Class 9 - Chapter 11: Reproduction: How Life Continues

Exercise Solution

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?

Answer: (ii) Cross-pollination

Since pollen is transferred from a different plant of the same species to the stigma, cross-pollination is ensured.

2. Arrange the stages of sexual reproduction in plants in the correct order.

(i) Pollen germination on stigma

(ii) Fertilisation

(iii) Pollination

(iv) Formation of zygote

Correct Order:

Pollination → Pollen germination on stigma → Fertilisation → Formation of zygote

Answer: (iii) → (i) → (ii) → (iv)

3. Assertion–Reason

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.

The zygote does not immediately attach to the uterus wall. It first undergoes several cell divisions and forms an embryo before implantation.

Also, the uterus wall is not always prepared; it thickens during specific stages of the menstrual cycle.

Answer: (iv) A is false, but R is false.

4. Why does asexual reproduction produce offspring that are genetically identical to the parent?

Asexual reproduction involves only one parent and occurs through mitotic cell division. No fusion of gametes takes place, so the offspring receive the same genetic material as the parent. Therefore, the offspring are genetically identical and are called clones.

5. Explain why the menstrual cycle stops during pregnancy.

During pregnancy, the fertilised egg implants in the uterus and hormones such as progesterone maintain the uterine lining. Since the lining is required for the growth and nourishment of the developing embryo, it is not shed. Therefore, menstruation stops during pregnancy.

6. Why are flowers that bloom at night white or light-coloured as compared to flowers that bloom during the day?

Night-blooming flowers are usually white or light-coloured because these colours are more visible in dim light. They attract pollinators such as moths and other nocturnal insects more effectively during the night.

7. Why do vegetatively propagated plants tend to be more vulnerable to diseases than sexually reproduced plants?

Vegetative propagation produces genetically identical offspring. Since all plants have nearly the same genetic makeup, a disease affecting one plant can easily affect all others. Sexual reproduction introduces genetic variation, which increases disease resistance in the population.

8. If all flowers in a type of plant were only capable of self-pollination, how would it affect genetic diversity over several generations?

Self-pollination continuously uses genetic material from the same plant. As a result, very little genetic variation is produced. Over many generations, genetic diversity would decrease, making the species less adaptable to environmental changes and diseases.

9. A farmer wants to produce a large number of genetically identical plants quickly. Suggest suitable reproduction methods and explain why they are effective.

The farmer should use vegetative propagation methods such as:

• Cutting
• Layering
• Grafting
• Tissue culture

These methods produce large numbers of genetically identical plants in a short time. Tissue culture is especially useful because thousands of plants can be produced rapidly under controlled conditions.

10. Pollen Germination Experiment

(i) What hypotheses can be tested?

• Sugar solution is necessary for pollen germination.
• Different sugar concentrations affect pollen germination differently.
• There is an optimum sugar concentration for maximum pollen germination.

(ii) What parameters should be kept the same?

• Type of pollen grains
• Temperature
• Amount of solution
• Slide size
• Duration of observation
• Light conditions

11. Types of Pollination in the Given Flowers

(i) Tomato

The stamens cover the stigma, making self-pollination highly likely.

Answer: Self-pollination

(ii) Wheat

The flowers open only after pollination has already occurred.

Answer: Self-pollination

(iii) Papaya

Male and female flowers are often borne on different plants.

Answer: Cross-pollination

12. Apple Orchard Experiment

(i) What hypotheses are being investigated?

• Bee colonies increase pollination efficiency.
• Better pollination increases fruit set.
• Bee pollination reduces fruit drop.
• Bee pollination improves apple yield.

(ii) What are the parameters in the experiment?

Independent Variable: Presence of managed bee colonies.

Dependent Variables:

• Fruit set (%)
• Fruit drop (%)

Controlled Variables:

• Apple variety
• Climate conditions
• Orchard management practices
• Fertiliser and irrigation

(iii) Compare and analyse the data.

From the graph:

• Natural pollination gives about 26% fruit set.
• Bee colony pollination gives about 40% fruit set.
• Natural pollination results in about 35% fruit drop.
• Bee colony pollination reduces fruit drop to about 8%.

Therefore, orchards with bee colonies show higher fruit set and lower fruit drop.

(iv) What inference can be drawn?

Managed bee colonies significantly improve pollination, increase fruit production and reduce fruit loss. Beekeeping is therefore beneficial for apple cultivation.

13. A student claims that ovulation always happens on day 14 of the menstrual cycle. Critically examine the claim.

The claim is not completely correct.

Reason 1: Not all women have a 28-day menstrual cycle. Cycle length may vary from person to person.

Reason 2: Stress, illness, age, hormonal changes and lifestyle factors can shift the day of ovulation.

Ovulation generally occurs about 14 days before the next menstrual period, but it does not always occur exactly on the 14th day.

Hence The statement is incorrect because ovulation timing varies among individuals and across cycles.