Level: Class 8, Science, by Dr E. Ramanathan PhD
Mindmap
Prepare flashcards based on the mindmap shown here
Study Notes
The Genesis of Species: Biological Modes of Reproduction
- Overview: Provides a comprehensive overview of animal reproduction, covering both sexual and asexual modes.
- Sexual Reproduction
- Begins with the fusion of male and female reproductive cells (gametes).
- Reproductive Organs:
- Male (Humans): Testes (produce sperms), sperm ducts, and a penis.
- Female (Humans): Ovaries (produce ova/eggs), oviducts, and a uterus.
- Both sperms and eggs are single cells.
- Fertilisation: The fusion of an egg and a sperm, resulting in a single-celled zygote.
- Internal: Occurs inside the female’s body (e.g., humans, cows, hens).
- External: Occurs outside the body in water environments (e.g., frogs, fish).
- Embryo Development:
- The zygote divides repeatedly to form a ball of cells called an embryo, which embeds into the uterus wall.
- Once the embryo develops identifiable body parts, it is called a foetus.
- Oviparous vs. Viviparous:
- Viviparous: Animals that give birth to live young (e.g., humans, dogs).
- Oviparous: Animals that lay eggs (e.g., frogs, hens, butterflies).
- Metamorphosis: Drastic biological changes from larvae (tadpoles) into adults (e.g., frogs).
- Asexual Reproduction
- Requires only a single parent.
- Budding: New individuals develop from outgrowths or “buds” on the parent’s body (e.g., hydra).
- Binary Fission: Microscopic, single-celled organisms (e.g., amoebas) reproduce by dividing their nucleus and body into two separate, identical individuals.
- Cloning
- The production of an exact genetic copy of a cell or complete organism.
- Dolly the sheep (1996) was the first mammal successfully cloned by scientists in Scotland.
FAQ
What is the purpose of the tail in a sperm?
Why do frogs lay hundreds of eggs instead of one?
How does IVF or in vitro fertilisation actually work?
Target Practice
Instructions
- Answer all 10 questions.
- Each question carries 3 marks.
- Write brief and clear answers.
- Click Submit & Show All Keys after completion.
Q1. What is sexual reproduction? Name the male and female reproductive cells involved in it.
3 Marks
Key: Sexual reproduction is the mode of reproduction in which male and female gametes fuse. The male reproductive cell is the sperm and the female reproductive cell is the ovum or egg.
Q2. Name the main reproductive organs in human males and females.
3 Marks
Key: In human males, the main reproductive organs are testes, sperm ducts and penis. In human females, the main reproductive organs are ovaries, oviducts and uterus.
Q3. What is fertilisation? Differentiate between internal and external fertilisation with one example each.
3 Marks
Key: Fertilisation is the fusion of a sperm and an egg to form a zygote. Internal fertilisation occurs inside the female body, for example in humans. External fertilisation occurs outside the body, usually in water, for example in frogs or fish.
Q4. What is a zygote? How does it develop into an embryo and then a foetus?
3 Marks
Key: A zygote is the single cell formed after fertilisation. It divides repeatedly to form a ball of cells called an embryo. As development continues and body parts become identifiable, it is called a foetus.
Q5. Distinguish between oviparous and viviparous animals with two examples each.
3 Marks
Key: Oviparous animals lay eggs, for example hen and frog. Viviparous animals give birth to young ones, for example humans and dogs.
Q6. What is metamorphosis? Explain it with reference to the life cycle of a frog.
3 Marks
Key: Metamorphosis is the drastic change in body form during development from larva to adult. In frogs, eggs hatch into tadpoles, which have tails and gills. They gradually develop legs, lungs and adult frog features.
Q7. What is asexual reproduction? Why is only one parent needed in this method?
3 Marks
Key: Asexual reproduction is the mode of reproduction in which a new individual is produced from a single parent without fusion of gametes. Only one parent is needed because there is no fertilisation involved.
Q8. Explain budding in hydra.
3 Marks
Key: In hydra, a small outgrowth called a bud develops on the parent body due to repeated cell division. The bud grows, develops tentacles and finally detaches to become a new hydra.
Q9. Describe binary fission in amoeba.
3 Marks
Key: Binary fission is a type of asexual reproduction seen in amoeba. First the nucleus divides into two. Then the body splits into two identical daughter amoebae, each with one nucleus.
Q10. What is cloning? Who was Dolly and why is she important in biology?
3 Marks
Key: Cloning is the production of an exact genetic copy of a cell or organism. Dolly was the first mammal successfully cloned by scientists in Scotland in 1996. She proved that cloning of mammals was possible.
Total Questions
10
Marks per Question
3
Total Marks
30
Status
Not Submitted
NOTE:
- Enter the questions in your Question Bank.
- Practice the answer in your Guided practice notebook.
- Submit. Evaluate yourself or and handover to the mentor and get it corrected.
- Share the score to your mentor in telegram.
- Complete the missed out or wrong answers.
- Finish the target test answers in your Target Practice Note book.
