NCERT Class 9 Science Chapter 11 Solutions – How Do Organisms Reproduce?
Looking for accurate and complete ncert class 9 science chapter 11 solutions for the new CBSE curriculum (2026-27)? You are in the right place! In this guide, we provide step-by-step, direct, and easy-to-understand solutions for all exercise questions from NCERT Exploration Class 9 Science Chapter 11: How Do Organisms Reproduce?.
These answers are crafted specifically to help students write clean, exam-ready answers in their notebooks without extra confusion or lengthy fluff.
Question 1
A flower's anthers are removed before it matures. Later, pollen from another plant of the same species is dusted onto its stigma and seeds are produced. Which process has been ensured here?
(i) Self-pollination (ii) Cross-pollination
(iii) Fertilisation (iv) Tissue culture
Correct Option: (ii) Cross-pollination
Explanation: Removing anthers (emasculation) prevents self-pollination. Introducing pollen from a different plant ensures cross-pollination.
Question 2
Arrange the following stages of sexual reproduction in plants in the correct order:
(i) Pollen germination on stigma (ii) Fertilisation
(iii) Pollination (iv) Formation of zygote
Correct Chronological Order:
(iii) → (i) → (ii) → (iv)
- 1. Pollination (iii): Transfer of pollen grains from anther to stigma.
- 2. Pollen germination on stigma (i): Formation of pollen tube down the style.
- 3. Fertilisation (ii): Fusion of male gamete with the female egg cell.
- 4. Formation of zygote (iv): Resulting single-celled diploid zygote is formed.
Question 3
Assertion (A): The zygote formed after fertilisation immediately attaches to the uterus wall.
Reason (R): The uterus wall is always prepared to receive the zygote.
Choose the correct option:
(i) Both A and R are true, and R is the correct explanation of A.
(ii) Both A and R are true, but R is not the correct explanation of A.
(iii) A is true, but R is false.
(iv) A is false, but R is true.
Correct Option: (iv) A is false, but R is true.
Explanation: The zygote does not attach *immediately*; it travels down the oviduct undergoing cell division over 5–7 days to become a blastocyst before implantation (though the uterine lining thickens cyclically, implantation takes time).
Question 4
Why does asexual reproduction produce offspring that are genetically identical to the parent?
Asexual reproduction involves only a single parent through mitotic cell divisions. There is no fusion of gametes (no mixing of parental DNA), resulting in exact clones of the parent organism.
Question 5
Explain why the menstrual cycle stops during pregnancy.
During pregnancy, high levels of hormones like progesterone and estrogen are continuously produced by the corpus luteum and placenta. These hormones maintain the thick uterine lining to support the developing embryo and prevent the maturation and release of new eggs, stopping the menstrual cycle.
Question 6
Why are flowers that bloom at night white or light in colour as compared to flowers that bloom during the day?
Night-blooming flowers are typically white or light-coloured so they can reflect moonlight effectively, making them easily visible to nocturnal pollinators like moths, bats, and beetles in low-light conditions. They also often release strong fragrances.
Question 7
Why do vegetatively propagated plants tend to be more vulnerable to diseases than sexually reproduced plants?
Vegetatively propagated plants are genetic clones. If a pathogen or disease infects one plant, the entire population lacks genetic variation and is equally susceptible, potentially wiping out the entire crop.
Question 8
If all flowers in a type of plant were only capable of self-pollination, how would it affect the genetic diversity over several generations? Explain.
Continuous self-pollination leads to a severe loss of genetic diversity over generations (inbreeding depression). Offspring become genetically uniform, reducing adaptability to environmental changes, climate shifts, and diseases.
Question 9
A farmer wants to produce a large number of genetically identical plants quickly. Suggest suitable reproduction methods and explain why they are effective.
Recommended Method: Micropropagation (Tissue Culture) or vegetative propagation (cutting/layering).
Why it is effective: Tissue culture allows thousands of plantlets (somaclones) to be grown from a tiny plant tissue sample in a nutrient medium under sterile conditions in a very short span, ensuring identical desirable traits.
Question 10
Suresh prepares slides with pollen grains in different sugar concentrations ($0\%, 2.5\%, 5\%, 7.5\%, 10\%$) to study pollen germination. (i) What hypotheses can be tested? (ii) What parameters should be kept the same?
- (i) Hypotheses: Sugars present in the stigma stimulate pollen tube growth; pollen germination rate depends directly on optimum sugar concentration.
- (ii) Constant Parameters: Temperature, humidity, time duration, type and maturity of pollen grains, and volume of drop on each slide.
Question 11
Look at the picture given in the textbook and identify the type(s) of pollination in Tomato, Wheat, and Papaya.
| Plant | Flower Characteristics | Type of Pollination |
|---|---|---|
| Tomato | Stamens cover the stigma | Self-pollination |
| Wheat | Flowers open after pollination | Cleistogamy / Self-pollination |
| Papaya | Male and female flowers on separate trees | Cross-pollination (Unisexual flowers) |
Question 12
In the lower Himalayan region, apple yield is declining due to climate change and pollinator decline. Orchard A relies on natural pollination; Orchard B uses bee colonies (beekeeping). Analyze the graph (Fig. 11.24) comparing Fruit Set (%) and Fruit Drop (%).
- (i) Hypotheses: Introducing bee colonies increases successful pollination and fruit setting while reducing premature fruit drop.
- (ii) Parameters: Apple variety, orchard location/climate, soil nutrients, watering schedule, and pest management.
- (iii) Data Analysis: Orchard B (with Bee Colony) shows a much higher Fruit Set ($\approx 40\%$) compared to Orchard A ($\approx 26\%$), and a much lower Fruit Drop ($\approx 8\%$) compared to Orchard A ($\approx 35\%$).
- (iv) Conclusion: Artificial introduction of managed bee colonies significantly boosts agricultural yield by compensating for declining natural pollinators.
Question 13
A student claims, "In humans, ovulation always happens on day 14 of the menstrual cycle". Critically examine this claim and state whether it is correct or not. Give at least two reasons.
The claim is incorrect.
Reasons:
- Variable Cycle Length: While ovulation typically occurs about 14 days *before* the next expected period, total menstrual cycle lengths vary among women (ranging from 21 to 35 days).
- Hormonal Fluctuations: Stress, health, diet, and lifestyle factors can shift the timing of ovulation from cycle to cycle.
Frequently Asked Questions (FAQs)
Based on latest NCERT class 9 book.