have the centromere located at one end of chromosome. Acrocentric chromosomes have a very small or short arm. Submetacentric chromosomes have arms of unequal length and Metacentric chromosomes have equal or almost equal arms. Apart from this classification, chromosomes vary from each other due to their size, thickness and other characters as well. Karyotype is a term given to the total chromosome complement of a cell. This involves the number of chromosomes, their relative size and position of centromere etc. So the study of Karyotype helps us in the identification of chromosomes in the human and other species.

Chemical composition of chromosomes has revealed that it is composed of DNA and basic proteins called histones. DNA and histones together form a structure called nucleosome. Under the electron microscope, nucleosome can be visualized as beads about 10 nm in diameter. The chromatin is formed by a series of repeating nucleosome units, which are closely attached to each other to form a continues fiber. Each nucleosome is formed by eight molecules of various types of histones (octamere) and is repeated after every 200 nucleotides of the DNA giving the appearance of chromatin material like beads on a string. Two turns of DNA are stabilized or “sealed off” on the nucleosome by one molecule of another type of histones protein.

Reproduction of Cells

2010-06-10T12:43:00.001+05:00

Reproduction involves the multiplication of cells. The formation of a bud in a simple animal like Hydra the development of sex cells, and the growth of a young animal or plant into an adult all involve cell multiplication.

In order to multiply, cell undergo cell division: one divides into two, two into four, four into eight, and so on. The word division is misleading in some ways because it implies that the process always involves halving the cell and its contents. In fact we now know that cell division is accompanied or preceded by the formation of new cell components so that the products of cell division, the daughter cells, are essentially similar to the parent cell. Understanding cell division is largely a question of appreciating how this uniformity is preserved.

Harmful Effects of Fungi

2009-12-29T20:09:00.001+05:00

Fungi cause number of diseases. They can seriously damage crops. Rust and smut diseases of wheat, rice, corn and other cereals have caused serious damage to these crops. This has resulted displacement of hundreds of millions of humans and has caused countless deaths due to starvation. Potato blite, powdery mildew, ergot of rye, red rot of sugarcane are some other common diseases of plants are caused by fungi. In men they cause skin diseases like ringworm, and athlete's foot. They also infect lungs and genital organs. Fungi cause tremendous amount of spoilage of food stuff, timber and leather goods. Wood rotting fungi infect and destroy not only living trees but all kinds of structural timber.

Beneficial effects of Fungi

2009-12-29T20:07:00.002+05:00

Fungi like bacteria are decomposers and play an important role in nature’s cycle. Beneficial fungi are of great importance, commercially. Some fungi are used in food protection. Yeasts are used in liquor and bread production. Yeasts have also proved extremely in all quests of knowledge of outer space. Pink bread mold neurospora has been extensively used to help us to understand the principles of inheritance. The medically important antibiotic penicillin is obtained from the genus penicillium. Penicillium is also used in cheese production. Certain fungi are edible. These include delicious morels and truffles. Mushrooms are of agricultural importance. About 200 species of mushrooms are edible. Some mushrooms like amanita are poisonous. Only an expert can distinguish the edible mushroom from the poisonous mushrooms. Michorizhae are fungal associations with roots of higher plants. Fungi provide certain essential elements to the plant and the plant provides food to the fungus. Such symbiotic relationships are there in 90 percent of all families of higher plants.

Adaptation of Fungi for Terrestrial Mode of Life

2009-12-29T20:07:00.001+05:00

In fungi, important adaptations for terrestrial mode of life are the disappearance of flagellated cells and evolution of new methods of sexual and asexual reproduction (as in rhizopus), Evolution of protective layers around spores and in some cases around zygote and the evolution of hyphae with thickened supporting walls. Sporangiophores are the structure on which spores are produced and elevated for dispersal. Hyphae are also modified for sexual reproduction.

Sexual Reproduction in Rhizopus

2009-12-29T20:06:00.001+05:00

Sexual reproduction is by conjugation. Hyphae belonging to different strains (plus and minus strains) come in close contact with one another. Tips of the hyphae are separated by septa from the rest of the hyphae. Each tip contains many nuclei with cytoplasm, mitochondria and food material. The two tips are called gametangia. The walls of the gametangia that are in contact dissolve away allowing the two protoplasts to fuse. The zygote resulting from this fusion develops into a zygospore. Zygospore has a thick wall and is quite resistant to unfavorable conditions. The zygospore will later germinate under favorable conditions. It undergoes meiosis, germinates to produce sporangium which release spores. Each spore can germinate and continue the life cycle.

Asexual Reproduction in Rhizopus

2009-12-29T20:04:00.000+05:00

Asexual reproduction takes place by the production of large number of spores within the sporangia. Immature sporangia are white while mature are black. The spores are thick-walled and non-motile. Each sporangium is borne on a sporangiophore. The tip of the sporangiophores swells and many nuclei migrate to this swelling. The central portion of the sporangium becomes separated from the peripheral zone by the deposition of the dome shaped wall. This doom-shaped wall is called columella. Numerous spores are formed within the sporangium. The outer wall of the sporangium breaks down and spores are displaced by air currents. On a suitable spore germinates and develops into new hyphae.

Rhizopus (black mold or common bread mold)

2009-12-29T19:51:00.000+05:00

Rhizopus is the common bread mold. It is of worldwide distribution. This mold grows well on moist bread and fruits. The plant body or mycelium consists of branched hyphae. Hyphae are non-septate. Each hypha is multinucleated. It has a cell wall composed of chitin. Reserve food is present in the form of glycogen. Hyphae are of several kinds. Root like hyphae called rhizoids anchor the fungus, secrete digestive enzymes and absorb nutrients. Other hyphae called stolons grow to form a network over the surface of the food.
The stolons give rise to still another type of hyphae that grow upward from the surface of the food. These hyphae bear sporangium at the tip and are called sporangiophores. Sporangium is sac-shaped structure having spores in it.

Fungi

2009-12-24T14:27:00.000+05:00

Fungi are extremely diverse group of organisms. There are about 80000 species in this group. Fungi are eukaryotes. They lack chlorophyll and as such they are unable to manufacture their own food and consequently lead a saprophytic or parasitic existence. The saprophytes live on non-living organic matter, causing it to decay; the parasites infect mostly plants or sometime animals causing disease. The plant body is typical filamentous and is composed of thread like structures called hyphae. The mass of hyphae is called mycelium. The hyphae contain nuclei and cytoplasm and are either divided into cells by cross wall (septate) or lack cross walls (non-septate). In the majority of fungi the chief component of cell wall is chitin. Cellulose is absent in the cell wall of most fungi. True fungi are divided into following main groups:
The conjugating fungi, the water molds, the sac fungi, the club fungi and imperfect fungi. Slime molds are also commonly included in kingdom fungi. The study of fungi is called mycology.
Two kinds of reproduction are found in fungi, asexual and sexual. Among the methods of asexual reproduction are (1) fragmentation in which the mycelium breaks into pieces and each fragment is capable of growing into a new individual; (2) budding, in which a small outgrowth called bud is produced in the yeast, and (3) spore production which is the most common type of asexual reproduction. Sexual reproduction is highly varied but always involves the fusion of two haploid nuclei and meiosis. Most fungi reproduce both sexually and asexually. Asexual reproduction is generally more important for the propagation of species.

Comparative Biochemistry

2009-12-06T20:34:00.000+05:00

When two lineages first diverge from common ancestors; the genes and proteins of the lineages are nearly identical. But as time goes by, each lineage accumulates giving changes which lead to RNA and protein changes. Many changes are neutral i.e. not tied to adaptation and accumulate at a fairly constant rate; such changes can be used as a kind of molecular clock to indicate relatedness and evolutionary time. It is possible to examine and compare the RNA nucleotides sequences of ribosome etc to determine the evolutionary relationship between the organisms.

Need For Classification

2009-11-26T18:37:00.000+05:00

About two millions species of living organisms have been identified and biologists speculate that several millions more species remain to be identified. In order to organize these life forms, so that we can study them effectively, communicate knowledge about them, we need a system of classification. Any group used for classification purpose is called a taxon (plural taxa). Taxonomy (Greek = Tasso, arrange, classify and nomos, usage, law) is the branch of biology concerned with identifying and naming of organisms. Modern classification is often referred to as systematic comparative biology because it based on evolutionary relationship. The person who studies taxonomy is called taxonomist or systematist (somebody who classifies organisms according to a taxonomic system).

Homology

2009-11-26T18:33:00.001+05:00

Homology (Greek: Homologous – agreeing) is character similarity that stems from a common ancestry. Comparative anatomy, including embryological evidence provides information regarding homology. The forelimbs of vertebrates are homologous because they contain the same bones organized in the same general way as in a common ancestor. Homologous structures are related to each other through common descent, although they may now differ in their structure and function. In contrast analogous structures have the same function in different groups but not derived from the same organ in a common ancestor. The wings of an insect and the wings of a bat are analogous structures.

An Idea Taxon is Monophyletic

2009-11-26T18:32:00.001+05:00

If all the subgroups within any taxon share the same common ancestors, the grouping is referred to as monophyletic (Greek: Monons, one, and phyle, tribe). Monophyletic taxa are therefore natural groupings because they represent true evolutionary relationships and include all close relatives. A taxon containing a common ancestor and all the taxa descended from it is called a clade. The relationship of clades to each other maybe represented in a branching diagram called a cladogram.

Systematists rely on homology, comparative biochemistry, cytology and genetics in order to determine monophyletic groups.

Bases of Biological Classification

2009-11-26T18:31:00.000+05:00

Classification of groups of organisms allows one to construct a phylogenetic tree, a diagram that indicates common ancestors and lines of descent. In order to classify organisms and to construct a phylogenetic tree, it is necessary to determine the characters of the various taxa groups.

Why atoms form chemical bonds?

2009-11-17T18:50:00.000+05:00

Thousands of things are found in this world. These things are formed by the variety of ways. Except noble gases, which exist as atoms, all other elements and compounds exist as combination of atoms. For example, both oxygen and nitrogen exist as diatomic molecules. Similarly, sodium atoms are firmly joined together in solid sodium metal. In the same way two atoms are held together in the molecules of carbon monoxide (CO). The attractive force, which keeps the atoms together in substances, is called a chemical bond.

Why atoms combine together? The answer to such basic question is both simple and straight forward.

In this world, everything has a tendency to lower its energy. Water flows from higher level to lower level. Similarly, electricity flows from higher potential to lower potential. Why is it so? This happens because both water and electricity are trying to decrease their energy. Atoms, in the same way, also have a tendency to decrease their energy. They can do this by combining with other atoms. It is a natural phenomenon because it increases the stability of atoms.

How atoms succeed in lowering their energy? The early chemists had started thinking about this a long time before. They finally succeeded to get an answer only when the noble gases (He, Ne, Ar, Kr, Xe) were discovered. Helium has two electrons in its outer shell while all other noble gases have eight electrons in their outermost shells. We also know about these gases that neither their atoms combine with themselves nor with other atoms. The probable reason for this lack of reactivity was their stability. It was suggested that these gases were stable due to the presence of eight electrons in their outermost shell. This gave rise to a principle that having eight electrons in the outermost shell meant stability and hence no reactivity as well. This principal was named as Octet Rule.

This discovery of Octet Rule was followed by another similar suggestion that atoms form bonds because they would like to lower their energy by completing their octets. For example, for sodium atoms it is easy to lose one electron and stabilize itself than to gain seven electrons while completing its octet. Sodium atom, therefore, adopts the energetically easier path and loses its electron to form a bond with chlorine atom.

Although, in the beginning, octet rule played a significant role in understanding the nature of a chemical bond, yet further investigation found to be less important.

Let us think about the difference ways the chemical bonds are formed? When atoms of different substances approach each other, there are two possibilities. They may attract or repel each other. If the forces of attraction between them dominate the forces of repulsion, the energy of the system gets lowered and as a result the two atoms will react to form a new molecule. Conversely, the two atoms simply move away from each other.

A chemical bond is thus a force of attraction between atoms, which holds them together in the form of molecule or a compound.

Silver Plating

2009-11-09T21:53:00.002+05:00

1) Anode is made pure silver. 2) When electric current is passed through the electrolyte Ag+ ions migrate towards the cathode and deposit after picking up electrons. Cyanide ions move towards the anode, where they react with silver to form AgCN which combines with KCN to produce the electrolyte K [Ag (CN) 2].

Why is electroplating done?

2009-11-09T21:53:00.001+05:00

The first reason for doing electroplating is decoration. Noble metals like gold and silver etc are deposited on inferior metals to enhance their beauty. The second reason is protection. Inferior metals can be protected from rusting and from the reaction of organic acids. The third reason is repairing. With the help of this process, the broken parts of machinery can be repaired/welded.

Process of electroplating

2009-11-09T21:52:00.000+05:00

The object to be electroplated is first cleaned sand and then washed with caustic soda solution and finally with water. The article is made the cathode, while the metal to be deposited is made anode. The electrolyte is the salt of metal being deposited. The electroplating is carried out in a tank made of glass, wood, cement etc. It is called an electrolytic tank. Electric current is passed through this tank and a thin layer of metal is deposited after sometime on the article.

Electroplating

2009-11-09T21:51:00.001+05:00

It is a process in which a metal is deposited on another metal with the help of electrolysis.

Recharging

2009-11-09T21:50:00.000+05:00

The process in which dilute sulphuric acid which is produced during discharging is made reversible is called recharging.

Lead Storage Battery

2009-11-08T20:45:00.000+05:00

: It’s a common automobile battery, also known as accumulator. It is usually of 12 volts. The voltage depends on the number of cells used. Galvanic cells are connected in series in this battery. Electrodes are used and one electrode is made of lead Pb, while the other is made of lead oxide PbO2. Dilute sulphuric acid is used as electrolyte. When the external circuit is complete and the battery is in running condition, the following oxidation-reduction reaction occurs.
H2SO4------->2H+ + SO4 2-
Reaction at anode: Pb + SO4 2- --------> PbSO4 + 2e-
Reaction at cathode: PbO2 + 4H+ + SO4 2- + 2e ------>PbSO2 + 2H2O

Zinc-Carbon dry cell

2009-11-08T20:42:00.002+05:00

In this cell chemical energy is used to produce electric current.
Construction: It has a protective cover of car-board or a metal, which protects it from the environment. It has a zinc container inside the cover which works as anode. Inside the zinc container, the mixture of ammonium chloride, manganese dioxide powdered carbon is filled. A graphite rode is placed in the center of this paste which acts as cathode. The cell is made waterproof using wax, shellac or any other such material. When the circuit is complete, the following reaction takes place.
Reaction at anode: Zn ---------> Zn2+ + 2e-
Reaction at cathode: 2MnO2 + 2NH4+ + 2e----->Mn2O3 + 2NH3 + H2O
Ammonium produced at anode reacts with zinc ions to produce [Zn(NH3)4]2+ ions.

Electrochemical Cells

2009-11-08T20:42:00.001+05:00

These are the cells in which chemical energy is used to produce electric current.
We know that oxidation-reduction reaction take place at the electrode when fused ionic compounds or the aqueous solutions of ionic compounds are electrolyzed. These oxidation-reduction reactions are used in cells to produce electricity.

Electrochemical Series

2009-11-08T20:41:00.002+05:00

A list of ions in which they are arranged in order of their ability to get discharged is called electrochemical series.
Explanation: The series tells us that which ion will preferably discharged during electrolysis when the solution contains two or more ions.
Example: Suppose a solution contains bromide (Br-) and iodide (I-) ions is electrolyzed. During the electrolysis process, the iodine ions are discharged first while the bromine ions remain in the solution. It’s because the iodine ions below the bromide ions in the series.

Faraday’s Second Law of Electrolysis

2009-11-08T20:41:00.001+05:00

When same quantity of electricity is passed, for the same time, through different electrolytes connected in series, the substances deposited at the electrode will be in ratio of their chemical equivalents.
Electrochemical Equivalent = Quantity of substance deposited/Quantity of electricity passed (Q)

Knowledge Class

Proteins

Qatar Airways INTERNATIONAL

DELL - IT COMPANY

World Bank

IMPORTANCE OF CARBON

CONDENSATION AND HYDROLYSIS

WATER

INTRODUCTION TO BIOCHEMISTRY

THE IMMUNE SYSTEM

THE LYMPHATIC SYSTEM

CARDIOVASCULAR DSORDERS

BLOOD PRESSURE

Rate of Blood Flow

Flow of Blood in the Vein

﻿The Blood Vessels

The Heart in Action

The Heart

Function of Blood

Blood Cells and Cell like Bodies

Plasma

Blood

Transportation In Man

Evolution of Vertebrate Heart -- Birds and Mammals

Evolution of Vertebrate Heart – Reptiles

Evolution of Vertebrate Heart – Amphibians

Evolution of Vertebrate Heart – Fish

Vertebrate Blood Circulatory System

Transportation in Cockroach

Transportation in Earthworm

Types of the Circulatory System

General Characteristics of a Blood Vascular System

Circulatory System

Transportation in Planaria

Transportation in Hydra

Transport In Animals

Critical Amendments Of Pressure Flow Hypothesis

Pressure Flow Mechanism

Phloem Parenchyma, Fibers and Sclereids

Companion Cell

Sieve Tube

Features Of Phloem In Relation To Their Transport

Translocation of Organic Solutes

Transpiration as a Necessary Evil

Factors Affecting Transpiration

Opening and Closing of Stomata

Structure of Stomata

Stomata

Stomatal Transpiration

Lenticular Transpiration

Cuticular Transpiration

Types and Mechanism of Transpiration

Transpiration

Incipient Plasmolysis

Deplasmolysis

Plasmolysis

Pressure Potential Ψ s

Solute Potential Ψ s

Advantages Of Using Water Potential

Water Potential (symbol Ψ, The Greek Letter Psi)

Osmosis

The Vacuolar Pathway

The Symplast Pathway

The Apoplast Pathway

Uptake Of Water By Roots

Facilitated Diffusion

Active Transport

Transport In Plants

Need For Transportation

Transportation

Virtual Grassland Picture

Air And Water As Respiratory Medium

Need of Respiratory Gas Exchange

The Kingdom Animalia

EVENTS OF THE MITOSIS

Cell Division - MITOSIS

Chromosomes - Their Organization

Reproduction of Cells

Harmful Effects of Fungi

Beneficial effects of Fungi

The Blood Vessels