Reproduction in Animals
Welcome to HSLC Guru! This chapter on Reproduction in Animals from the ASSEB Class 8 General Science textbook explores how living organisms produce their offspring and continue their species. You will learn about the two main modes of reproduction — sexual and asexual — along with the male and female reproductive organs, the formation of gametes, fertilisation, development of the zygote, and fascinating processes like metamorphosis and cloning. This complete English-medium guide includes a detailed summary, textbook question answers, additional practice questions, and a glossary to help you master the chapter with confidence.
Summary
Modes of Reproduction: Reproduction is the biological process by which living organisms produce new individuals of their own kind. It ensures the continuation of species. There are two main modes of reproduction in animals — sexual reproduction and asexual reproduction. In sexual reproduction, two parents (male and female) are involved, and the offspring are produced by the fusion of male and female gametes. In asexual reproduction, only one parent is involved, and the offspring are genetically identical to the parent. Most higher animals reproduce sexually, while many lower organisms like Hydra and Amoeba reproduce asexually.
Sexual Reproduction and Reproductive Organs: Sexual reproduction involves the male and female reproductive systems. The male reproductive organs include a pair of testes (which produce male gametes called sperms), two sperm ducts (vas deferens), and the penis. The female reproductive organs consist of a pair of ovaries (which produce female gametes called ova or eggs), two oviducts (fallopian tubes), and the uterus (womb). A sperm is a small, motile cell with a head, middle piece, and tail, while the ovum is a large, round, non-motile cell. The fusion of sperm and ovum is called fertilisation, which forms a single cell known as the zygote.
Fertilisation and Development: Fertilisation can be of two types — internal fertilisation, which takes place inside the female body (as in humans, cows, dogs, hens), and external fertilisation, which occurs outside the female body in water (as in frogs, fish). The zygote divides repeatedly to form an embryo, which gets implanted in the wall of the uterus. The embryo gradually develops body parts and is then called a foetus. Animals that give birth to young ones are called viviparous animals (humans, cows), while animals that lay eggs are called oviparous animals (hens, lizards, frogs). Some animals undergo a remarkable transformation called metamorphosis, where the young one differs greatly from the adult — for example, a tadpole develops into a frog, and a caterpillar becomes a butterfly.
Asexual Reproduction and Cloning: Asexual reproduction is common in simple organisms. Budding is seen in Hydra, where a small bulb-like projection (bud) grows on the parent’s body and detaches to form a new individual. Binary fission is found in Amoeba, where the parent cell divides into two equal daughter cells. A modern technique called cloning allows scientists to create a genetically identical copy of an animal. The first successfully cloned mammal was Dolly the sheep, born on 5th July 1996 in Scotland. Dolly was created from a single body cell of an adult sheep, marking a major achievement in biotechnology.
Textbook Questions and Answers
1-Mark Questions
Q1. What is reproduction?
Answer: Reproduction is the biological process by which living organisms produce new individuals of their own kind to continue their species.
Q2. Name the two modes of reproduction in animals.
Answer: The two modes of reproduction in animals are sexual reproduction and asexual reproduction.
Q3. What is the male gamete called?
Answer: The male gamete is called sperm.
Q4. What is the female gamete called?
Answer: The female gamete is called ovum or egg.
Q5. Name the organ that produces sperms.
Answer: The testes produce sperms in the male body.
Q6. Name the organ that produces ova.
Answer: The ovary produces ova in the female body.
Q7. What is a zygote?
Answer: A zygote is the single cell formed by the fusion of a male sperm and a female ovum during fertilisation.
Q8. What is fertilisation?
Answer: Fertilisation is the process of fusion of the male gamete (sperm) with the female gamete (ovum) to form a zygote.
Q9. Name the first cloned mammal.
Answer: The first cloned mammal was Dolly the sheep.
Q10. Give one example of an oviparous animal.
Answer: Hen is an example of an oviparous animal.
2-3 Marks Questions
Q1. Differentiate between sexual and asexual reproduction.
Answer: Sexual reproduction involves two parents (male and female), and offspring are produced by the fusion of male and female gametes. Asexual reproduction involves only one parent, and the offspring are genetically identical to the parent. Sexual reproduction produces variation, while asexual reproduction produces identical copies.
Q2. Differentiate between viviparous and oviparous animals with examples.
Answer: Viviparous animals are those that give birth to young ones directly. Examples include humans, cows, dogs, and cats. Oviparous animals are those that lay eggs, which later hatch into young ones. Examples include hens, lizards, frogs, and fish.
Q3. Differentiate between internal and external fertilisation.
Answer: Internal fertilisation occurs inside the female body. Examples include humans, cows, and hens. External fertilisation occurs outside the female body, usually in water. Examples include frogs, fish, and starfish. Internal fertilisation has higher chances of success, while external fertilisation produces a large number of eggs.
Q4. What is metamorphosis? Give two examples.
Answer: Metamorphosis is the process of transformation of a larva into an adult through drastic changes in body structure. Examples — (i) A tadpole develops into a frog. (ii) A caterpillar transforms into a butterfly through the pupa stage.
Q5. Describe binary fission in Amoeba.
Answer: Binary fission is a method of asexual reproduction in Amoeba. The nucleus of the parent Amoeba first divides into two daughter nuclei. Then the cytoplasm divides, and the parent cell splits into two equal daughter cells, each becoming a new individual.
Q6. What is budding? Explain with reference to Hydra.
Answer: Budding is a form of asexual reproduction where a small outgrowth (bud) appears on the parent body. In Hydra, the bud grows by repeated cell division, develops mouth and tentacles, and finally detaches from the parent to live as a new individual.
5-6 Marks Questions
Q1. Describe the male reproductive system in humans.
Answer: The human male reproductive system consists of the following organs:
- Testes: A pair of oval-shaped organs located in the scrotum. They produce male gametes called sperms.
- Sperm Ducts (Vas Deferens): Two tubes that carry sperms from the testes to the penis.
- Seminal Vesicles and Prostate Gland: Glands that secrete fluids to nourish and transport sperms. The mixture of sperms and these fluids is called semen.
- Penis: The external organ that delivers sperms into the female body during reproduction.
Together, these organs work to produce, store, and deliver sperms for fertilisation.
Q2. Describe the female reproductive system in humans.
Answer: The human female reproductive system consists of the following organs:
- Ovaries: A pair of small almond-shaped organs that produce female gametes called ova or eggs.
- Oviducts (Fallopian Tubes): Two tubes that carry the ovum from the ovary to the uterus. Fertilisation usually takes place here.
- Uterus (Womb): A muscular pear-shaped organ where the fertilised egg develops into a baby.
- Vagina: The passage through which the baby is born.
The female reproductive system produces ova, allows fertilisation, supports embryo development, and gives birth to the young one.
Q3. Explain the life cycle of a frog through metamorphosis.
Answer: The life cycle of a frog includes three main stages:
- Egg Stage: The female frog lays hundreds of eggs in water, where they are fertilised by sperms released by the male (external fertilisation).
- Tadpole (Larva) Stage: Eggs hatch into tadpoles, which have a tail, gills for breathing in water, and feed on plants.
- Adult Frog: Gradually, the tail disappears, gills are replaced by lungs, and limbs develop. The tadpole transforms into an adult frog that can live both on land and in water.
This complete change from tadpole to frog is called metamorphosis.
Q4. Explain the development of a human baby from zygote to foetus.
Answer: When a sperm fuses with an ovum, a single cell called the zygote is formed. The zygote begins to divide rapidly to form a ball of cells known as the embryo. The embryo travels down the oviduct and gets attached to the wall of the uterus — this process is called implantation. Inside the uterus, the embryo gradually develops various body parts such as head, eyes, hands, legs, and internal organs. After about eight weeks, when most body parts can be identified, the embryo is called a foetus. The foetus continues to grow inside the mother’s uterus for about nine months before the baby is born.
Q5. What is cloning? Describe the cloning of Dolly the sheep.
Answer: Cloning is the process of producing an exact genetic copy of a cell, tissue, or whole organism using artificial methods. Dolly the sheep was the first mammal to be successfully cloned. She was born on 5th July 1996 at the Roslin Institute, Scotland, by scientist Ian Wilmut and his team. The procedure involved:
- A cell was taken from the udder (mammary gland) of a female sheep (donor).
- An egg cell was taken from another sheep, and its nucleus was removed.
- The nucleus of the udder cell was inserted into the empty egg cell.
- The new egg developed into an embryo and was implanted in a surrogate mother sheep.
- After the gestation period, Dolly was born — a clone genetically identical to the donor sheep.
Dolly lived for about six and a half years and proved that adult body cells could be used to create a clone.
Additional Multiple Choice Questions (MCQ)
Q1. The male reproductive organ that produces sperms is the —
(a) Penis (b) Testes (c) Ovary (d) Uterus
Answer: (b) Testes
Q2. The female gamete is called —
(a) Sperm (b) Zygote (c) Ovum (d) Embryo
Answer: (c) Ovum
Q3. Fertilisation in frogs takes place —
(a) Inside the female body (b) Outside the body in water (c) In the uterus (d) In the soil
Answer: (b) Outside the body in water
Q4. Which of the following animals reproduces by budding?
(a) Amoeba (b) Hydra (c) Frog (d) Hen
Answer: (b) Hydra
Q5. Binary fission is observed in —
(a) Hydra (b) Frog (c) Amoeba (d) Butterfly
Answer: (c) Amoeba
Q6. Dolly was a cloned —
(a) Cow (b) Sheep (c) Dog (d) Goat
Answer: (b) Sheep
Q7. The fusion of male and female gametes is called —
(a) Cloning (b) Budding (c) Fertilisation (d) Metamorphosis
Answer: (c) Fertilisation
Q8. Animals that lay eggs are called —
(a) Viviparous (b) Oviparous (c) Mammals (d) Carnivorous
Answer: (b) Oviparous
Q9. The young one of a frog is called —
(a) Caterpillar (b) Tadpole (c) Larva (d) Pupa
Answer: (b) Tadpole
Q10. The fertilised egg is called —
(a) Embryo (b) Zygote (c) Foetus (d) Bud
Answer: (b) Zygote
Fill in the Blanks
Q1. The male gamete is called __________.
Answer: sperm
Q2. The female reproductive organ that produces ova is the __________.
Answer: ovary
Q3. The transformation of a tadpole into a frog is called __________.
Answer: metamorphosis
Q4. Hydra reproduces asexually by __________.
Answer: budding
Q5. The first cloned mammal was __________.
Answer: Dolly the sheep
True or False
Q1. Sperms are produced in the ovary.
Answer: False (Sperms are produced in the testes.)
Q2. Internal fertilisation occurs in humans.
Answer: True
Q3. Amoeba reproduces by budding.
Answer: False (Amoeba reproduces by binary fission.)
Q4. A hen is a viviparous animal.
Answer: False (A hen is an oviparous animal because it lays eggs.)
Q5. The zygote develops into the embryo.
Answer: True
Glossary
| Term | Meaning |
|---|---|
| Reproduction | The biological process of producing new individuals of the same species. |
| Sexual Reproduction | Reproduction involving two parents and the fusion of gametes. |
| Asexual Reproduction | Reproduction involving only one parent without the fusion of gametes. |
| Gamete | A reproductive cell — sperm in males and ovum in females. |
| Sperm | The male gamete produced by the testes. |
| Ovum | The female gamete produced by the ovary. |
| Testes | Male reproductive organs that produce sperms. |
| Ovary | Female reproductive organ that produces ova. |
| Oviduct | The tube that carries the ovum from the ovary to the uterus. |
| Uterus | The muscular organ where the embryo develops into a baby. |
| Fertilisation | Fusion of sperm and ovum to form a zygote. |
| Internal Fertilisation | Fertilisation that takes place inside the female body. |
| External Fertilisation | Fertilisation that takes place outside the female body, usually in water. |
| Zygote | The single cell formed after fertilisation. |
| Embryo | The early stage of development of a new individual after fertilisation. |
| Foetus | An advanced stage of embryo where body parts are clearly identifiable. |
| Viviparous Animals | Animals that give birth to young ones (e.g., humans, cows). |
| Oviparous Animals | Animals that lay eggs (e.g., hens, frogs). |
| Metamorphosis | The transformation of a larva into an adult through drastic changes. |
| Tadpole | The larval stage of a frog. |
| Budding | Asexual reproduction where a new individual grows as a bud on the parent. |
| Binary Fission | Asexual reproduction where the parent cell splits into two equal daughter cells. |
| Hydra | A simple aquatic animal that reproduces by budding. |
| Amoeba | A unicellular organism that reproduces by binary fission. |
| Cloning | Producing an exact genetic copy of an organism by artificial means. |
| Dolly | The first mammal (sheep) cloned successfully in 1996. |