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Bio · Ch 2 · Class 12 Jump to section… Chapter Overview Key Terms The Flower Pollen & Microsporogenesis Ovule & Megasporogenesis Pollination Fertilization Endosperm & Embryo Seed & Fruit Apomixis & Polyembryony Lesson Summary NCERT Solutions MCQs 1-Mark Questions Short Answers Long Answers HOTS Board-Pattern Questions Revision Notes FAQs

NCERT · CBSE & State Boards · Class 12 Biology

Sexual Reproduction in Flowering Plants

A complete, no-skipped-steps revision guide — every concept explained simply, with labelled diagrams, NCERT solutions, MCQs, and the exact questions examiners love to repeat.

Flower structure Microsporogenesis Megasporogenesis Pollination Double fertilization Embryo & seed Apomixis

Why this chapter matters

Introduction

Flowers are not just decoration — they are the reproductive machinery of the plant. Every fruit and seed you eat is the end result of a precisely choreographed sequence of events that happens inside a flower: pollen grains forming, an egg cell waiting inside an ovule, pollination connecting the two, and finally a unique event called double fertilization that exists only in flowering plants (angiosperms).

This chapter is one of the highest-weightage chapters in the Class 12 Biology board exam. It is diagram-heavy, term-heavy, and sequence-heavy — which actually makes it very scoring once you understand the order in which things happen. This guide walks through that order step by step, the same way an examiner expects you to write it.

⚑ How to use this guide

Read the concepts once in order, label the diagrams yourself on paper, then jump straight to the MCQs and NCERT solutions to test recall before your exam.

At a glance

Chapter Overview

Aspect	Details
Main theme	Sexual reproduction process in angiosperms — from flower structure to seed and fruit formation
Big sub-topics	Flower structure → Pollen grain & anther → Ovule & megagametophyte → Pollination → Pollen–pistil interaction → Double fertilization → Post-fertilization events → Seed & fruit → Apomixis & polyembryony
Diagram-based questions	Very high — embryo sac, ovule L.S., anther T.S., pollen grain, mature embryo
Linked chapters	Builds on "Reproduction in Organisms" (Ch.1) and leads into "Molecular Basis of Inheritance"
Question style	Definitions, labelled diagrams, "differentiate between" pairs, reasoning ("why") questions

Vocabulary first

Key Terms You Must Know

Botany is a language. Once these words feel familiar, the rest of the chapter reads like a story.

Core terms used throughout the chapter

Term	Simple meaning
Androecium	The "male whorl" of a flower — all the stamens together
Gynoecium	The "female whorl" of a flower — the pistil/carpel(s)
Microsporogenesis	Formation of microspores (pollen) inside the anther by meiosis
Megasporogenesis	Formation of megaspores inside the ovule by meiosis
Gametophyte	The gamete-producing generation/structure (pollen grain = male gametophyte; embryo sac = female gametophyte)
Sporopollenin	The extremely tough chemical that makes up the pollen exine — resists heat, acids, and enzymes
Pollination	Transfer of pollen grains from anther to stigma
Pollen–pistil interaction	The "checking" process by which the stigma recognises compatible pollen
Syngamy	Fusion of one male gamete with the egg cell → forms the zygote
Triple fusion	Fusion of the second male gamete with the two polar nuclei → forms the endosperm
Double fertilization	Syngamy + triple fusion happening together — unique to flowering plants
Apomixis	Seed formation without fertilization (asexual, but seed-based)
Polyembryony	More than one embryo developing inside a single seed

Pre-fertilization · Part 1

The Flower: A Quick Structural Recap

A typical bisexual flower has four whorls arranged on a receptacle (thalamus):

• Calyx — sepals (usually green, protective)
• Corolla — petals (often colourful, attract pollinators)
• Androecium — stamens, the male reproductive whorl. Each stamen = filament + anther.
• Gynoecium — pistil(s)/carpel(s), the female reproductive whorl. Each pistil = stigma + style + ovary.

Fig. 1

Schematic L.S. of a flower showing the four whorls — calyx, corolla, androecium (stamen) and gynoecium (pistil)

Each anther is usually bilobed, and each lobe has two theca, so a typical anther has 4 microsporangia (called dithecous and tetrasporangiate). Each pistil has a swollen ovary containing one or more ovules attached to the placenta.

Pre-fertilization · Part 2

The Anther, Microsporogenesis & the Pollen Grain

1. Structure of the Microsporangium (anther lobe)

A transverse section of a young anther shows each microsporangium surrounded by four wall layers, from outside to inside:

1. Epidermis — protective outer layer
2. Endothecium — helps anther dehiscence (splitting open) at maturity
3. Middle layers (2–3 layers) — nutrition passage
4. Tapetum (innermost) — nourishes the developing pollen grains and supplies material for the pollen exine

Fig. 2

T.S. of a microsporangium showing the four wall layers and central sporogenous tissue

2. Microsporogenesis (formation of pollen grains)

The cells of the sporogenous tissue inside each microsporangium act as pollen mother cells (PMC / microspore mother cells). Each PMC undergoes meiosis to form a microspore tetrad (4 haploid microspores). This whole process — PMC → meiosis → microspores — is called microsporogenesis. As the anther matures, microspores separate from the tetrad and develop into pollen grains.

★ Correct developmental sequence

Sporogenous tissue → Microspore (pollen) mother cell → Meiosis → Microspore tetrad → Separated microspores → Pollen grain → Male gametes (after pollen germination)

3. Structure of a Pollen Grain

A mature pollen grain has two wall layers:

• Exine — hard outer wall made of sporopollenin, one of the most resistant organic materials known; withstands acids, alkalis, high temperature, and enzymes. Exine has germ pores where sporopollenin is absent.
• Intine — thin, continuous inner wall made of cellulose and pectin.

Inside, the pollen grain cytoplasm divides by mitosis into a large vegetative cell (rich in food reserves, forms the pollen tube) and a smaller generative cell (divides later to give two male gametes).

Fig. 3

A 2-celled pollen grain — exine, intine, vegetative cell and generative cell

Feature	Details
Shed at 2-celled stage	~60% of angiosperms (generative cell divides only after landing on stigma)
Shed at 3-celled stage	~40% of angiosperms — generative cell already divided into 2 male gametes before shedding (e.g. many cereals)
Viability	A few minutes (rice, wheat) to months (Rosaceae, Leguminosae, Solanaceae)
Allergy connection	Parthenium (carrot grass) pollen causes allergies and bronchial asthma in sensitive people
Pollen as food	Pollen tablets/syrups are marketed as nutritious supplements due to high protein content
Pollen storage	Pollen can be stored for years in liquid nitrogen (-196°C) — used to build "pollen banks", just like a seed/germplasm bank

⚑ Exam tip

"Explain the role of tapetum in pollen exine formation" is a frequently repeated NCERT-based question — remember tapetum nourishes pollen and supplies sporopollenin precursors for exine.

Pre-fertilization · Part 3

The Ovule & the Female Gametophyte (Embryo Sac)

1. Structure of a Typical Ovule

• Funicle — stalk attaching the ovule to the placenta
• Hilum — junction between funicle and ovule body
• Integument(s) — one or two protective layers around the nucellus
• Micropyle — small pore left at the tip where integuments don't fully close; the pollen tube usually enters here
• Nucellus — mass of cells with reserve food, encloses the embryo sac
• Chalaza — basal part of the ovule, opposite the micropyle
• Embryo sac (female gametophyte) — develops from a megaspore inside the nucellus

Fig. 4

L.S. of an anatropous ovule with the embryo sac embedded in the nucellus

2. Megasporogenesis

A cell near the micropylar end of the nucellus enlarges and differentiates into the megaspore mother cell (MMC). The MMC undergoes meiosis to form four haploid megaspores. In most flowering plants, only one megaspore stays functional — the other three degenerate. This is called monosporic development of the female gametophyte.

3. Development of the Female Gametophyte (7-Celled, 8-Nucleate Embryo Sac)

The functional megaspore's nucleus divides mitotically twice to form a 4-nucleate stage, then once more to form an 8-nucleate stage (4 nuclei at each pole). Cell walls then form around most nuclei, organising the mature embryo sac as follows:

1

Egg apparatus (micropylar end) — 1 egg cell + 2 synergids. Synergids have a special thickening at the tip called the filiform apparatus, which helps guide the pollen tube in.

2

Antipodal cells (chalazal end) — 3 cells, function not fully clear, may have nutritive role.

3

Central cell — the large remaining cell with 2 polar nuclei. These fuse (often before fertilization) to form a diploid secondary nucleus.

So: 4 (egg apparatus + central cell's 2 polar nuclei counted individually... ) — to avoid confusion, simply remember the count this way:

★ Memory anchor

8 nuclei total → grouped into 7 cells: 1 egg + 2 synergids + 3 antipodals + 1 central cell (which alone contains 2 polar nuclei). That's why it's called "7-celled, 8-nucleate."

Fig. 5

Mature female gametophyte (Polygonum-type embryo sac) — 7 cells, 8 nuclei

⚑ Exam tip

This embryo sac diagram with all parts labelled is one of the most frequently asked diagram questions in board exams — practise drawing and labelling it from memory.

Bringing the gametes together

Pollination, Outbreeding Devices & Pollen–Pistil Interaction

1. Types of Pollination

Type	Meaning
Autogamy	Self-pollination — pollen transfers within the same flower
Geitonogamy	Pollen from one flower lands on another flower of the same plant — genetically still self-pollination, but functionally needs a pollinator like cross-pollination
Xenogamy	Pollen from a flower of one plant reaches the stigma of a flower on a genetically different plant — true cross-pollination

Some flowers are cleistogamous (never open at all) — they are always self-pollinated since there is no chance for foreign pollen to enter.

2. Outbreeding Devices (preventing self-pollination)

Continuous self-pollination reduces genetic variation, so flowering plants have evolved devices to encourage cross-pollination:

• Dichogamy / Herkogamy — anther and stigma mature at different times, or are positioned so they don't contact each other in the same flower
• Self-incompatibility — a genetic mechanism that prevents pollen from the same flower/plant from fertilizing the ovule, even if it lands on the stigma
• Unisexual flowers — production of separate male and female flowers; dioecy (male and female flowers on different plants, e.g. papaya) stops both autogamy and geitonogamy; monoecy (e.g. cucurbits, maize) at least prevents autogamy

3. Agents of Pollination

Agent	Term	Notes
Wind	Anemophily	Pollen light, non-sticky; large feathery stigma (e.g. grasses)
Water	Hydrophily	Rare; seen in <30 genera, mostly monocots (e.g. Vallisneria, Zostera)
Insects	Entomophily	Most common biotic agent (e.g. bees)
Birds	Ornithophily	e.g. Bignonia
Bats	Chiropterophily	e.g. Kigelia, Adansonia

4. Pollen–Pistil Interaction

When pollen lands on a compatible stigma, it absorbs water and nutrients and germinates, producing a pollen tube that grows out through one of the germ pores. The tube grows down through the style, carrying the two male gametes, and usually enters the ovule through the micropyle (a route called porogamy). It enters one of the synergids and releases the two male gametes into its cytoplasm — setting up double fertilization.

⚑ Exam tip

"Bagging technique" in plant breeding (NCERT exercise) is used to prevent unwanted/contaminating pollen from reaching an emasculated flower — remember this links pollen–pistil interaction to applied plant breeding.

The defining event of angiosperms

Double Fertilization

Inside the embryo sac, the released male gametes take part in two fusion events at once:

1

Syngamy — one male gamete (n) fuses with the egg cell (n) → forms the diploid zygote (2n).

2

Triple fusion — the second male gamete fuses with the secondary nucleus (formed by fusion of the two polar nuclei) → forms the triploid primary endosperm nucleus (PEN, 3n). It is called "triple fusion" because three haploid nuclei (1 male gamete + 2 polar nuclei) are involved.

Because both fusions happen together in the same embryo sac, the overall event is called double fertilization — a phenomenon unique to flowering plants, first described by Nawaschin.

Fig. 6

Double fertilization — syngamy and triple fusion occurring together inside the embryo sac

Event	Gametes fused	Ploidy produced	Develops into
Syngamy	Male gamete + egg cell	2n (diploid)	Embryo
Triple fusion	Male gamete + 2 polar nuclei	3n (triploid)	Endosperm

After fertilization

Endosperm Development & Embryogeny

1. Endosperm Development

The PEN usually divides before the zygote does, so the endosperm forms first and nourishes the developing embryo. There are two patterns:

• Free-nuclear type — the PEN divides repeatedly without immediate wall formation, producing many free nuclei in a common cytoplasm; cell walls form later.
• Cellular type — a cell wall forms right after each nuclear division.

★ Classic NCERT example — coconut

The liquid "coconut water" is the endosperm at its free-nuclear stage; the white, edible kernel is the same endosperm once it has become cellular. This is why coconut water is considered nutritious — it is actually a nutrient-rich liquid endosperm.

2. Embryogeny (Dicot Embryo Development)

The zygote divides to form a proembryo: an upper/terminal cell that becomes the embryo proper, and a basal cell that elongates into a filamentous suspensor, which anchors the embryo and helps absorb nutrition. Further divisions produce, in order:

1

Globular stage — a rounded mass of cells

2

Heart-shaped stage — two lateral outgrowths appear; these become the cotyledons

3

Mature embryo — embryonal axis with cotyledons, plumule and radicle fully differentiated

3. Mature Dicot Embryo — Parts

Fig. 7

Mature dicot embryo — 2 cotyledons, epicotyl with plumule, hypocotyl, radicle

• Cotyledons — two, attached laterally to the embryonal axis (store/digest food)
• Epicotyl — part of axis above the cotyledon attachment; tip = plumule (shoot apex)
• Hypocotyl — part of axis below the cotyledon attachment; tip = radicle (root apex), covered by a root cap

Monocot embryo (e.g. grasses): a single large, shield-shaped cotyledon called the scutellum; radicle and root cap enclosed in a sheath called the coleorhiza; plumule enclosed in a sheath called the coleoptile.

The final product

Seed & Fruit Formation

1. The Seed

The ovule, after fertilization, matures into a seed. The integuments harden into the seed coat — outer testa and inner tegmen. The micropyle persists as a small pore that allows oxygen and water entry during germination. The hilum is the scar marking where the seed was attached to the fruit wall via the funicle.

Fig. 8

Structure of a mature (non-endospermous) dicot seed

Seed type	Description	Examples
Endospermous (albuminous)	Endosperm persists in mature seed, nourishes germinating seedling	Wheat, maize, barley, castor, coconut
Non-endospermous (non-albuminous)	Endosperm fully consumed during embryo development; food stored in cotyledons instead	Pea, gram, groundnut, bean, sunflower

Some seeds also keep a remnant of undigested nucellus called the perisperm (e.g. black pepper, beet). In castor, an extra structure called the caruncle (from the outer integument) sits near the micropyle and absorbs water.

2. The Fruit

The ovary develops into the fruit, and the ovary wall becomes the pericarp (sometimes differentiated into epicarp, mesocarp and endocarp).

• True fruit — develops from the ovary alone (e.g. mango, tomato)
• False fruit — develops from the ovary plus other floral parts such as the thalamus/receptacle (e.g. apple, strawberry, cashew)

Definition — Parthenocarpy

Development of fruit without fertilization, producing a seedless fruit. Occurs naturally in banana; can be induced artificially using growth-promoting hormones (e.g. auxins) in crops like tomato.

Beyond typical sexual reproduction

Apomixis & Polyembryony

Definition — Apomixis

A form of asexual reproduction that mimics sexual reproduction — seeds are produced without fertilization (e.g. some Asteraceae, certain grasses, Citrus). Plant breeders are working to introduce apomixis into hybrid crop varieties so that farmers don't need to buy fresh hybrid seed every season, since apomictic seeds reproduce the parent's traits faithfully without genetic segregation.

Definition — Polyembryony

The occurrence of more than one embryo in a single seed. In Citrus, this often happens because some nucellar cells (in addition to the egg) start dividing and form extra embryos — this is also called adventive embryony. It can also occur when both the egg cell and a synergid get fertilized.

Tie it together

Lesson Summary

1. A flower's androecium produces pollen (male gametophyte) via microsporogenesis; the gynoecium's ovule produces the embryo sac (female gametophyte) via megasporogenesis.
2. The mature embryo sac is 7-celled, 8-nucleate: 1 egg + 2 synergids + 3 antipodals + 1 central cell with 2 polar nuclei.
3. Pollination (autogamy/geitonogamy/xenogamy) is followed by pollen–pistil interaction, where the pollen tube grows through the style and enters the ovule, usually via the micropyle.
4. Double fertilization = syngamy (→ zygote, 2n) + triple fusion (→ PEN, 3n), happening together — unique to angiosperms.
5. The PEN develops into the nutritive endosperm; the zygote develops into the embryo through proembryo → globular → heart-shaped → mature stages.
6. The ovule becomes the seed (seed coat + embryo ± endosperm); the ovary becomes the fruit (true or false).
7. Apomixis and polyembryony are special reproductive variations of agricultural importance.

Textbook back-exercise

NCERT In-Text & Exercise Solutions

1. Name the parts of an angiosperm flower in which development of the male and female gametophytes takes place.

Male gametophyte (pollen grain) develops inside the microsporangium of the anther (part of the androecium). Female gametophyte (embryo sac) develops inside the ovule, located in the ovary (part of the gynoecium).

2. Differentiate between microsporogenesis and megasporogenesis. Mention the type of cell division involved, and the structure formed at the end of each.

Microsporogenesis: occurs in the anther; the pollen mother cell (PMC) undergoes meiosis to form a tetrad of microspores (pollen grains).
Megasporogenesis: occurs in the ovule; the megaspore mother cell (MMC) undergoes meiosis to form four megaspores, of which usually only one survives.
Both involve meiotic (reductional) division. Microsporogenesis ends with formation of pollen grains (microspores); megasporogenesis ends with formation of (functional) megaspores.

3. Arrange the following in the correct developmental sequence: pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes

4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

See Fig. 4 above. An ovule has a funicle (stalk), hilum (funicle–body junction), one or two integuments enclosing the nucellus, a micropyle (small opening at the tip), the chalaza (base, opposite the micropyle), and the embryo sac embedded inside the nucellus.

5. What is meant by monosporic development of the female gametophyte?

It means that the female gametophyte (embryo sac) develops from a single functional megaspore, while the other three megaspores formed during meiosis degenerate.

6. With a neat diagram, explain the 7-celled, 8-nucleate nature of the female gametophyte.

See Fig. 5 above. The functional megaspore nucleus divides mitotically to the 8-nucleate stage; cell walls then organise it into 1 egg cell + 2 synergids (egg apparatus) + 3 antipodal cells + 1 central cell containing 2 polar nuclei — i.e. 8 nuclei distributed in 7 cells.

7. What is the main objective of "bagging technique" used in emasculated flowers in a plant breeding programme?

Bagging covers the emasculated flower with a bag so that unwanted/contaminating pollen from other plants cannot reach the stigma, ensuring that only the deliberately chosen pollen fertilizes the flower.

8. Mention two strategies evolved to prevent self-pollination in flowers.

(i) Dichogamy/herkogamy — anther and stigma mature at different times or are positioned apart so self-pollen cannot reach the stigma of the same flower.
(ii) Self-incompatibility — a genetic mechanism that prevents self-pollen from fertilizing the ovule even after landing on the stigma. (Unisexuality — dioecy/monoecy — is another valid strategy.)

9. What is the significance of triple fusion?

Triple fusion (fusion of the second male gamete with the two polar nuclei) produces the triploid primary endosperm nucleus, which develops into the endosperm — the tissue that nourishes the developing embryo and, in many seeds, the germinating seedling.

10. Why do you think the zygote is dormant for a while in a fertilised ovule?

The zygote typically waits for the endosperm to form first, so that adequate nutrition is available before the embryo begins active development — this ensures the embryo has a ready food supply as it starts dividing.

11. Differentiate between syngamy and triple fusion.

Syngamy: fusion of one male gamete (n) with the egg cell (n) → forms the diploid zygote (2n) → develops into the embryo.
Triple fusion: fusion of the second male gamete (n) with the two polar nuclei (n+n) → forms the triploid PEN (3n) → develops into the endosperm.

12. Why do you think coconut water is a nutritious drink?

Coconut water is the liquid, free-nuclear endosperm of the coconut seed — it is rich in nutrients meant to nourish the developing embryo, which is why it is nutritious for humans too.

13. Why is apple or cashew not considered a "true fruit"? Which floral parts form these fruits?

They are false fruits because they develop mainly from the thalamus (receptacle), not the ovary alone. In apple, the fleshy edible part is the swollen thalamus, with the true fruit (ovary-derived core) inside. In cashew, the fleshy "apple" is the swollen peduncle/pedicel, while the actual ovary-derived fruit is the small kidney-shaped nut attached to it.

14. What is meant by emasculation? When and why does a plant breeder use this technique?

Emasculation is the removal of anthers from a bisexual flower bud before they mature/dehisce. A plant breeder uses this on the female parent in a cross-breeding programme to prevent self-pollination, so that only the desired pollen (collected separately) fertilizes the flower.

15. If one can induce parthenocarpy through the application of growth-promoting substances, what kind of fruits would they bear?

Such artificially induced parthenocarpic fruits would be seedless, since they develop without fertilization (no zygote/embryo/seed forms), even though the fruit itself develops normally.

16. Explain the role of tapetum in the formation of the pollen-grain exine wall.

The tapetum is the innermost wall layer of the microsporangium. It nourishes the developing pollen grains and also synthesises and secretes sporopollenin precursors, which are deposited on the developing microspore surface to form the highly resistant exine layer of the pollen wall.

⚑ Exam tip

For "differentiate between" type NCERT questions, always answer in a two-column comparison style (as above) — examiners award marks per correct point of distinction, not for a vague paragraph.

Quick self-test

MCQs (Tap to Reveal Answer)

1. The innermost wall layer of the microsporangium that nourishes the pollen grain is the

(a) Epidermis   (b) Endothecium   (c) Middle layer   (d) Tapetum

Answer: (d) Tapetum — it nourishes developing pollen and supplies sporopollenin for the exine.

2. A typical angiosperm anther is

(a) Monothecous, bisporangiate   (b) Dithecous, tetrasporangiate   (c) Dithecous, bisporangiate   (d) Monothecous, tetrasporangiate

Answer: (b) — two thecae, four microsporangia in total.

3. The chemical substance that makes the pollen exine highly resistant is

(a) Cellulose   (b) Pectin   (c) Sporopollenin   (d) Suberin

Answer: (c) Sporopollenin — resists high temperature, strong acids/alkalis, and enzymatic degradation.

4. The functional megaspore develops into the female gametophyte by undergoing

(a) Meiosis followed by mitosis   (b) Mitosis only   (c) Meiosis only   (d) No division

Answer: (b) Mitosis only — meiosis already occurred to produce the megaspores; the functional one then divides mitotically to the 8-nucleate stage.

5. The egg apparatus in a typical embryo sac consists of

(a) 1 egg + 3 antipodals   (b) 1 egg + 2 synergids   (c) 2 eggs + 1 synergid   (d) 1 egg + 2 polar nuclei

Answer: (b) — egg cell flanked by two synergids at the micropylar end.

6. The filiform apparatus is found in the

(a) Antipodal cells   (b) Synergids   (c) Central cell   (d) Egg cell

Answer: (b) Synergids — it helps guide the pollen tube into the embryo sac.

7. Triple fusion involves the fusion of

(a) 2 male gametes + 1 polar nucleus   (b) 1 male gamete + egg + synergid   (c) 1 male gamete + 2 polar nuclei   (d) 2 polar nuclei only

Answer: (c) — one male gamete fuses with the two polar nuclei to form the triploid PEN.

8. Pollination where pollen moves between two flowers on the same plant is called

(a) Autogamy   (b) Geitonogamy   (c) Xenogamy   (d) Hydrophily

Answer: (b) Geitonogamy — genetically equivalent to self-pollination, but functionally needs a pollinator.

9. Coconut water represents endosperm at the

(a) Cellular stage   (b) Free-nuclear stage   (c) Embryo stage   (d) Proembryo stage

Answer: (b) Free-nuclear stage.

10. Scutellum is a structure found in the embryo of

(a) Pea   (b) Gram   (c) Maize (a monocot)   (d) Castor

Answer: (c) Maize — scutellum is the single shield-shaped cotyledon of monocot (grass-family) embryos.

11. Seeds of which of these are non-endospermous (non-albuminous)?

(a) Wheat   (b) Castor   (c) Pea   (d) Coconut

Answer: (c) Pea — endosperm is consumed during embryo development; food is stored in cotyledons.

12. Apple is called a false fruit because it develops mainly from the

(a) Ovary wall   (b) Thalamus   (c) Sepals   (d) Style

Answer: (b) Thalamus (receptacle).

13. Seed formation without fertilization is termed

(a) Parthenocarpy   (b) Apomixis   (c) Polyembryony   (d) Geitonogamy

Answer: (b) Apomixis.

14. Pollen grains can be stored for years by preserving them in

(a) Distilled water   (b) Liquid nitrogen (-196°C)   (c) Formalin   (d) Saline at room temperature

Answer: (b) Liquid nitrogen (-196°C) — the basis of "pollen banks".

15. The pollen grain wall component made of cellulose and pectin is the

(a) Exine   (b) Intine   (c) Tapetum   (d) Sporopollenin layer

Answer: (b) Intine.

1-mark / very-short-answer

Most Expected Very Short Answer Questions

Q. Define pollination.1 mark

Transfer of pollen grains from the anther to the stigma of a flower.

Q. Name the chemical that makes pollen exine extremely resistant.1 mark

Sporopollenin.

Q. What is the female gametophyte of a flowering plant called?1 mark

Embryo sac.

Q. Name the cells that form the egg apparatus.1 mark

One egg cell and two synergids.

Q. What is the ploidy of the primary endosperm nucleus?1 mark

Triploid (3n).

Q. Define xenogamy.1 mark

Transfer of pollen from a flower of one plant to the stigma of a flower on a genetically different plant (true cross-pollination).

Q. Name the structure that guides the pollen tube into the synergid.1 mark

Filiform apparatus.

Q. Give one example each of a hydrophilous and an entomophilous plant.1 mark

Vallisneria (hydrophily); most bee-pollinated flowers, e.g. mustard (entomophily).

2–3 marks

Short Answer Questions

Q. Distinguish between autogamy, geitonogamy and xenogamy.3 marks

Autogamy = self-pollination within the same flower; geitonogamy = pollen transfer between two flowers of the same plant (genetically self, functionally cross); xenogamy = pollen transfer between flowers of two genetically different plants (true cross-pollination).

Q. What are outbreeding devices? Give two examples.2 marks

Mechanisms that prevent self-pollination/inbreeding and promote cross-pollination, e.g. (i) anther and stigma maturing at different times (dichogamy), (ii) self-incompatibility, (iii) unisexual flowers (dioecy/monoecy).

Q. Describe the structure of a typical dicot pollen grain.3 marks

Two-layered wall — outer sporopollenin exine (with germ pores) and inner cellulose-pectin intine; cytoplasm divided into a large vegetative cell and a small generative cell.

Q. What is meant by self-incompatibility?2 marks

A genetic mechanism that prevents self-pollen (or pollen from a genetically similar plant) from fertilizing the ovule, even though it may land and germinate on the stigma — it blocks fertilization, not pollination itself.

Q. Differentiate between a true fruit and a false fruit with one example each.2 marks

True fruit develops from the ovary alone (e.g. mango); false fruit develops from the ovary plus accessory floral parts like the thalamus (e.g. apple).

Q. Why are tapetal cells often multinucleate?2 marks

Tapetal cells need to actively synthesise and secrete large quantities of nutrients and sporopollenin precursors for the developing pollen grains, and being multinucleate supports this high metabolic/secretory activity.

5 marks

Long Answer Questions

Q. Describe the post-fertilization development of the endosperm and embryo in a dicot plant.5 marks

The primary endosperm nucleus (PEN, 3n) usually divides first, before the zygote, ensuring a nutrient supply is ready. It develops either by the free-nuclear pathway (repeated nuclear divisions without immediate walls, e.g. coconut water stage) or the cellular pathway (wall formation right after division). Meanwhile, the zygote divides to form a two-celled proembryo — a terminal cell (forms the embryo proper) and a basal cell (forms the suspensor, which anchors the embryo and aids nutrient absorption). Further division produces the globular stage, then the heart-shaped stage (two lateral cotyledon outgrowths appear), and finally the mature embryo with an embryonal axis: epicotyl (bearing the plumule) above, and hypocotyl (bearing the radicle and root cap) below the point of cotyledon attachment.

Q. With the help of a labelled diagram, describe the structure of the mature female gametophyte (embryo sac) in angiosperms.5 marks

See Fig. 5. The mature embryo sac is 7-celled and 8-nucleate. At the micropylar end lies the egg apparatus — one egg cell flanked by two synergids, the synergids bearing a filiform apparatus that guides the pollen tube. At the chalazal end lie three antipodal cells. The large central cell contains two polar nuclei, which usually fuse before fertilization to form a diploid secondary nucleus. This entire structure develops from a single functional megaspore through three successive mitotic divisions (monosporic development), followed by cellularisation.

Q. Explain double fertilization in flowering plants. Why is it considered unique to angiosperms?5 marks

After the pollen tube enters the embryo sac (usually via the micropyle) and releases its two male gametes into a synergid, two fusion events occur together: syngamy, where one male gamete fuses with the egg cell to form the diploid zygote; and triple fusion, where the second male gamete fuses with the two polar nuclei (already fused into the secondary nucleus, or fusing simultaneously) to form the triploid primary endosperm nucleus. Because both fusions occur in the same fertilization event, it is called double fertilization. This is unique to flowering plants because no other group of plants produces a triploid nutritive tissue (endosperm) through a second, simultaneous fusion alongside normal gamete fusion.

Higher Order Thinking

HOTS Questions

HOTS 1

Q. If the synergids of a flower are non-functional or destroyed, what is likely to happen during fertilization?
A. The pollen tube relies on the filiform apparatus of the synergids to be guided into the embryo sac and to release male gametes. Without functional synergids, the pollen tube may fail to enter the embryo sac correctly, and fertilization may not occur — reducing seed-set.

HOTS 2

Q. A plant produces seeds even when pollination is artificially prevented. What reproductive strategy does this indicate, and what would you expect about the seed's genetic makeup?
A. This indicates apomixis — seeds form without fertilization. Since no syngamy occurs, the resulting offspring would be genetically identical (or near-identical) to the mother plant, unlike normal sexually produced seeds.

HOTS 3

Q. Why might plant breeders consider apomixis highly valuable for the hybrid seed industry?
A. Hybrid seeds normally segregate in the next generation due to meiosis and recombination, so farmers must buy fresh hybrid seed every season. If apomixis could be engineered into hybrid varieties, the hybrid's superior traits would be passed on unchanged through seeds, removing the need to repurchase hybrid seed each year.

HOTS 4

Q. A seed shows two embryos on dissection. What term describes this, and suggest a possible cause.
A. This is polyembryony. A possible cause is that, besides the fertilized egg, an additional nucellar cell started dividing and developed into another embryo (adventive embryony) — commonly seen in Citrus.

Frequently repeated in board exams

Board-Pattern & Most Expected Exam Questions

These question formats recur across CBSE and State Board papers year after year — practise each one until you can answer without looking at notes.

• Draw a labelled diagram of a mature embryo sac / T.S. of anther / L.S. of ovule.
• Explain the role of tapetum in pollen wall formation.
• Describe the events of double fertilization with a diagram.
• Differentiate: autogamy vs geitonogamy vs xenogamy; syngamy vs triple fusion; true fruit vs false fruit; endospermous vs non-endospermous seed.
• What is self-incompatibility? Why is it considered an important outbreeding device?
• Explain the significance of the endosperm and describe its two patterns of development.
• Describe the structure of a typical anatropous ovule with a labelled diagram.
• What is apomixis? Discuss its importance in agriculture.
• Explain why coconut water and coconut "meat" represent two different stages of the same tissue.
• Define and distinguish between apomixis and parthenocarpy.

Examiners frequently combine a definition with a "why/significance" follow-up (e.g. "What is triple fusion? What is its significance?") — always pair your definition with the functional importance.

Night-before-exam recap

Quick Revision Notes

Anther side

Sporogenous tissue → PMC → meiosis → microspore tetrad → pollen grain (exine: sporopollenin; intine: cellulose+pectin) → vegetative cell + generative cell → 2 male gametes

Ovule side

MMC → meiosis → 4 megaspores → 1 functional (monosporic) → 3 mitotic divisions → 8 nuclei → 7 cells (egg+2 synergids, 3 antipodals, 1 central cell)

The fertilization equation to memorize

Male gamete + Egg cell = Zygote (2n) — Syngamy
Male gamete + 2 Polar nuclei = PEN (3n) — Triple fusion
Syngamy + Triple fusion = Double fertilization

Endosperm → Embryo → Seed → Fruit

PEN develops first into endosperm (free-nuclear or cellular) → nourishes the embryo as it grows from proembryo → globular → heart-shaped → mature stage → the whole ovule becomes the seed → the ovary becomes the fruit (true/false; may be parthenocarpic if seedless without fertilization).

Common doubts

Frequently Asked Questions

Why is the embryo sac called "7-celled, 8-nucleate" and not simply "8-celled"?

Because the central cell is counted as a single cell even though it contains two separate polar nuclei. So you have 7 distinct cells in total, but 8 nuclei when you count the central cell's two nuclei individually.

What's the real difference between pollination and fertilization?

Pollination is simply the physical transfer of pollen from anther to stigma — it does not guarantee fertilization. Fertilization is the actual fusion of gametes (syngamy/triple fusion) that happens later, only if the pollen is compatible and successfully germinates a pollen tube that reaches the embryo sac.

Is double fertilization the same as polyembryony?

No. Double fertilization refers to the two simultaneous fusion events (syngamy + triple fusion) inside one embryo sac that produce one zygote and one PEN. Polyembryony refers to more than one embryo developing in a single seed — a completely different phenomenon, sometimes not even involving fertilization at all (e.g. adventive embryony from nucellar cells).

Why do some seeds keep their endosperm (e.g. wheat) while others don't (e.g. pea)?

In non-endospermous (non-albuminous) seeds like pea and groundnut, the developing embryo consumes the endosperm completely and stores the food in its own cotyledons instead. In endospermous (albuminous) seeds like wheat and castor, the endosperm is not fully used up by the embryo and persists in the mature seed to nourish the seedling during germination.

Are apomixis and parthenocarpy the same thing?

No — they affect different structures. Apomixis is about seed formation without fertilization (asexual seed production). Parthenocarpy is about fruit formation without fertilization, producing a seedless fruit. A parthenocarpic fruit may have no seeds at all, while apomixis still produces seeds, just without the sexual fusion step.

Which diagrams are most important for the board exam from this chapter?

The mature embryo sac (7-celled, 8-nucleate), L.S. of a typical ovule, T.S. of a microsporangium/anther, structure of a pollen grain, and the mature dicot embryo are the five diagrams that appear most consistently across CBSE and State Board papers.

This guide follows the NCERT Class 12 Biology syllabus (Chapter: Sexual Reproduction in Flowering Plants) for CBSE and State Board exam preparation.
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