🌸 Chapter 1
Sexual Reproduction in Flowering Plants
(5Marks )
🌸 Chapter 1 – Sexual
Reproduction in Flowering Plants
🔹 25 Important 5-Marks
Questions with Answers
1. Describe the structure of a
typical flower and explain how it is adapted for reproduction.
Answer:
A typical flower has four whorls:
1.
Calyx
(Sepals): Protect
the flower in bud stage.
2.
Corolla
(Petals): Brightly
colored to attract pollinators.
3.
Androecium
(Stamens): Male
reproductive organ; each stamen has an anther and filament.
4.
Gynoecium
(Carpels/Pistil):
Female reproductive organ; consists of stigma, style, and ovary.
Adaptations
for reproduction:
- Attractive petals and nectar
for pollination.
- Sticky stigma for pollen
reception.
- Anther dehisces to release
pollen.
- Ovary protects ovules and forms
fruit after fertilization.
2. Describe the structure of an
anther and explain the process of microsporogenesis.
Answer:
Structure:
- Each anther is bilobed with two
microsporangia per lobe.
- Microsporangium has four
layers:
1.
Epidermis
2.
Endothecium
3.
Middle
layers
4.
Tapetum
(nourishes developing pollen)
Microsporogenesis:
- Each pollen mother cell (2n)
undergoes meiosis to produce a tetrad of four haploid
microspores.
- Each microspore matures into a pollen
grain (male gametophyte).
This ensures genetic variation and gamete production.
3. Explain the structure and
development of male gametophyte (pollen grain).
Answer:
Structure:
- Exine: Outer wall made of
sporopollenin, resistant to decay.
- Intine: Inner wall made of cellulose
and pectin.
- Contains two cells:
- Vegetative cell: Large, vacuolated.
- Generative cell: Small, dense cytoplasm;
divides to form two male gametes.
Development:
Microspore → mitosis → 2-celled pollen → pollen germinates → pollen tube → male
gametes released.
4. Describe the structure of ovule
and explain the process of megasporogenesis.
Answer:
Structure:
- Each ovule has funicle, nucellus,
integuments, micropyle, and chalaza.
- The megaspore mother cell
(MMC) lies within the nucellus.
Megasporogenesis:
- MMC undergoes meiosis
forming four haploid megaspores.
- Three degenerate; one becomes functional
megaspore.
- Functional megaspore develops
into the embryo sac (female gametophyte) by three mitotic divisions
→ 8 nuclei and 7 cells (Polygonum type).
5. Explain the development and
structure of the embryo sac.
Answer:
- Functional megaspore undergoes three
mitotic divisions → 8 nuclei.
- Arrangement:
- Micropylar end: 1 egg cell + 2 synergids.
- Chalazal end: 3 antipodals.
- Central cell: 2 polar nuclei.
Total: 7 cells, 8 nuclei.
Functions:
- Egg cell – fuses with male
gamete (zygote).
- Polar nuclei – fuse with male
gamete (endosperm).
- Synergids – guide pollen tube.
6. Differentiate between
self-pollination and cross-pollination. Mention adaptations for each.
Answer:
|
Feature |
Self-Pollination |
Cross-Pollination |
|
Definition |
Pollen transferred to stigma of same flower or plant |
Pollen transferred to flower of another plant |
|
Genetic Effect |
No variation |
Produces variation |
|
Agents |
None |
Wind, water, insects |
|
Adaptations |
Bisexual flowers, closed buds |
Bright colors, nectar, unisexual flowers |
Cross-pollination
improves genetic diversity and plant evolution.
7. What are the agents of
pollination? Explain with adaptations and examples.
Answer:
1.
Wind
(Anemophily):
o Small, light pollen; feathery
stigma.
o Example: Maize, rice.
2.
Water
(Hydrophily):
o Pollen carried by water currents.
o Example: Vallisneria, Hydrilla.
3.
Insects
(Entomophily):
o Bright petals, nectar, scent.
o Example: Sunflower, rose.
4.
Birds
(Ornithophily):
o Large, colored flowers with nectar.
o Example: Hibiscus.
These adaptations ensure successful pollination.
8. Describe various outbreeding
devices used by plants.
Answer:
Plants prevent self-pollination by:
1.
Dichogamy: Stigma and anther mature at
different times (e.g., sunflower).
2.
Herkogamy: Physical barrier prevents self-pollination
(e.g., hibiscus).
3.
Self-incompatibility: Genetic mechanism rejects own
pollen.
4.
Unisexuality: Male and female flowers on
different plants (e.g., papaya).
These ensure cross-pollination and genetic variation.
9. What are artificial hybridization
techniques? Explain the steps involved.
Answer:
Used in plant breeding to produce improved varieties.
Steps:
1.
Selection: Choose parents with desired traits.
2.
Emasculation: Remove anthers before pollen
release.
3.
Bagging: Cover flower to prevent unwanted pollen.
4.
Pollination: Introduce desired pollen.
5.
Re-bagging: Cover again till fruit sets.
This ensures controlled cross-pollination.
10. Explain the process of
pollen-pistil interaction and pollen tube growth.
Answer:
- Pollen lands on stigma →
hydrates → germinates → pollen tube grows through style.
- Tube guided by chemicals
secreted by synergids (filiform apparatus).
- Carries two male gametes
to ovule.
- One fuses with egg (zygote),
other with polar nuclei (endosperm).
This interaction ensures compatibility and fertilization.
11. Describe the process of double
fertilization and its significance.
Answer:
Process:
1.
Pollen
tube releases two male gametes.
2.
One
gamete + egg → zygote (syngamy).
3.
Other
gamete + two polar nuclei → primary endosperm nucleus (triple fusion).
Significance:
- Ensures formation of embryo
and endosperm simultaneously.
- Endosperm develops only after
fertilization (saves energy).
- Unique feature of angiosperms.
12. Explain the structure and types
of endosperm.
Answer:
Structure:
- Develops from primary
endosperm nucleus (3n) after triple fusion.
Types:
1.
Nuclear: Free nuclei without cell walls
(e.g., coconut water).
2.
Cellular: Cell walls form after each division
(e.g., Datura).
3.
Helobial: Partly nuclear, partly cellular
(e.g., monocots).
Function:
Provides nutrition to the developing embryo.
13. Describe the stages of embryo
development in flowering plants.
Answer:
- Zygote → pro-embryo → globular
→ heart-shaped → mature embryo.
- Mature dicot embryo has:
1.
Two
cotyledons
2.
Plumule
3.
Radicle
4.
Embryonal
axis
Embryogenesis establishes root and shoot axis of the new plant.
14. Describe the structure of dicot
and monocot seeds.
Answer:
Dicot Seed (Bean):
- Two cotyledons, embryo, hilum,
micropyle, seed coat.
- Cotyledons store food
(non-endospermic).
Monocot
Seed (Maize):
- Single cotyledon (scutellum),
endosperm, coleoptile, coleorhiza.
- Endospermic seed (food stored
in endosperm).
15. What are post-fertilization
changes in flowering plants?
Answer:
After fertilization:
- Zygote → embryo
- Primary endosperm nucleus →
endosperm
- Ovule → seed
- Ovary → fruit
- Integuments → seed coat
- Pericarp forms from ovary wall
- Hormones regulate these
transformations.
16. Explain the structure and
development of fruit.
Answer:
- Ovary enlarges to form fruit.
- Pericarp: May become fleshy (tomato) or
dry (pea).
- True fruit: From ovary only (mango).
- False fruit: From ovary + other floral
parts (apple).
- If fruit forms without
fertilization → parthenocarpic (seedless banana).
17. What is apomixis? Explain its
importance in agriculture.
Answer:
Definition: Formation of seeds without fertilization.
Types:
- Asexual reproduction through diploid cells of
ovule.
Importance:
1.
Produces
genetically identical offspring.
2.
Maintains
hybrid vigour.
3.
Reduces
cost of hybrid seed production.
Examples: Citrus, mango.
18. Define and explain polyembryony.
How is it beneficial?
Answer:
Definition: More than one embryo in a seed.
Causes:
- More than one egg fertilized.
- Embryo from
nucellus/integrument cells.
Examples: Citrus, mango.
Benefits: - Produces multiple seedlings
from one seed.
- Maintains uniform quality.
19. Describe the structure of a
mature embryo sac with a labeled diagram.
Answer:
- 7 cells, 8 nuclei:
- 1 egg + 2 synergids
(micropylar end)
- 3 antipodals (chalazal end)
- 1 central cell (2 polar
nuclei)
Functions: - Egg → zygote
- Polar nuclei → endosperm
- Synergids → guide pollen tube
📘 Diagram required in exam.
20. Explain seed dispersal and its
importance.
Answer:
Agents:
1.
Wind: Light seeds (cotton).
2.
Water: Buoyant seeds (coconut).
3.
Animals: Sticky or edible fruits (mango).
4.
Mechanical: Burst open (balsam).
Importance:
- Prevents competition.
- Colonizes new habitats.
- Maintains plant distribution.
21. Describe the process of seed
germination.
Answer:
Steps:
1.
Imbibition: Water absorbed through micropyle.
2.
Enzyme
activation:
Food digested.
3.
Radicle
emergence: Root
formation.
4.
Plumule
growth: Shoot
formation.
Conditions: Water, oxygen, temperature, viable seed.
It marks the start of a new plant’s life.
22. Explain differences between
pollen grain and ovule with their functions.
Answer:
|
Feature |
Pollen Grain |
Ovule |
|
Nature |
Male gametophyte |
Female megasporangium |
|
Function |
Carries male gametes |
Produces female gamete |
|
Structure |
Two cells, exine & intine |
Nucellus, integuments, micropyle |
|
Fate |
Produces pollen tube |
Becomes seed after fertilization |
23. Explain the role of hormones in
fruit and seed formation.
Answer:
- After fertilization, auxins,
cytokinins, and gibberellins promote fruit and seed growth.
- Gibberellins can induce parthenocarpy
(seedless fruits).
- Hormones regulate cell
division, elongation, and nutrient mobilization for seed
and fruit maturation.
24. Describe how
self-incompatibility helps in promoting cross-pollination.
Answer:
- Self-incompatibility is a genetic mechanism that
prevents self-pollen germination.
- The stigma or style chemically
rejects self-pollen.
- Ensures pollen from other plant
fertilizes ovule → promotes cross-pollination → increases genetic
variation.
Examples: Petunia, tobacco.
25. Compare the major
pre-fertilization and post-fertilization events in angiosperms.
Answer:
|
Stage |
Events |
Examples |
|
Pre-Fertilization |
Gametogenesis (formation of gametes), Pollination (pollen
transfer) |
Pollen, embryo sac |
|
Fertilization |
Double fertilization (syngamy + triple fusion) |
Angiosperms |
|
Post-Fertilization |
Zygote → embryo, Ovule → seed, Ovary → fruit |
Pea, mango |
