Fertilisation - External and Internal - UNSOLVED PRACTICE SET
Chapter: Reproduction in Organisms | Topic: Fertilisation External and Internal
FERTILISATION - EXTERNAL AND INTERNAL - UNSOLVED PRACTICE SET
Topic: Fertilisation External and Internal
Multiple Choice Questions
Q1. Fertilisation is defined as:
- The release of gametes from the body
- The fusion of a male gamete (sperm) with a female gamete (ovum) to form a diploid zygote
- The division of the zygote into multiple cells
- The development of the embryo
Q2. External fertilisation is commonly observed in:
- Humans and dogs
- Most bony fish, amphibians like frogs, and algae
- Birds and reptiles
- Flowering plants
Q3. Internal fertilisation is advantageous over external fertilisation because:
- It requires less energy
- It protects the gametes and embryo from predators and environmental fluctuations, increasing the chances of survival
- It produces more gametes
- It occurs in water
Q4. During fertilisation in flowering plants, the pollen tube carries:
- The ovule to the pollen grain
- The two male gametes from the pollen grain to the embryo sac in the ovule
- Water to the stigma
- The style to the anther
Q5. The process of double fertilisation in flowering plants, discovered by S.G. Nawaschin, involves:
- Fusion of one sperm with the egg and another sperm with the polar nuclei to form the primary endosperm nucleus
- Fusion of two eggs with one sperm
- Fusion of two sperms with one egg
- Fusion of the pollen tube with the stigma
Short Answer Questions
Q6. Differentiate between external and internal fertilisation. Give two examples of organisms for each type and mention one advantage and one disadvantage of each.
Q7. Why do organisms practising external fertilisation need to release enormous numbers of gametes? How does this contrast with organisms practising internal fertilisation?
Q8. Describe the process of fertilisation in a flowering plant from pollen deposition on the stigma to the formation of the zygote. What is unique about fertilisation in angiosperms?
Q9. A frog lays 2,000 eggs in water, but only about 50 tadpoles survive to adulthood. A hen lays one egg per day, and most chicks hatch and survive. Explain this difference based on the type of fertilisation.
Long Answer Questions
Q10. Explain fertilisation in detail. Compare external fertilisation (in fish and amphibians) and internal fertilisation (in reptiles, birds, and mammals) in terms of: site of fertilisation, number of gametes produced, chances of successful fertilisation, parental care, and survival rate of offspring. Why did internal fertilisation evolve as the dominant mode in terrestrial organisms?
Q11. "Double fertilisation in flowering plants is one of evolution's most elegant solutions." Discuss this statement by explaining: the process of double fertilisation (syngamy and triple fusion), the fate of the zygote and the primary endosperm nucleus, why the endosperm is triploid (3n), and the biological significance of this unique mechanism for plant reproduction and seed development.
APPLICATION / ANALYSIS
Q12. Case Study — Fertilisation Success Rates:
A marine biologist studied two populations:
| Organism | Fertilisation type | Eggs released per female | Sperm released per male | Successful zygotes per female |
|---|---|---|---|---|
| Sea urchin | External | 1 million | Billions | ~10,000 |
| Rabbit | Internal | 8-10 ova per cycle | Millions in ejaculate | 6-8 embryos typically |
Answer the following:
(a) Calculate the fertilisation success rate (percentage) for the sea urchin. Why is it so low despite the enormous number of gametes?
(b) Compare the parental energy investment per offspring in the sea urchin versus the rabbit. How does this relate to the type of fertilisation and development?
(c) If ocean acidification reduces sea urchin sperm motility by 50%, how would this affect the already low fertilisation success rate? Explain your reasoning.
Q13. Real-Life Application — Plant Breeding Programme:
A plant breeder in Hyderabad is trying to create a new variety of rice by crossing two parent plants with desirable traits:
Parent A: Disease-resistant but low yield
Parent B: High yield but susceptible to disease
The breeder needs to ensure that:
- Only Parent B's pollen fertilises Parent A's ovules
- No self-pollination occurs
Available tools:
- Paper bags to cover flowers
- Fine brush for manual pollination
- Scissors to remove anthers
- Labels to mark crossed flowers
Answer the following:
(a) Describe the step-by-step procedure the breeder must follow to achieve controlled cross-pollination. Which part of the flower must be removed first, and why?
(b) Why is it important to cover the emasculated flower with a bag immediately after removing the anthers? What unwanted event is being prevented?
(c) After successful fertilisation, what genetic outcome in the F1 generation would indicate that the cross was successful in combining both desirable traits?