Growth is an irreversible increase in the dry mass of an organism. During growth, there is an increase in the number of cells. This also involves an increase of solid matter, amount of cytoplasm and dry mass. This does not include increases in water content and stored food material because these are not permanent. For example, when a plant cell is placed in a hypotonic solution, there is a net gain of water via osmosis and when placed in a hypertonic solution then, there is a net loss of water. So, this type of increase in the size of the cell is not permanent and so cannot be considered as growth.

Development and growth are inseparable, i.e. it is closely related to growth. Development involves differentiation of cells, an increase in dry mass, i.e. increase in growth and an increase in complexity of an organism. Development implies a change in shape, form or structure resulting in improved working or in functioning. It continues after birth till death. It is influenced by both heredity and environmental factors. Growth and development take place simultaneously, but they are different. For e.g. development in flowering plants consists of the growth of a zygote into an embryo within a seed, the process of germination and the growth of a seedling into an adult plant.

Dry matter refers to the biological mass whose water and stored food which is not permanent are removed. Dry mass is the best measure of growth. Growth refers to the irreversible increase in the size of the body. Dry mass is a more reliable measure of mass than fresh mass because the former excludes the fluctuating water concentrations in the biological material measured which is present in the latter.