Internal Fertilisation In Hen
Internal Fertilisation In Hen
The hen is a bird. Internal fertilisation takes place in hen also. But a hen does not give birth to chicks (like human beings give birth to babies). We will now describe how chicks are born.
(i) After fertilisation takes place inside the body of the hen, the fertilised ege (or zygote) divides repeatedly to form embryo which travels down the oviduct.
(ii) 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 (other protective layers being inside the egg shell).
(iii) 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.
(iv) The hen then sits on the eggs to provide sufficient warmth to the eggs for the development of the embryo into the chicks. The embryo takes about 3 weeks (21 days) to develop into a complete chick. The development of the chick from egg takes place inside the hen's egg during this period (see Figure 13).
(v) After the chick is completely developed, the egg shell breaks open automatically and the chick comes out of it. This is how a chick is born.
During its development into chick, the embryo gets all its food from the egg yolk. The albumen present in egg helps to protect the embryo from damage. The embryo obtains oxygen by the diffusion of air through the egg shell and other membranes. The embryos of all the birds and reptiles, etc., develop in the same way (like that of hen) inside their shelled eggs.
In animals (such as frogs, fish, etc.) which undergo external fertilisation, development of the embryo takes place in the eggs, outside the female body. In such animals, the embryos continue to grow within the egg coverings. After the embryos develop into complete young ones, the eggs hatch and the alive young ones come out. From this discussion we conclude that:
(i) Some embryos (like those of humans, cats, dogs, etc.) grow inside the mother's uterus till they have completely developed into baby animals, but
(ii) Some embryos (like that of birds, reptiles and insects, etc.) grow inside the eggs which the mother has laid, till they have completely developed into baby animals.
The embryo takes about ________________ to develop into a complete chick. | |||
| Right Option : B | |||
| View Explanation | |||
The embryo obtains ________________________ by the diffusion of air through the egg shell and other membranes. | |||
| Right Option : A | |||
| View Explanation | |||
Which of the following are correct : (a) Some embryos (like those of humans, cats, dogs, etc.) grow inside the mother's uterus till they have completely developed into baby animals, but (b) Some embryos (like that of birds, reptiles and insects, etc.) grow inside the eggs which the mother has laid, till they have completely developed into baby animals. (c) All embryos grow inside the eggs which the mother has laid, till they have completely developed into baby animals. | |||
| Right Option : A | |||
| View Explanation | |||
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