NCERT Solutions Curiosity Chapter 13 Sexual reproduction in animals — In-text Questions

Book page 223 Updated on2026-09-05

Q1.

What are the advantages and disadvantages of giving birth to young ones vs. laying eggs?

Answer

Both are solutions to one problem — how to feed and protect a developing embryo. Each buys safety at a different price.

	Giving birth to young ones	Laying eggs
Advantages	The embryo develops inside the mother, so it is protected from weather, predators and drying out. Food and oxygen are supplied continuously, so the young one can be born at a well developed stage.	The mother is not carrying the young, so she can move, feed and escape normally. Many eggs can be produced at one time, and in water thousands can be released at once.
Disadvantages	Only a few young at a time. The mother carries the weight and the cost, and the long development ties her to it. If the mother dies, the young die with her.	All the food for the whole of development has to be packed into the egg in advance. Once laid, the egg is exposed — many eggs are eaten or destroyed, so most never hatch.

Why it happens: Notice the trade-off: internal development spends a great deal of care on very few offspring, while egg laying spends very little on very many. Both work, and which one succeeds depends on the surroundings. In water, where eggs and gametes can simply be released together, laying thousands is efficient; on land, where an embryo would dry out, keeping it inside or sealing it in a shell is the safer route.

Q2.

Do you think animals like dogs, cows, or humans could lay eggs like birds? Why or why not?

Answer

No, they could not. Laying eggs is not a choice an animal makes; it is the way its whole body is built, and that is fixed by the instructions it inherits.

Three reasons, in order of how deep they go:

The body has no machinery for it. A hen's body forms a large egg loaded with enough food for the entire development of the embryo, and then wraps it in a shell. A dog, a cow or a human makes a tiny egg cell with almost no stored food, because the food is meant to come later, from the mother's body.
The nutrition strategy is the opposite one. In mammals the zygote develops inside the female and the mother's body provides all the food and oxygen the baby needs until it is born. An egg laid outside would have no such supply.
The instructions cannot be swapped. A calf grows into a cow because it inherits the complete set of cow instructions. Reproduction can pass on small changes, and over many generations these can add up — but no single generation can be handed a different body plan.

Why it happens: Reproduction copies and reshuffles the instructions a parent already has. It does not invent new ones to order. A whole new way of reproducing would require a very large number of coordinated changes, and those appear, if at all, only over enormous stretches of time.

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