Question

Trace the sequence of events that lead to development of a chick from the fertilised egg of a hen.

NCERT Class VIII
Science - Exemplar Problems

Chpater 9. Reproduction in Animals

Answer 1

1)After fertilisation takes place inside the body of the hen, the fertilised egg or zygote divides repeatedly to form embryo which travel down the oviduct.

2)As it travels down the oviduct, many protective layers are formed around the embryo.The hard shell that we see in a hen’s egg is the outermost protective layer.

3)After the hard egg shell is formed around the developing embryo, the hen finally lays the egg.That is , the hen’s egg comes out of its body.

4)The hen then sits on the eggs to provide sufficient warmth to the egg for the development of the embryo into the chicks.The embryo takes about 3 weeks to develop into a complete chick.The development of the chicks from egg takes places inside the hen’s egg during this period.

5)After the chick is completely developed, the egg shell breaks open automatically and the chick comes out of it.

The embryo gets all its food from the egg yolk.The albumen present in the egg helps to protect the embryo from damage.The embryo obtains oxygen by the diffusion of air through the egg shell and other membrane.

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Answer 2

Explanation:

Fertilization is fusion of male and female gamete. Immediately after fertilization, the embryological process that transforms single celled zygote into a hollow spherical multicellular blastula is referred to as cleavage. Cells of the blastula undergo gastrulation and form and segregate specific layers of tissue, called germ layers. The embryological strcture with three germ layers is termed as gastrula. These three germ layers then divide and differentiate into various organs. Correct sequence of events is fertilization, cleavage, gastrulation and differentiation.

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