ICSE – Grade 9 – Biology – Ch 05 – QA

1. Define pollination. Describe the types of pollination with examples.
    Answer:
    Pollination is the transfer of pollen grains from the anther to the stigma of a flower. It is of two types:

• Self-Pollination: Transfer of pollen grains occurs within the same flower or between flowers of the same plant. Example: Pea, Wheat.
• Cross-Pollination: Pollen grains are transferred from one plant to another plant of the same species. Example: Papaya, Apple.

2. Compare and contrast self-pollination and cross-pollination.
   Answer:

• Self-Pollination:
  
  
  
  • Occurs within the same plant.
  • No external agents required.
  • Less variation in offspring.
  • Example: Rice, Wheat.
• Cross-Pollination:
  
  
  
  • Occurs between two plants of the same species.
  • Requires external agents.
  • Leads to genetic variation.
  • Example: Papaya, Maize.

3. Explain the advantages and disadvantages of self-pollination.
   Answer:

• Advantages:
  • No need for pollinating agents.
  • Parental traits preserved.
  • Less pollen wastage.
• Disadvantages:
  • Offspring may be weaker.
  • No new varieties or genetic diversity.

4. Explain the advantages and disadvantages of cross-pollination.
   Answer:

• Advantages:
  • Offspring are vigorous and healthy.
  • Promotes variation and evolution.
• Disadvantages:
  • Requires external agents.
  • More pollen is wasted.

5. List and describe the agents of pollination with examples.
   Answer:

• Wind (Anemophily): Light, dry pollen; feathery stigma. Example: Maize.
• Insects (Entomophily): Bright petals, nectar. Example: Rose.
• Water (Hydrophily): Floating pollen. Example: Vallisneria.
• Animals (Zoophily): Birds or bats. Example: Banana.

6. Describe the adaptations in flowers for wind pollination.
   Answer:

• Pollen grains are light and dry.
• Anthers are long and hang outside the flower.
• Stigmas are large and feathery.
• Example: Maize.

7. Describe the adaptations in flowers for insect pollination.
   Answer:

• Brightly coloured petals.
• Presence of nectar and scent.
• Sticky or spiny pollen for adhesion.
• Example: Hibiscus.

8. Explain the process of fertilization in flowering plants.
   Answer:

• After pollination, pollen grain germinates on the stigma.
• Forms a pollen tube through the style to the ovule.
• Two male gametes enter the embryo sac.
• One fuses with egg → Zygote.
• Other fuses with polar nuclei → Endosperm.
• This is called Double Fertilization.

9. What is double fertilization? Why is it important?
   Answer:
   Double fertilization is the fusion of one male gamete with the egg (zygote formation) and the other with two polar nuclei (endosperm formation).

• It ensures formation of both embryo and food source.
• Found only in angiosperms.

10. Describe post-fertilization changes in a flower.
    Answer:

• Zygote → Embryo
• Ovule → Seed
• Ovary → Fruit
• Integuments → Seed coat
• Endosperm nucleus → Endosperm (nutrition)

11. What is unisexuality? How does it promote cross-pollination? Give examples.
    Answer:
    Unisexuality (also called dicliny) means that male and female flowers are present on different parts of the same plant (monoecious) or on different plants (dioecious).

• This prevents self-pollination.
• It promotes cross-pollination since pollen must travel to another flower.
• Example: Papaya (dioecious), Maize (monoecious).

12. What is herkogamy? How does it ensure cross-pollination?
    Answer:
    Herkogamy is the presence of a natural physical barrier between anthers and stigmas in bisexual flowers.

• Prevents self-pollination even though both sex organs are present.
• Encourages cross-pollination.
• Example: Petunia.

13. Define dichogamy. Mention its types with examples.
    Answer:
    Dichogamy is the maturation of anther and stigma at different times.

• Prevents self-pollination.
   Types:
• Protandry: Anthers mature first. Example: Sunflower.
• Protogyny: Stigmas mature first. Example: Avocado.

14. What is self-sterility? How does it help in cross-pollination?
    Answer:
    Self-sterility is the condition where a flower’s own pollen cannot fertilize its ovule.

• Pollen fails to germinate on the stigma of the same flower.
• Promotes cross-pollination.
• Example: Potato.

15. Explain the structure and germination of a pollen grain.
    Answer:

• Pollen grains are produced in the anther.
• They have a tough outer wall (exine) and a thin inner wall (intine).
• When it lands on a compatible stigma, it germinates by forming a pollen tube.
• This tube grows down the style into the ovule for fertilization.

16. Describe the structure and function of the embryo sac.
    Answer:
    The embryo sac is the female gametophyte inside the ovule.

• It has seven cells and eight nuclei:
  • One egg cell
  • Two synergids
  • Three antipodal cells
  • One central cell with two polar nuclei
• Function: Site of fertilization and development of the zygote and endosperm.

17. What are the characteristics of wind-pollinated flowers?
    Answer:

• Small, inconspicuous flowers.
• No scent or nectar.
• Light, dry, and powdery pollen.
• Long anthers and feathery stigma.
• Example: Maize.

18. What are the characteristics of insect-pollinated flowers?
    Answer:

• Bright, large petals.
• Sweet scent and nectar.
• Sticky or spiny pollen.
• Stigma often sticky for better pollen adhesion.
• Example: Rose, Hibiscus.

19. Discuss the significance of pollination in plants.
    Answer:

• Enables fertilization and seed formation.
• Ensures transfer of male gametes.
• Promotes genetic variation (especially cross-pollination).
• Vital for reproduction and evolution of plant species.

20. What is the role of endosperm in the seed?
    Answer:

• Formed by the fusion of one male gamete with two polar nuclei (triple fusion).
• Serves as a food source for the developing embryo.
• Contains stored nutrients like starch, proteins, and oils.

21. What is double fertilization? Describe the process in detail.
    Answer:
    Double fertilization occurs in flowering plants and involves two fusion events:

1. A pollen grain lands on the stigma and germinates, forming a pollen tube.
2. The pollen tube carries two male gametes to the ovule.
3. One male gamete fuses with the egg cell → forms a diploid zygote.
4. The other male gamete fuses with two polar nuclei in the embryo sac → forms triploid endosperm nucleus.
    This process is unique to angiosperms and is called double fertilization.

22. What changes occur in a flower after fertilization?
    Answer:
    After fertilization:

• Zygote → Embryo
• Ovule → Seed
• Ovary → Fruit
• Integuments → Seed coat
• Endosperm nucleus → Endosperm
   These changes help protect and nourish the developing embryo and ensure seed dispersal.

23. Differentiate between self-pollination and cross-pollination.
    Answer:
    Self-Pollination:

• Pollen from anther lands on stigma of same flower or same plant.
• No external agent needed.
• Less genetic variation.
• Examples: Pea, Wheat.

Cross-Pollination:

• Pollen transferred to stigma of a different plant.
• Requires agents like wind or insects.
• Promotes genetic diversity.
• Examples: Papaya, Apple.

24. What are the adaptations in plants that promote cross-pollination?
    Answer:
    Adaptations for cross-pollination include:

1. Unisexuality (Dicliny): Separate male and female flowers (e.g., Papaya).
2. Herkogamy: Physical barrier between anther and stigma (e.g., Petunia).
3. Dichogamy: Anther and stigma mature at different times (e.g., Sunflower).
4. Self-Sterility: Pollen cannot fertilize same flower (e.g., Potato).

25. Describe the structure and role of a seed.
    Answer:
    A seed consists of:

• Seed coat: Protective outer covering from integuments.
• Embryo: Formed from zygote; develops into a new plant.
• Endosperm: Triploid tissue; stores nutrients.
   Role:
• Ensures species survival.
• Protects embryo.
• Allows dormancy and dispersal.

26. How is pollination by water (hydrophily) carried out? Give example.
    Answer:
    In hydrophily:

• Pollen grains are released into water.
• They float and reach the stigma of female flowers.
• Pollen grains are protected from water damage.
   Example: Vallisneria.

27. Write a short note on pollination by animals (zoophily).
    Answer:
    Some flowers are pollinated by birds, bats, and other animals.
     Features:

• Large, colorful, and scented flowers.
• Produce large amounts of nectar.
• Animals feed on nectar and carry pollen to other flowers.
   Example: Sunbird pollinates flowers like hibiscus.

28. Why is cross-pollination preferred over self-pollination in nature?
    Answer:
    Cross-pollination is preferred because:

• Produces healthier and more vigorous offspring.
• Increases genetic diversity.
• Leads to development of new varieties.
   Though it requires more energy and resources, it ensures evolutionary advantage.

29. Explain the advantages and disadvantages of self-pollination.
    Answer:
    Advantages:

• No need for external agents.
• Parental traits preserved.
• Less pollen wastage.

Disadvantages:

• Weaker offspring.
• No genetic variation.
• Cannot adapt well to changing environments.

30. Explain the role of the stigma in pollination.
    Answer:
    The stigma is the receptive part of the female reproductive organ.
     Role:

• Receives pollen grains.
• Secretes sticky substances to trap pollen.
• Supports pollen germination.
• Helps guide the pollen tube toward the ovule.

31. Describe the structure and role of the stigma in pollination.
    Answer:

• The stigma is the upper part of the pistil and is usually sticky or feathery.
• Its structure is adapted to trap and hold pollen grains.
• In wind-pollinated flowers, it is feathery and large to catch airborne pollen.
• In insect-pollinated flowers, it is sticky to catch pollen from insect bodies.
• It plays a vital role in ensuring pollen germination and successful fertilization.

32. Explain why flowers like papaya and maize depend on cross-pollination.
    Answer:

• Papaya is a unisexual plant – male and female flowers occur on different plants.
• Maize has male and female flowers on the same plant but spatially separated.
• This arrangement prevents self-pollination.
• These flowers require external agents (wind or insects) to transfer pollen.
• Cross-pollination is necessary for these plants to set seeds and reproduce.

33. How is the ovary converted into a fruit after fertilization?
    Answer:

• After fertilization, the ovary undergoes several changes:
  • The ovule becomes the seed.
  • The zygote develops into an embryo.
  • The integuments form the seed coat.
  • The ovary wall enlarges and differentiates into fruit tissue.
• This transformation protects and nourishes the developing seed.
• The fruit also helps in seed dispersal.

34. What changes take place in the ovule after fertilization?
    Answer:

• The ovule transforms into the seed.
• The fertilized egg (zygote) develops into the embryo.
• The secondary nucleus fuses with a male gamete to form the endosperm nucleus → forms endosperm (food for embryo).
• The outer layers of the ovule become the seed coat.
• The seed becomes capable of giving rise to a new plant upon germination.

35. What is the role of the pollen tube in fertilization?
    Answer:

• The pollen tube forms from a germinating pollen grain on the stigma.
• It carries two male gametes.
• The tube grows through the style and reaches the ovule via the micropyle.
• It releases the gametes into the embryo sac.
• One gamete fuses with the egg (zygote), and the other with the polar nuclei (endosperm).
• This is essential for double fertilization.

36. Why is cross-pollination biologically more advantageous than self-pollination?
    Answer:

• Cross-pollination combines genetic material from two different plants.
• It introduces genetic variation among offspring.
• Increases adaptability and survival of species.
• Results in vigorous and healthy plants.
• Helps plants evolve better traits over generations.
   While it requires external agents, its evolutionary benefits outweigh the disadvantages.

37. What are the structural adaptations of wind-pollinated flowers?
    Answer:

• Pollen grains are light, dry, and powdery to travel easily in air.
• Anthers are long and hang outside the flower for better exposure.
• Stigmas are large and feathery to catch pollen.
• Flowers are usually small and not brightly coloured (no need to attract pollinators).
• They produce large quantities of pollen to ensure success.
   Example: Maize.

38. Why do plants ensure mechanisms to avoid self-pollination?
    Answer:

• Self-pollination results in no genetic variation.
• Leads to weak and less adaptable offspring.
• Repeated self-pollination can cause genetic diseases and inbreeding depression.
• To maintain diversity and survival of species, plants promote cross-pollination.
• Mechanisms like dichogamy, herkogamy, self-sterility, and unisexuality help prevent it.

39. Describe double fertilization in flowering plants.
    Answer:

• Unique to angiosperms (flowering plants).
• After the pollen tube enters the embryo sac:
  • One male gamete fuses with the egg → zygote (diploid).
  • The other male gamete fuses with the two polar nuclei → endosperm nucleus (triploid).
• This dual fusion is known as double fertilization.
• Zygote → embryo, Endosperm nucleus → endosperm (food storage).
• Ensures nourishment for developing embryo.

40. Write the post-fertilization changes in a flower in tabular form.
    Answer:

After fertilization:

• Zygote → Embryo
• Ovule → Seed
• Integuments → Seed coat
• Ovary → Fruit
• Endosperm nucleus → Endosperm

These changes prepare the flower for seed dispersal and the development of the next generation.