Sexual Reproduction — Phases
Chapter: Reproduction in Organisms | Topic: Sexual Reproduction Phases
SEXUAL REPRODUCTION — PHASES
Topic: Sexual Reproduction Phases
Multiple Choice Questions
Q1. The three phases of sexual reproduction in organisms are:
- Birth, growth, and death
- Pre-fertilisation, fertilisation, and post-fertilisation events
- Mitosis, meiosis, and cytokinesis only
- Germination, flowering, and fruiting
Q2. Pre-fertilisation events include all the processes that occur:
- After the zygote is formed
- Before the fusion of male and female gametes
- During embryo development
- After seed formation
Q3. The formation of gametes through meiotic division is called:
- Fertilisation
- Gametogenesis
- Embryogenesis
- Parthenogenesis
Q4. In most sexually reproducing organisms, the male gamete is:
- Always larger and non-motile
- Usually smaller, motile, and produced in large numbers
- Always the same size as the female gamete
- Non-motile and produced in small numbers
Q5. The post-fertilisation phase in flowering plants involves:
- Only the formation of the zygote
- Events occurring after zygote formation, including embryogenesis and development of endosperm and seed
- Pollination and gamete transfer
- Formation of gametes only
Short Answer Questions
Q6. List the three main phases of sexual reproduction. Briefly state what happens in each phase.
Q7. Why are male gametes generally produced in much larger numbers than female gametes in most sexually reproducing organisms? Explain the biological significance.
Q8. Differentiate between isogametes and heterogametes. Give one example of an organism that produces each type.
Q9. In flowering plants, why is the post-fertilisation phase particularly complex compared to animals? Mention two unique events that occur in plants but not in animals during this phase.
Long Answer Questions
Q10. Describe the three phases of sexual reproduction in detail. Explain pre-fertilisation events (gametogenesis and gamete transfer), fertilisation (syngamy and development of the zygote), and post-fertilisation events (embryogenesis in animals, and embryogenesis, endosperm formation, and seed development in plants). Why is sexual reproduction considered more complex but evolutionarily advantageous than asexual reproduction?
Q11. "The events before fertilisation are all about preparation and chance; the events after fertilisation are all about precision and development." Analyse this statement by comparing the relative importance of: genetic variation generated during pre-fertilisation (meiosis), the randomness of fertilisation, and the highly regulated, programmed nature of embryonic development in post-fertilisation.
APPLICATION / ANALYSIS
Q12. Case Study — Reproductive Strategy Analysis:
A biologist studied four organisms:
| Organism | Gamete type | Fertilisation mode | Post-fertilisation development |
|---|---|---|---|
| Alga A | Isogametes | External in water | No embryo, zygote develops directly |
| Fish B | Heterogametes (small sperm, large egg) | External in water | Zygote develops outside, no parental care |
| Frog C | Heterogametes | External in water | Zygote develops into tadpole in water |
| Mammal D | Heterogametes | Internal | Zygote develops inside mother, extensive parental care |
Answer the following:
(a) Why does Alga A have isogametes while the others have heterogametes? What evolutionary trend does this show?
(b) Compare the chances of successful fertilisation in Fish B and Mammal D. Why does Mammal D invest so much more in fewer offspring?
(c) If pollution makes the water acidic in the frog's pond, which phase of sexual reproduction would be most affected, and why?
Q13. Real-Life Application — Assisted Reproductive Technology:
A couple in Delhi has been unable to conceive naturally. Their doctor explains the process of in vitro fertilisation (IVF):
Step 1: Hormonal stimulation to produce multiple eggs
Step 2: Egg retrieval from the woman's ovary
Step 3: Sperm collection and preparation
Step 4: Fertilisation in a laboratory dish
Step 5: Embryo culture for 3-5 days
Step 6: Embryo transfer to the uterus
Step 7: Pregnancy test after two weeks
Answer the following:
(a) Which natural phase of sexual reproduction does each IVF step correspond to? Map the steps to pre-fertilisation, fertilisation, and post-fertilisation events.
(b) Why are multiple eggs retrieved rather than just one? How does this relate to the natural process where many male gametes are produced but only one fertilises the egg?
(c) The doctor mentions that embryos can be frozen for future use. Which post-fertilisation event is being paused, and what cellular property allows this?