The Process of Sexual Reproduction and Development

Sexual reproduction is a process that involves the fusion of two sets of DNA to form a zygote, which eventually develops into an adult organism through a series of changes known as development. During development, the zygote undergoes various transformations to become a mature individual.

Embryology: The Study of Embryo Development

The stage of the multicellular organism that develops from a zygote is called an embryo. In seed plants, the embryo is part of the seed. The study of embryo development is called embryology, which is a fascinating field of biology that explores how embryos grow and develop.

Growth and Development: An Interconnected Process

Growth is a fundamental characteristic of all living organisms, and it is closely linked with development. The phrase "growth and development" is commonly used to describe the processes that are normally thought of as growth. Development involves an increase in complexity, while growth refers to the permanent and irreversible increase in size that occurs in an organism.

Phases of Growth in Multicellular Organisms

Starting with an individual cell, the growth of a multicellular organism can be divided into three phases: cell division, cell enlargement, and cell differentiation.

Cell Division: An Increase in Cell Number

During the first phase of growth, cell division occurs through the process of mitosis, resulting in an increase in cell number.

Cell Enlargement: An Irreversible Increase in Cell Size

In the second phase of growth, cell enlargement occurs through the uptake of water or the synthesis of living material, resulting in an irreversible increase in cell size.

Cell Differentiation: Specialization of Cells

The third phase of growth is cell differentiation, which involves the specialization of cells in their functions. This phase of cell development is also included in the broad sense of growth.

In conclusion, growth and development are two interconnected processes that occur in all living organisms. Embryology is a fascinating field that explores the development of embryos, which are the early stages of multicellular organisms. The growth of a multicellular organism can be divided into three phases, including cell division, cell enlargement, and cell differentiation, each with its unique characteristics.