Growth and Development

Growth: it is the increase in the number of cells. It is a permanent increase in size. (Do you think that getting fat can also be called growth?). Growth refers to features that can be measured, example:
 

1. Increase in mass: dry or wet mass of a plant (Growth or not?        A seed in water increase in mass)

2. Increase in height:  e.g. human height, height of plant shoot

3. Increase in surface area: e.g. leaves ( note: puffer fish increase in size to scare predators, is this called growth?)

4. Increase in numbers: e.g. increase in number of leaves

Growth can be divided into three stages: (a) cell division   (b) cell enlargement   (c) cell differentiation

Growth in humans: Stages

(a) Infancy and childhood: Rapid development in height. Cell division takes place in all parts of body by mitosis

(b) Puberty: Stage of sexual maturity. Growth continues until adulthood, with increase in height more rapid than increase of weight.

(c) Adulthood: Most adult stop growing from age 20. Some cells continue to divide and form new ones, because old cell have died. For e.g. red blood cells. 

Development: Development is an increase in complexity of an organism as it grows to adulthood e.g. production of sperm and release of egg from puberty onwards. 

NB: Growth and development in animals are controlled mainly by hormones (endocrine system). Recall that pituitary gland is the "master gland" controlling other glands like thyroid gland.