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Reproduction, Development and Growth — BIOLOGY STD 8 — Question

ICSE BoardEnglish MediumSTD 8BIOLOGYReproduction, Development and Growth4 Marks
Question
Explain the process of development of a zygote into a foetus.
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Answer

The process of formation of an individual from the basic unit of life, that is, zygote $($in plants it is a seed or any body part$)$ is called development. In humans the zygote after reaching the uterus begins to divide to form many more cells and becomes a ball of cells. This gets attached to the wall of the uterus for further development. The time between fertilization and birth is called pregnancy, which lasts for around $280$ days or $9$ months.

From the third week of development till the end of the second month the developing organism is called an embryo. The embryo is attached to the uterus by a special structure called placenta. Through the placenta, materials like nutrients and oxygen pass from the mother to the embryo but the blood of the mother and embryo do not mix.

Carbon dioxide and other wastes from the embryo pass to the mother’s blood through the placenta. The embryo is connected to the placenta through a cordlike structure called the umbilical cord. The embryo is surrounded by a sac$-$like membrane called amnion and it is filled with a fluid called amniotic fluid. This acts like a cushion and protects the growing embryo. The ball of cells undergoes many cell divisions.

The cells change their size, shape and turn into particular types of cells performing specific functions, such as nerve cells and blood cells. This is called cell differentiation. From these differentiated cells, tissues and organs develope which get organized and finally develop to form a new individual. From the beginning of the third month until birth the developing baby is called a foetus.

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