Question 1

(i) Self-pollination

(ii) Cross-pollination

(iii) Fertilisation

(iv) Tissue culture

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

Accepted Answer

1. The question seems incomplete but likely asks which process is ensured here. The four processes are given: (i) Self-pollination, (ii) Cross-pollination, (iii) Fertilisation, (iv) Tissue culture.

2. Correct order of stages of sexual reproduction in plants:

(iii) Pollination → (i) Pollen germination on stigma → (ii) Fertilisation → (iv) Formation of zygote.

Explanation:
- Pollination is the transfer of pollen grains to the stigma.
- Pollen grains germinate on the stigma.
- Fertilisation occurs when male gamete fuses with female gamete.
- Formation of zygote is the result of fertilisation. — Pollination is the first step where pollen grains reach the stigma. Then pollen germinates on the stigma producing pollen tube. Fertilisation occurs when male gamete reaches ovule and fuses with female gamete. This results in the formation of zygote.

Question 2

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.

(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.

Accepted Answer

A is false, but R is true.

Explanation: The zygote does not immediately attach to the uterus wall after fertilisation. It takes some time to develop into a blastocyst and then implants into the uterus wall. However, the uterus wall is prepared to receive the zygote during the menstrual cycle by thickening and developing blood vessels. — Fertilisation occurs in the fallopian tube. The zygote travels to the uterus and only after reaching the blastocyst stage does it implant in the uterus wall. Hence, assertion is false. The uterus wall is prepared by hormonal changes, so reason is true.

Question 3

Why does asexual reproduction produce offsprings that are genetically identical to the parent?

Accepted Answer

Asexual reproduction involves only one parent and does not involve the fusion of gametes. The offspring are produced by mitotic division of the parent cells, so they inherit the exact genetic material of the parent. Hence, the offspring are genetically identical clones of the parent. — Since there is no exchange or recombination of genetic material in asexual reproduction, the genetic makeup remains unchanged, producing identical offspring.

Question 4

Explain why the menstrual cycle stops during pregnancy.

Accepted Answer

During pregnancy, the fertilised egg implants in the uterus and produces hormones like human chorionic gonadotropin (hCG) which maintain the corpus luteum. The corpus luteum continues to secrete progesterone which prevents the shedding of the uterine lining. Hence, the menstrual cycle stops during pregnancy. — Progesterone maintains the uterine lining to support the developing embryo and prevents menstruation. This hormonal regulation stops the menstrual cycle until after childbirth.

Question 5

Why are flowers that bloom at night white or light in colour as compared to flowers that bloom during the day?

Accepted Answer

Flowers that bloom at night are usually white or light coloured to attract nocturnal pollinators like moths and bats. Light colours are more visible in low light conditions, helping pollinators locate the flowers easily at night. — Bright or white colours reflect moonlight or starlight, making the flowers stand out in darkness, thus aiding pollination by night-active animals.

Question 6

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

Accepted Answer

Vegetatively propagated plants are genetically identical clones of the parent plant, so if the parent has susceptibility to a disease, all offspring will have the same susceptibility. Sexual reproduction creates genetic variation which can lead to disease resistance in some offspring, making them less vulnerable overall. — Lack of genetic diversity in vegetative propagation means diseases can spread rapidly and affect all plants similarly.

Question 7

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.

Accepted Answer

If a plant species only undergoes self-pollination, genetic diversity would decrease over generations because self-pollination involves the fusion of gametes from the same plant, leading to homozygosity. This reduces variation and may increase the chances of harmful recessive traits appearing. — Cross-pollination introduces new gene combinations, increasing diversity. Without it, the gene pool shrinks, reducing adaptability.

Question 8

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

Accepted Answer

The farmer can use vegetative propagation methods such as cutting, grafting, layering, or tissue culture. These methods produce genetically identical plants (clones) quickly without the need for seeds. Tissue culture is especially effective for rapid multiplication under controlled conditions. — Vegetative propagation bypasses the seed stage and produces clones, ensuring uniformity and faster production of plants.

Question 9

Suresh prepares slides with pollen grains in different sugar concentrations (0%, 2.5%, 5%, 7.5%, 10%) to study the germination of pollen.

(i) What are the different hypotheses which can be tested using this set-up?

(ii) What parameters should be kept the same in this set-up?

Accepted Answer

(i) Hypotheses that can be tested:
- Pollen germination depends on sugar concentration.
- There is an optimum sugar concentration for maximum pollen germination.
- Higher or lower sugar concentrations affect the rate or extent of pollen germination.

(ii) Parameters to keep constant:
- Temperature
- pH of the solution
- Duration of incubation
- Source and freshness of pollen grains
- Volume of solution used
- Humidity conditions — By varying only sugar concentration and keeping other factors constant, the effect of sugar concentration on pollen germination can be accurately studied.

Question 10

Look at the picture given below and think in line with the given prompts and find out which type(s) of pollination might have been followed in these flowers —

Tomato: Stamens cover the stigma.

Wheat: Flowers open after pollination.

Papaya: Male and female flowers are often borne on different papaya trees.

Accepted Answer

Tomato: Since stamens cover the stigma, self-pollination is likely.

Wheat: Flowers open after pollination, indicating cleistogamy or self-pollination before flower opening.

Papaya: Male and female flowers on different trees indicate cross-pollination (dioecious plants).

Explanation:
- Tomato flowers usually self-pollinate as stamens enclose stigma.
- Wheat flowers are mostly self-pollinated.
- Papaya requires cross-pollination between male and female trees. — The flower structure and arrangement indicate the mode of pollination. Stamens covering stigma favor self-pollination; separate male and female flowers require cross-pollination.

Question 11

In the lower Himalayan region of northern India, apples are an important cash crop that contribute significantly to farmer's livelihoods. The fruit yield in apple cultivation is declining continuously, associated with climate change and a significant decline in the population of natural pollinators. A researcher-farmer group set up two experimental apple orchards at two distinct locations: Places A and B. In apple orchards at Place A, they allowed natural pollinators to pollinate the flowers of the apple. In apple orchards at Place B, they applied mixed farming techniques of beekeeping. Along with honey, the farmer yielded apples. The yield of apples is depicted in Fig. 11.24, in terms of fruit setting (number of fruits/the total number of corresponding fruit-bearing branches) and fruit drop (premature falling of developing fruits) in the two types of experimental places of apple orchards.

(i) What are the hypotheses the researcher-farmers group has thought of for this investigation?

(ii) What are the different parameters in the experiment?

(iii) Compare and analyse the data of two experimental orchards Places A and B, in terms of high yields of apple fruits.

(iv) Based on your analysis, what do you infer from the data?

Accepted Answer

(i) Hypotheses:
- The presence of natural pollinators affects apple fruit yield.
- Beekeeping (managed pollinators) increases apple fruit yield and reduces fruit drop.

(ii) Parameters:
- Fruit setting (number of fruits per fruit-bearing branch)
- Fruit drop (premature falling of fruits)
- Presence or absence of managed pollinators (bees)

(iii) Analysis:
- Place B with beekeeping shows higher fruit setting and lower fruit drop compared to Place A.
- Managed pollinators improve pollination efficiency leading to better fruit yield.

(iv) Inference:
- Beekeeping enhances pollination and fruit yield in apple orchards.
- Decline in natural pollinators negatively impacts fruit production.
- Mixed farming with beekeeping is beneficial for apple cultivation. — The experiment compares natural pollination with managed pollination (beekeeping). Data shows managed pollination improves fruit set and reduces fruit drop, indicating better yield.

Question 12

A student claims, "In humans, ovulation always happens on day 14 of the menstrual cycle". Critically examine this claim and state whether the claim is correct or not. Give at least two reasons for your answer.

Accepted Answer

The claim is not always correct. Ovulation generally occurs around day 14 in a 28-day menstrual cycle, but the exact day can vary among individuals and cycles. Reasons:
1. The length of menstrual cycles varies from woman to woman and even from cycle to cycle.
2. Factors like stress, illness, and hormonal imbalances can shift the timing of ovulation.
Therefore, ovulation does not always happen exactly on day 14. — Menstrual cycles are not fixed at 28 days for all women; ovulation timing depends on cycle length and physiological conditions.

Question 13

(i) Self-pollination

(ii) Cross-pollination

(iii) Fertilisation

(iv) Tissue culture

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

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.

(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.

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

5. Explain why the menstrual cycle stops during pregnancy.

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

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

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.

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

Accepted Answer

1. The question seems incomplete but likely asks to identify which method ensures genetic identity or reproduction.

2. Correct order of stages of sexual reproduction in plants:
 (iii) Pollination → (i) Pollen germination on stigma → (ii) Fertilisation → (iv) Formation of zygote.

3. Assertion and Reason:
 - Assertion (A) is false because the zygote does not immediately attach to the uterus wall; it first undergoes several divisions forming a blastocyst.
 - Reason (R) is true because the uterus wall is prepared (through hormonal changes) to receive the zygote.
 - Correct option: (iv) A is false, but R is true.

4. Asexual reproduction produces genetically identical offspring because it involves only one parent and no fusion of gametes, so the offspring inherit the exact genetic material of the parent.

5. Menstrual cycle stops during pregnancy because hormonal changes (increased progesterone and estrogen) maintain the uterine lining and prevent ovulation.

6. Flowers that bloom at night are white or light-colored to attract nocturnal pollinators like moths and bats, which are attracted to pale colors in low light.

7. Vegetatively propagated plants are more vulnerable to diseases because they are genetically identical clones, so a disease affecting one can affect all.

8. If all flowers are only capable of self-pollination, genetic diversity will decrease over generations, making plants more susceptible to diseases and environmental changes.

9. Suitable methods include tissue culture and vegetative propagation because they produce genetically identical plants quickly and in large numbers. — Stepwise explanation provided above for each question part.

- For ordering stages, understanding the sequence of pollination, germination, fertilisation, and zygote formation is essential.
- For assertion-reason, knowledge of early embryonic development and uterine preparation is needed.
- Genetic identity in asexual reproduction is due to absence of gamete fusion.
- Menstrual cycle halts due to hormonal regulation during pregnancy.
- Flower color adaptation relates to pollinator behavior.
- Vulnerability in vegetative propagation arises from lack of genetic variation.
- Self-pollination reduces genetic diversity.
- Tissue culture and vegetative propagation are efficient for cloning plants.

Question 14

Suresh prepares slides with pollen grains in different sugar concentrations (0%, 2.5%, 5%, 7.5%, 10%) to study the germination of pollen.

(i) What are the different hypotheses which can be tested using this set-up?

(ii) What parameters should be kept the same in this set-up?

Accepted Answer

(i) Hypotheses that can be tested:
- The effect of sugar concentration on pollen germination rate.
- Whether pollen grains require a certain sugar concentration for optimal germination.
- The relationship between osmotic concentration and pollen tube growth.

(ii) Parameters to keep the same:
- Temperature of the environment.
- Type and source of pollen grains.
- Duration of incubation.
- Volume of the sugar solution.
- pH of the sugar solutions.
- Light conditions during the experiment. — To test the effect of sugar concentration on pollen germination, all other factors must be controlled to ensure that any differences observed are due to sugar concentration alone. This includes keeping temperature, pollen type, incubation time, and other environmental factors constant.

Question 15

Look at the picture given below and think in line with the given prompts and find out which type(s) of pollination might have been followed in these flowers —

Tomato: Stamens cover the stigma.

Wheat: Flowers open after pollination.

Papaya: Male and female flowers are often borne on different papaya trees.

Accepted Answer

Tomato: Since stamens cover the stigma, self-pollination is likely predominant.

Wheat: Flowers open after pollination, indicating cleistogamy or self-pollination before flower opening.

Papaya: Male and female flowers on different trees indicate cross-pollination (dioecious plant). — Tomato flowers have stamens covering the stigma, facilitating self-pollination.
Wheat flowers opening after pollination suggests self-pollination occurs within closed flowers.
Papaya being dioecious requires cross-pollination between male and female trees.

Reproduction: How Life Continues

Reproduction: How Life Continues — Study Notes

11.1 Asexual Reproduction

Asexual Reproduction in Other Organisms

11.2 Sexual Reproduction

Practice Questions — Reproduction: How Life Continues

Reproduction: How Life Continues — Study Guides & Articles

All 13 Chapters in Science