Animal growth

QUESTION -Discuss growth process in animals

ANSWER-

INTRODUCTION

Growth occurs by two main processes: increase in the number of cells and increase in the size of cells.In animals, growth takes place all over the animal's body until it reaches full size. Cells in certain areas, such as the skin, still retain the ability to grow and divide.

Mitosis is the mechansim involved in all these processes, it is the type of cell division1 where 2 new cells are produced from a single cell. The two new cells have the same number of chromosomes as the parent cell and are identical to it and to each other.

Multicellular organisms have a huge variety of different types of cell; humans have around 200 different cell types, all of which are derived from a single fertilised egg cell. New cells produced by mitosis differentiate and become specialised. Each cell type has specific genes "switched on" or "switched off" so that it can carry out its particular function.

PROCESS OF GROWTH

Growth occurs during two periods: prenatal and postnatal. During prenatal growth, cells begin dividing after fertilization. Along with dividing, they begin differentiating. Differentiating is when the cells take on a certain shape and function. Three layers of cells form: the ectoderm (outer layer), the mesoderm (middle layer), and the endoderm (inner layer). The ectoderm forms the brain and nervous system. The mesoderm forms the cardio-vascular system, voluntary muscles, bone, and connective tissue. The endoderm develops into the digestive system.

During postnatal growth, the animal grows in size. This occurs in to stages. The first stage is from birth to ½ the animal’s mature size. During this period, the animal grows fast and efficiently. During the second growth period, growth is slowed. This usually occurs around puberty. The tissues slowly grow until they reach maturity. The skeleton system of the animal grows rapidly after birth. When the bones have begun to mature, the muscles of the animal begin to grow. Finally, after the muscle growth, the animal begins to deposit fat.

Late maturing animals take a longer time to reach their maximum size. This delays the on set of puberty. Their bones grow for a longer period of time. Because of this, it takes longer for the animal to reach their mature size. It also takes more time for the animal to deposit fat. Early maturing animals do not take as long to reach maturity. They enter puberty earlier, and put on muscle and fat at a younger age.