Transport of Molecules across the Plasma Membrane

The plasma membrane serves as a selectively permeable barrier, allowing some molecules to pass through while preventing the passage of others. It is also known as a differentially permeable membrane due to its ability to regulate the movement of substances in and out of the cell.

Molecules can cross the plasma membrane through passive or active processes. Passive processes, such as diffusion and osmosis, do not require energy, while active processes, including active transport, exocytosis, and endocytosis, require ATP molecules as a source of energy.

How molecule cross plasma membrane

Active transport involves the movement of molecules or ions against their concentration gradient, resulting in their accumulation either inside or outside the cell. For example, glucose is absorbed from the gut by cells lining the digestive tract through active transport, as molecules move from an area of lower concentration to an area of higher concentration, opposite to the process of diffusion.

Active transport

 

Endocytosis is a process where cells take in substances by forming vesicles. 

           

Exocytosis is a process where vesicles, often formed by the Golgi bodies, carry specific molecules and fuse with the plasma membrane, releasing their contents outside the cell. For example, insulin is secreted from insulin-secreting cells through exocytosis.

Phagocytosis is a type of endocytosis that occurs when large materials, such as food particles, are engulfed by the cell. Examples of phagocytosis include Amoeba engulfing Paramecium and macrophages engulfing bacteria and worn-out red blood cells in mammals.

Phagocytosis