🌸 Chapter 1
Sexual Reproduction in Flowering Plants
(4 Marks )
🌸 1. Explain the structure
of a mature anther with a labelled diagram.
Answer:
A mature anther is bilobed, each lobe having two microsporangia,
making four in total. Each microsporangium shows:
1.
Epidermis – outer protective layer
2.
Endothecium – helps in dehiscence
3.
Middle
layers –
degenerate to provide nutrition
4.
Tapetum – nutritive layer aiding pollen
development
Inside,
pollen mother cells undergo meiosis forming pollen tetrads.
📘 Diagram: Structure of bilobed anther showing four
microsporangia.
2. Describe the process of
microsporogenesis.
Answer:
- Occurs inside microsporangium
of anther.
- Microspore mother cell (2n) undergoes meiosis
forming four haploid microspores (n).
- These remain arranged in a tetrad.
- Each microspore matures into a pollen
grain (male gametophyte).
This ensures genetic variation and gamete formation for fertilization.
3. Describe the structure of a
mature pollen grain.
Answer:
A pollen grain has:
- Exine (outer wall): made of sporopollenin,
highly resistant.
- Intine (inner wall): thin, made of
cellulose and pectin.
- Two cells:
1.
Vegetative
cell – large, vacuolated with nucleus.
2.
Generative
cell – small, dense cytoplasm, divides
to form two male gametes.
Pollen grains are the carriers of male gametes.
4. Explain the structure and
formation of the female gametophyte (embryo sac).
Answer:
- Megaspore mother cell (MMC) in the ovule undergoes meiosis
to produce four haploid megaspores.
- Only one becomes functional.
- It undergoes three mitotic
divisions forming 8 nuclei and 7 cells:
- 1 egg cell + 2 synergids
(micropylar end)
- 3 antipodals (chalazal end)
- 1 central cell with two polar
nuclei
This is called the Polygonum type embryo sac.
5. Differentiate between autogamy,
geitonogamy, and xenogamy.
Answer:
|
Type |
Source of Pollen |
Example |
Genetic Nature |
|
Autogamy |
Same flower |
Pea |
Genetically same |
|
Geitonogamy |
Different flower, same plant |
Maize |
Functionally cross but genetically self |
|
Xenogamy |
Different plant |
Hibiscus |
Genetically different |
Cross-pollination
(xenogamy) leads to genetic variation.
6. Explain the different agents of
pollination with examples.
Answer:
1.
Anemophily
(Wind): Maize,
grass – produce light pollen, feathery stigma.
2.
Hydrophily
(Water):
Vallisneria – pollen carried by water currents.
3.
Entomophily
(Insects):
Sunflower, rose – bright color, nectar.
4.
Ornithophily
(Birds): Hibiscus
– brightly colored flowers.
Each adaptation ensures effective pollen transfer.
7. Describe the outbreeding devices
in plants.
Answer:
Plants use mechanisms to prevent self-pollination:
1.
Dichogamy: Anther and stigma mature at
different times.
2.
Herkogamy: Physical barrier between anther and
stigma.
3.
Self-incompatibility: Genetic mechanism prevents pollen
germination.
4.
Unisexuality: Male and female flowers on
different plants (dioecious).
These
promote cross-pollination and genetic diversity.
8. What is artificial hybridization?
Describe its steps.
Answer:
Artificial hybridization is a controlled pollination to obtain plants
with desirable traits.
Steps:
1.
Emasculation: Removal of anthers before pollen
release.
2.
Bagging: Covering flower to prevent unwanted
pollination.
3.
Pollination: Desired pollen dusted on stigma.
4.
Re-bagging: Flower covered until fruit sets.
Used in plant breeding programs.
9. Explain the process of
pollen-pistil interaction.
Answer:
1.
Pollen
lands on stigma and hydrates.
2.
Compatible pollen germinates, forming pollen
tube.
3.
Tube
grows through style under chemical guidance.
4.
Enters
ovule via micropyle (filiform apparatus).
5.
Delivers
two male gametes → fertilization.
It ensures compatibility and successful reproduction.
10. Explain the steps involved in
double fertilization.
Answer:
1.
Pollen
tube enters embryo sac through micropyle.
2.
Releases
two male gametes:
o One fuses with egg → zygote (2n)
(syngamy).
o Other fuses with two polar nuclei → endosperm
nucleus (3n) (triple fusion).
Thus, two fertilizations occur — a unique feature of angiosperms.
11. What are the post-fertilization
events in angiosperms?
Answer:
1.
Zygote
→ embryo
2.
Primary
endosperm nucleus → endosperm
3.
Ovule
→ seed
4.
Ovary
→ fruit
5.
Integuments
→ seed coat
These changes lead to the formation of the mature fruit and seed.
12. Explain the development of
endosperm in flowering plants.
Answer:
- After triple fusion, primary
endosperm nucleus (3n) divides to form endosperm.
- Types:
1.
Nuclear: No cell wall initially (e.g.,
coconut).
2.
Cellular: Cell wall after each division
(e.g., Datura).
3.
Helobial: Intermediate type (e.g., monocots).
- Provides nutrition to
developing embryo.
13. Describe the stages of embryo
development in a dicot plant.
Answer:
Stages:
1.
Zygote
→ pro-embryo → globular → heart-shaped → mature embryo.
2.
Mature
embryo consists of:
o Two cotyledons
o Embryonal axis
o Plumule (shoot tip)
o Radicle (root tip)
Embryogenesis establishes root-shoot axis for germination.
14. Describe the structure of a
dicot seed.
Answer:
- Seed coat: Outer testa and inner tegmen.
- Embryo: Two cotyledons and embryonal
axis.
- Hilum: Scar where ovule attached to
ovary.
- Micropyle: Allows water absorption during
germination.
- Food is stored in cotyledons
(non-endospermic).
15. How are fruits formed after
fertilization?
Answer:
- Ovary enlarges → fruit.
- Ovule → seeds.
- Pericarp develops from ovary
wall (may be fleshy or dry).
- Hormones like auxins and
gibberellins stimulate fruit growth.
If formed without fertilization → parthenocarpic fruit (e.g., banana).
16. Explain the structure of a
typical ovule.
Answer:
Parts of ovule:
1.
Funicle: Stalk attaching ovule to placenta.
2.
Nucellus: Contains MMC.
3.
Integuments: Protective layers forming micropyle.
4.
Micropyle: Opening for pollen tube entry.
5.
Chalaza: Base opposite to micropyle.
Ovule develops into seed after fertilization.
17. Explain apomixis and its
significance.
Answer:
- Apomixis: Formation of seeds without
fertilization.
- Offspring are genetically
identical to parent.
Significance:
1.
Maintains
hybrid vigour.
2.
Saves
cost of producing hybrid seeds each season.
3.
Used
in plant breeding (e.g., grasses, citrus).
18. Define polyembryony and explain
its causes.
Answer:
Polyembryony: Formation of more than one embryo in a single seed.
Causes:
1.
More
than one egg fertilized.
2.
Embryos
from nucellar or integumentary cells.
Examples: Citrus, mango.
It results in identical or genetically varied seedlings.
19. Describe the structure and
function of the carpel/pistil.
Answer:
Parts:
1.
Stigma: Sticky surface for pollen
reception.
2.
Style: Elongated tube connecting stigma
and ovary.
3.
Ovary: Contains ovules attached to
placenta.
Function: Produces female gametophyte and helps in fertilization and fruit
formation.
20. Explain the adaptations in
flowers for insect pollination.
Answer:
- Brightly colored petals.
- Fragrant smell.
- Nectar production.
- Sticky pollen and stigma.
- Larger pollen grains for easy
attachment.
These ensure effective pollination by attracting insects like bees and butterflies.
21. Describe the types of ovules
based on orientation.
Answer:
1.
Orthotropous: Straight ovule (Polygonum).
2.
Anatropous: Inverted, most common (mustard).
3.
Campylotropous: Curved ovule (Capsella).
4.
Amphitropous: Slightly curved (Alisma).
5.
Circinotropous: Funicle surrounds ovule (Opuntia).
22. What are the steps of
megasporogenesis and its outcome?
Answer:
- MMC (2n) in nucellus undergoes
meiosis → 4 megaspores (n).
- 3 degenerate, 1 functional
megaspore develops into embryo sac.
- Repeated mitosis forms 8 nuclei
and 7 cells (egg apparatus, antipodals, and central cell).
Outcome: Female gametophyte formation.
23. Differentiate between true and
false fruits with examples.
Answer:
|
Type |
Development |
Example |
|
True fruit |
From ovary only |
Mango, tomato |
|
False fruit |
From ovary and other floral parts |
Apple, strawberry |
Both
types protect and help in seed dispersal.
24. Explain how pollen grains are
preserved and used in plant breeding.
Answer:
- Pollen stored in liquid
nitrogen (-196°C) using cryopreservation.
- Used for future hybridization
programs.
- Maintains pollen viability
and prevents genetic loss.
Essential for crop improvement and genetic conservation.
25. Explain the process of seed
germination.
Answer:
1.
Imbibition: Seed absorbs water through micropyle.
2.
Enzyme
activation:
Stored food digested to soluble forms.
3.
Radicle
emergence: Forms
primary root.
4.
Plumule
elongation:
Forms shoot system.
Seed germination marks the beginning of a new plant life.
