DAV Class 8 Science Chapter 14 Question Answers
Reproduction is the one thing every living species has to get right, and Chapter 14 of the DAV Class 8 Science book explains how animals manage it. This article gives you the answers to every exercise in the chapter, plus the extra practice questions, written in plain language so you can understand the idea behind each answer and put it in your own words in the exam.
Quick revision before you start
Animals reproduce in two broad ways. In asexual reproduction, one parent is enough, no gametes are involved, and the young ones are copies of the parent. Amoeba splits in two (binary fission), while Hydra and yeast grow a small bud that later separates (budding). In sexual reproduction, two parents each make a special cell called a gamete. The male gamete is the sperm and the female gamete is the egg (ovum). When the two fuse, that is fertilisation, and the result is a zygote, which divides again and again to become an embryo and eventually a foetus.
Fertilisation can happen outside the body (external, as in frogs and fish) or inside the body (internal, as in humans, birds and crocodiles). Animals that lay eggs are oviparous. Animals that give birth to live young are viviparous.
Something to Know
A. Fill in the blanks
1. Genetically identical individuals are produced by asexual reproduction.
2. Gametes are the specialised cells that take part in sexual reproduction.
3. An animal that produces both male and female gametes is called a hermaphrodite.
4. A fertilised egg is also known as the zygote.
5. The incubation period of a hen’s egg is 21 days.
B. Match the following
| Column I | Column II |
|---|---|
| (1) Hydra | (c) Budding |
| (2) Reptiles | (d) Oviparous |
| (3) Earthworm | (a) Hermaphrodite |
| (4) Gills | (e) Tadpole |
| (5) Egg shell | (b) Calcite |
A tadpole breathes through gills, which is why gills go with it. An earthworm has both male and female reproductive organs, so it is a hermaphrodite.
C. Tick the correct option
1. The site of fertilisation in humans is the: (b) Oviduct. The egg travels down the oviduct after leaving the ovary, and this is where the sperm meets it.
2. Why does a parrot not belong to the same group as monkey, man and cat? The idea behind the question is simple. Monkey, man and cat give birth to live young (viviparous), while a parrot lays eggs (oviparous). The answer key marks option (a), but the printed options in many copies of this question are badly worded, so read your own book’s options and pick the one that says the parrot is the odd one out because it lays eggs.
3. An organism that reproduces by budding is: (c) Yeast. Amoeba divides by binary fission, and Spirogyra reproduces by fragmentation.
4. A caterpillar develops into a silk moth through: (b) Metamorphosis.
5. A foetus can best be defined as: (c) A well-developed embryo.
D. Answer in brief
1. Distinguish between asexual and sexual reproduction.
| Asexual reproduction | Sexual reproduction |
|---|---|
| Only one parent is involved. | Two parents are involved. |
| No gametes are formed. | Male and female gametes are formed. |
| It is a quick process. | It is a slower process. |
| Offspring are identical to the parent. | Offspring show some variation from the parents. |
2. How does reproduction take place in Hydra? Hydra reproduces by budding. A small outgrowth appears on the parent’s body, grows into a tiny Hydra and then breaks off.
3. How is fertilisation in a hen different from that in a frog? In a hen, fertilisation happens inside the body (internal fertilisation). In a frog, the eggs and sperm meet in water outside the body (external fertilisation).
4. State the difference between oviparous and viviparous animals. Oviparous animals lay eggs, and the young ones hatch outside the mother’s body. Viviparous animals give birth to fully formed young ones.
5. Why do frogs lay far more eggs at a time than hens? A frog lays its eggs in water, where they are easily eaten by other animals or washed away. Many never survive to become tadpoles, so the frog must lay thousands to make sure a few do. A hen lays a small number of eggs on land and sits on them to keep them warm and safe, so far more of her eggs survive.
6. How do you differentiate between a zygote and an embryo? A zygote is a single cell, formed when the sperm and egg fuse. An embryo is made of many cells, formed after the zygote divides repeatedly.
7. A mother gives birth to the child. How does the child get features of both parents? Both parents pass genes to the child through their gametes. The sperm carries the father’s genes and the egg carries the mother’s genes, and the child inherits a mix of both.
E. Answer the following
1. Define metamorphosis. List the changes a tadpole undergoes to become a frog.
Metamorphosis is a clear and fairly rapid change in the body structure and way of life of an animal during its life cycle. In a tadpole, the changes happen in this order. Hind legs appear first, followed by front legs. Lungs develop so that the young frog can breathe air, and it begins to rise to the surface to gulp air. The long intestine becomes shorter as the diet shifts to a meat-based one. Finally, the tail is absorbed into the body, and the tadpole becomes a young frog.
2. Trace the events that lead to the development of a chick from the fertilised egg of a hen.
After fertilisation, the zygote starts dividing while it travels down the oviduct. As it moves, protective layers form around it, and the hard egg shell is one of them. The egg is then laid, and the embryo develops inside it for about 21 days while the hen keeps it warm. At the end of this period the shell cracks and the chick comes out.
3. Where does fertilisation occur in human beings? How does the zygote develop into an infant?
Fertilisation takes place in the oviduct of the female. The zygote divides into two cells, then four, and keeps dividing over the next few days until it becomes a ball of cells called the embryo. The embryo moves into the uterus and attaches itself to the uterine wall, which is called implantation. It keeps growing and developing, and once the main body parts have formed and it looks like a human baby, it is called a foetus. After about 40 weeks of pregnancy the baby is fully developed and ready to be born.
4. Draw a neat, labelled diagram of the human sperm and explain how its shape and size help it function.
Draw a tiny tadpole-like cell with three parts, and label them clearly: the head (with the nucleus, and a cap-like structure at the tip), the middle piece, and the tail. Here is how the structure helps. The head carries the father’s genetic material, and the tip releases an enzyme that helps the sperm break through the outer layer of the egg. The middle piece supplies the energy for movement. The long tail lashes from side to side and pushes the sperm forward. The sperm is very small and light, which lets it swim quickly through the female reproductive tract.
5. Draw labelled diagrams of the human female and male reproductive systems.
For the female system, draw and label the two ovaries, the two oviducts (also called fallopian tubes), the uterus, and the vagina. For the male system, draw and label the two testes inside the scrotum, the sperm ducts, the urethra, and the penis. Keep the labels in a straight line on one side with neat pointer lines, because examiners give marks for clear labelling.
6. Write the functions of the following parts of the human female reproductive system.
(a) The ovaries produce the eggs. (b) The oviduct is where fertilisation takes place. (c) The uterus is where the embryo gets implanted and grows into a foetus.
Value Based Question
Atul’s mother wanted to clean the garage, but the maid found a pigeon’s nest in one corner with a few eggs in it. Atul asked that the nest be removed only after three weeks, and his mother agreed.
1. Why did Atul ask the maid to wait for 3 weeks? He knew the eggs would need about three weeks to hatch into chicks, and removing the nest earlier would destroy them.
2. What is the egg shell made of? Calcite, a form of calcium carbonate.
3. What values did Atul show? Kindness and concern for animals, along with awareness and responsibility towards living creatures.
Something to Do
1. Twins, triplets and quadruplets. This is a hospital visit activity, so the answer will come from your own enquiry. A useful point to include: twins can develop from one fertilised egg that splits into two, or from two separate eggs fertilised at the same time. Babies born in multiple births are often smaller and need extra medical care, so their chances of survival depend a lot on the care they get.
2. Egg-laying mammals. The platypus and the echidna are mammals that lay eggs. They also feed their young with milk, which is why they still count as mammals.
3. Five common birds in your city. This is a project question. Pick birds such as the house sparrow, crow, pigeon, myna and koel, and note down the nest type, the usual season for eggs, the number of eggs, the incubation period and what the eggs look like.
4. Dolly the sheep. Dolly was the first mammal cloned from an adult cell. She was produced in Scotland in the 1990s by scientists at the Roslin Institute, by placing the nucleus of an adult cell into an egg whose own nucleus had been removed. Other cloned animals include cattle, goats, pigs and dogs.
5. Complete the table. The exact figures vary from source to source, so the values below are commonly accepted averages. If your teacher has given you different figures from the book, write those in your answer.
| Animal | Young one | Approximate time of development | Approximate lifespan |
|---|---|---|---|
| Lion | Cub | About 110 days | 10 to 15 years in the wild, longer in captivity |
| Cow | Calf | About 280 to 290 days | About 20 years |
| Horse | Foal | About 340 days | 25 to 30 years |
| Elephant | Calf | About 22 months | 60 to 70 years |
| Goat | Kid | About 150 days | 15 to 18 years |
| Kangaroo | Joey | About 33 days before birth, then months in the pouch | 8 to 12 years in the wild |
| Cat | Kitten | About 64 days | 12 to 18 years |
| Dog | Puppy | About 63 days | 10 to 13 years |
| Whale | Calf | About 10 to 12 months | Blue whale: 80 to 90 years |
Important questions and extra practice
I. Fill in the blanks
1. Amoeba reproduces by binary fission.
2. Yeast reproduces by budding.
3. Hydra reproduces by budding.
4. A single parent is involved in asexual reproduction.
5. Two parents are involved in sexual reproduction.
6. Sperm are produced by the testes.
7. Eggs are produced by the ovaries.
II. Tick the correct answer
1. How many types of gametes are formed in asexual reproduction? (d) Zero.
2. How many types of gametes are formed in sexual reproduction? (b) Two, the male gamete and the female gamete.
3. Which animal shows external fertilisation? (a) Frog.
4. Which of these is oviparous? (d) Eagle. Chimpanzee, rat and human are all viviparous.
5. How many ovaries are in the female reproductive system? (b) Two.
6. Which organ works as a passage for semen? The answer key gives (c) Penis, since semen leaves the body through it. Remember that the sperm ducts carry sperm from the testes towards the urethra, so read the question carefully in your own book.
III. Answer the following
1. What is asexual reproduction? It is a type of reproduction in which a single parent produces young ones without forming gametes.
2. What is sexual reproduction? It is reproduction in which two parents are involved. The male parent forms sperm and the female parent forms eggs, and the two gametes fuse in a process called fertilisation.
3. Explain binary fission. Binary fission is seen in single-celled organisms such as bacteria and Amoeba. The parent cell simply divides into two equal daughter cells, and each grows into a new individual.
4. What are gametes? Gametes are the special cells formed by the male and female parents for sexual reproduction. In animals, the male gamete is called a sperm and the female gamete is called an egg or ovum.
5. What types of fertilisation are seen in animals? There are two. In external fertilisation, the sperm and egg fuse outside the body, as in frogs and fish. In internal fertilisation, they fuse inside the female’s body, as in humans, birds and crocodiles.
6. What is external development? It means the embryo grows outside the mother’s body, usually inside an egg. It is the normal pattern when fertilisation is external, and it also happens in egg-laying animals that have internal fertilisation, such as birds.
7. Explain the structure of a sperm. A sperm has three parts: a head, a middle piece and a tail. The head contains the nucleus, and a structure at its tip releases an enzyme that helps the sperm enter the egg. The middle piece gives energy, and the tail helps the sperm swim.
IV. Projects
1. List 10 animals that show external fertilisation. Frog, toad, salmon, carp, rohu, catla, goldfish, seahorse, starfish and sea urchin.
2. List five animals that show metamorphosis. Frog, silk moth, butterfly, housefly and mosquito.
Common mistakes students make in this chapter
Many students mix up zygote, embryo and foetus. A simple way to remember: the zygote is one cell, the embryo is a ball of cells, and the foetus is the stage when it begins to look like a baby.
Another common slip is confusing oviparous with viviparous. Oviparous animals lay eggs (ovi means egg), and viviparous animals give birth to live young.
In diagram questions, students often forget labels or draw the parts out of proportion. Draw with a sharp pencil, keep it neat and label every part you can.
Frequently asked questions
Where does fertilisation take place in humans?
Fertilisation takes place in the oviduct of the female reproductive system.
What is the difference between internal and external fertilisation?
In internal fertilisation, the sperm and egg meet inside the female’s body. In external fertilisation, they meet outside the body, usually in water.
How long does a hen’s egg take to hatch?
About 21 days of incubation.
Why do animals that lay eggs in water produce so many eggs?
Because many eggs are eaten or washed away, so a large number are needed for a few to survive.
Written for students following the DAV Science book for Class 8. Please cross-check any figures with your own textbook and teacher.