NCERT 8th Class (CBSE) Science: Reproduction

Question: How does fertilization occur in frogs?

Answer: A frog passes through three stages during its development from an egg to an adult frog:

Egg → Tadpole (larva) → adult frog

The tadpole that hatches out of the egg looks very different from an adult frog. It undergoes changes to finally become a frog.

Question: What happen in the female body if the ovum is not fertilized by a sperm.

Answer: If the ovum is not fertilized by a sperm, it is expelled from the uterus along with some uterine muscles and blood. This is known as menstruation.

Question: How does Hydra reproduce?

Answer: Yeast and Hydra reproduce by budding. In Hydra, a bud appears on the body wall which grows into full Hydra in a day or two and separates from the parent.

Question: Explain the difference between viviparous and oviparous animals.

Answer: Viviparous animals

1. The animals that give birth to young ones are called viviparous animals. Example: Except platypus all mammals.
2. Embryo is developed inside the mother’s womb.

Oviparous animals

1. The animals that lay eggs are called oviparous animals. Examples: Fishes, birds.
2. Embryo is developed inside a hard shell outside the mother’s body. Example: Hen’s egg.

Question: Explain what happens after a hen lays a fertilized egg.

Answer: After fertilization, the zygote divides repeatedly and travel down the oviduct as in humans. However, as it travels down, many protective layers are formed around it. The hard shell of a hen’s egg is one such layer. After the hard shell is formed around the embryo, the hen lays the egg. The hen then sits on the egg to keep it warm. Development of the chick takes place inside the shell. It takes about 3 weeks for the embryo to develop into a chick. After its development is complete, the chick comes out by bursting open the egg shell.

Question: 1. Give details of two different ways in which a zygote develops in case of animals where fertilization is internal.

Answer: Internal fertilization in earthworm: An earthworm , though a hermaphrodite, does not fertilize itself. Two earthworms come in contact with each other and exchange sperms. The eggs are fertilized internally with the sperms received from the partners. Thus, a zygote is developed.

Internal fertilization in human: In human fertilization takes place on meeting of male and female gamete inside
body. Fertilization is internal, and the development of the zygote into a fully formed individual also occurs inside the
body of the female.