Master flower structure, microsporogenesis, megasporogenesis, pollination, double fertilisation, endosperm, embryo, seed, apomixis and polyembryony — with realistic diagrams, notes, MCQs, A-R, and PYQs.
Flower — the fascinating organ of angiosperms
The supplied textbook highlights his work in embryology, taxonomy and tissue culture, his contribution to the Department of Botany at Delhi, test-tube fertilisation and intra-ovarian pollination, and his role in bringing Biology textbooks to higher-secondary education.
Human beings have had an intimate relationship with flowers since time immemorial. Flowers are objects of aesthetic, ornamental, social, religious and cultural value .
Floriculture is the branch of horticulture concerned with the cultivation of flowering and ornamental plants for gardens and for the floral industry.
To a biologist, flowers are morphological and embryological marvels and the sites of sexual reproduction .
The two most important units of sexual reproduction in a flower are:
Before the flower appears, hormonal and structural changes initiate the differentiation of the floral primordium .
Male reproductive structures
A stamen has two parts:
The proximal end of the filament is attached to the thalamus or petal.
A typical microsporangium is surrounded by four wall layers :
Sequence: Sporogenous tissue → PMC (2n) → Meiosis → Microspore tetrad (4 microspores, each n) → separate → Pollen grains
| Feature | Details |
|---|---|
| Size | Spherical, 25–50 μm diameter |
| Exine | Sporopollenin — most resistant organic material |
| Germ pores | Apertures on exine |
| Intine | Cellulose + pectin |
| Cells | Two-celled in over 60% of angiosperms; remaining species may be shed in the three-celled stage. |
Pollen grains have to reach a receptive stigma before they lose viability. Viability varies with species and depends to some extent on temperature and humidity.
Rice and wheat: pollen may lose viability within about 30 minutes after release. In some members of Rosaceae, Leguminoseae and Solanaceae , pollen may remain viable for months. Large numbers of pollen grains can be stored for years in liquid nitrogen at −196°C as pollen banks for crop-breeding programmes.
Pollen grains show remarkable variation in size, shape, colour and surface architecture among species. Pollen grains of some plants can cause allergies such as asthma and bronchitis. Parthenium (carrot grass) is cited in the textbook as a notable pollen-allergy source.
Pollen from flowers such as pea, chickpea, Crotalaria, balsam or Vinca can be dusted onto a slide containing about 10% sugar solution and observed after roughly 15–30 minutes for pollen-tube emergence.
Mature Embryo Sac: 7 cells, 8 nuclei
Pollination — transfer of pollen grains from anther to stigma.
Chasmogamous flowers open and expose anthers and stigma. Cleistogamous flowers remain closed; anthers and stigma are close together, so they are invariably autogamous and provide assured seed-set even without pollinators. NCERT examples: Viola, Oxalis, Commelina .
| Agent | Adaptations | Examples |
|---|---|---|
| Wind | Light, non-sticky pollen; feathery stigma | Grasses, corn |
| Water | Rare; mucilaginous covering | Vallisneria, Zostera |
| Insects | Colourful, fragrant, nectar-rich; sticky pollen | Bees, butterflies, moths |
| Vertebrates | Birds, bats | Tropical flowers |
Pollen tube enters a synergid → two male gametes are released → syngamy forms the diploid zygote → triple fusion forms the triploid primary endosperm nucleus (PEN) → the central cell becomes the primary endosperm cell (PEC).
Endosperm development precedes embryo development.
Embryo (Dicot): 2 cotyledons + embryonal axis (epicotyl with plumule, hypocotyl with radicle).
Fruit: Ovary → Fruit; Ovary wall → Pericarp. Apple = false fruit (thalamus contributes). Banana = parthenocarpic.
After fertilisation, ovules mature into seeds and the ovary develops into a fruit. The ovary wall becomes the pericarp .
A seed is often described as a fertilised ovule . A typical angiosperm seed consists of seed coat(s), cotyledon(s) and embryonal axis. The micropyle remains as a small pore in the seed coat and helps entry of oxygen and water during germination.
| Term | Key point | Examples |
|---|---|---|
| Non-albuminous / ex-albuminous | Endosperm completely consumed during embryo development. | Pea, groundnut |
| Albuminous | Part of the endosperm persists in the mature seed. | Wheat, maize, barley, castor |
| Perisperm | Persistent remnant of nucellus. | Black pepper, beet |
| Seed dormancy | Embryo may remain inactive until moisture, oxygen and suitable temperature become available. | Important for storage |
Dicot: two cotyledons; epicotyl ends in plumule; hypocotyl ends in radicle. Monocot grass: one cotyledon called scutellum; coleoptile encloses the shoot apex and coleorrhiza encloses the radicle/root cap.
Apomixis — production of seeds without fertilisation. Found in Asteraceae, grasses, Citrus, Mango.
Importance: Hybrid seeds without segregation; farmers can reuse hybrid seeds; cost-effective.
Occurrence of more than one embryo in a seed. Common in Citrus and Mango (nucellar cells develop into embryos). Apomictic embryos are genetically identical to parent — they are clones .
In some species, a diploid egg cell can be formed without reduction division and develop into an embryo without fertilisation. In other cases, somatic cells such as nucellar cells around the embryo sac begin dividing and produce additional embryos.
Click "Show Answer" to reveal step-by-step solutions with marks
Q1. Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Male gametophyte (pollen grain) develops in the microsporangium (anther) .
Female gametophyte (embryo sac) develops in the megasporangium (ovule) .
Q2. Differentiate between microsporogenesis and megasporogenesis.
Microsporogenesis: Formation of microspores from PMC.
Megasporogenesis: Formation of megaspores from MMC.
Both occur by meiosis .
Microsporogenesis → Pollen grains .
Megasporogenesis → Embryo sac .
Q3. With a neat diagram explain the 7-celled, 8-nucleate nature of female gametophyte.
3 cells at micropylar end (2 synergids + 1 egg) + 3 antipodals at chalazal end + 1 large central cell = 7 cells.
Central cell has 2 polar nuclei; all others have 1 each → 8 nuclei total.
Q4. What is triple fusion? Where and how does it take place?
Triple fusion = fusion of 1 male gamete with 2 polar nuclei → PEN (3n).
Occurs in the central cell of embryo sac. 2nd male gamete migrates from synergid to central cell and fuses with 2 polar nuclei.
Select your answer and click "Check Answers"
1. The male reproductive organ of a flower is:
2. A typical anther is:
3. Which is the innermost wall layer of microsporangium?
4. Exine of pollen grain is made up of:
5. Pollen grains are shed at 2-celled stage in about:
6. Mature embryo sac is:
7. The filiform apparatus is found in:
8. Embryo sac develops from:
9. Transfer of pollen from anther to stigma of same flower is called:
10. Cleistogamous flowers are:
11. Which is the dominant biotic pollinating agent?
12. In double fertilisation, triple fusion produces:
13. Endosperm development precedes embryo development because:
14. Coconut water is:
15. Apple is called a false fruit because:
16. Emasculation is the removal of:
17. Production of seeds without fertilisation is called:
18. Polyembryony is commonly seen in:
19. Monosporic development of female gametophyte means:
20. Which structure guides the pollen tube into the synergid?
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is NOT the correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.
Q. Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Male gametophyte (pollen grain) → microsporangium (anther) .
Female gametophyte (embryo sac) → megasporangium (ovule) .
Q. What is triple fusion? Where and how does it take place?
Triple fusion = fusion of 1 male gamete with 2 polar nuclei → PEN (3n).
Occurs in central cell of embryo sac. 2nd male gamete migrates from synergid and fuses with 2 polar nuclei.
Q. With a neat diagram explain the 7-celled, 8-nucleate nature of female gametophyte.
3 cells at micropylar end (2 synergids + 1 egg) + 3 antipodals + 1 large central cell = 7 cells.
Central cell has 2 polar nuclei; all others have 1 each → 8 nuclei total.
Q. What is apomixis and what is its importance?
Apomixis = production of seeds without fertilisation.
• Hybrid seeds without segregation
• Farmers can reuse hybrid seeds
• Cost-effective; important in hybrid seed industry
Q. Explain the role of tapetum in the formation of pollen-grain wall.
Tapetum is the innermost wall layer. It:
Q. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Self-incompatibility = genetic mechanism preventing self-pollen from fertilising ovules.
Pistil inhibits pollen germination or pollen tube growth. No fertilisation → no seed.
Q. Differentiate between hypocotyl and epicotyl; coleoptile and coleorrhiza; integument and testa.
Hypocotyl: below cotyledons → ends in radicle.
Epicotyl: above cotyledons → ends in plumule.
Coleoptile: sheath enclosing shoot apex.
Coleorrhiza: sheath enclosing radicle + root cap.
Integument: ovule's protective envelope.
Testa: hardened outer seed coat.
Q. What is bagging technique? How is it useful in a plant breeding programme?
Bagging: covering emasculated flowers with butter paper bag to prevent contamination.
• Ensures only desired pollen is used
• Prevents unwanted pollen
• Allows controlled hybridisation experiments