Sexual Reproduction in Flowering Plants Class 12: Concepts, Diagrams and Board Answers

What Sexual Reproduction in Flowering Plants is about

Weightage: This chapter is part of Unit VI, Reproduction, which carries 16 of the 70 theory marks together with Human Reproduction and Reproductive Health.Source: CBSE Biology (044) syllabus 2026-27, course structure, Unit VI Reproduction

In real board papers: asked in 8 of the 8 board papers we hold (2023 to 2026), on average 9.3 marks per paper. See the questions

Key concepts

Stamen, microsporangium and microsporogenesis

NCERT section 1.2.1 Stamen, Microsporangium and Pollen Grain

A stamen has a long, slender filament and a terminal anther. A typical angiosperm anther is bilobed, each lobe with two thecae (dithecous), so a transverse section shows a four-sided structure with four microsporangia (pollen sacs).

Wall of the microsporangium (outside to inside): epidermis, endothecium, middle layers and tapetum. The outer three protect the anther and help it split (dehisce) to release pollen. The tapetum nourishes the developing pollen grains; its cells have dense cytoplasm and are often multinucleate.

In a young anther, the centre of each microsporangium has the sporogenous tissue. Each of its cells is a potential pollen mother cell (PMC) or microspore mother cell, which undergoes meiosis to form a microspore tetrad (four haploid cells). This process is microsporogenesis. When the anther matures and dries, the microspores separate and develop into pollen grains.

Worked example

Name the four wall layers of a microsporangium from outside to inside and state the function of the innermost layer. How many meiotic divisions are needed to produce 100 pollen grains? (2 marks)

Try it first, then show the solutionSolution

1. Epidermis, endothecium, middle layers, tapetum; the tapetum nourishes the developing pollen grains. (1)
2. Each meiosis of a pollen mother cell gives a tetrad of 4 microspores, each becoming one pollen grain.
3. 100 ÷ 4 = 25 meiotic divisions. (1)

Answer: Epidermis, endothecium, middle layers, tapetum (nourishes pollen); 25 meiotic divisions.

The pollen grain (male gametophyte)

NCERT section 1.2.1 Stamen, Microsporangium and Pollen Grain (The pollen grain)

Pollen grains are generally spherical, about 25–50 micrometres across, with a two-layered wall.

• The hard outer exine is made of sporopollenin, one of the most resistant organic materials: it withstands high temperatures and strong acids and alkalis, and no enzyme that degrades it is known. This is why pollen is well preserved as fossils. The exine has prominent apertures called germ pores, where sporopollenin is absent; the pollen tube emerges through them.
• The inner intine is thin and continuous, made of cellulose and pectin.

A mature pollen grain contains two cells: the large vegetative cell (abundant food reserve, large irregular nucleus) and the small, spindle-shaped generative cell, which floats in the vegetative cell's cytoplasm. In over 60% of angiosperms, pollen is shed at this 2-celled stage. In the rest, the generative cell divides mitotically to give two male gametes before shedding (3-celled stage).

Pollen and people: pollen of some plants (such as Parthenium or carrot grass) causes allergies and respiratory problems; pollen is also eaten as a food supplement. Viability varies: rice and wheat pollen lose viability within 30 minutes of release, while some members of Rosaceae, Leguminosae and Solanaceae stay viable for months. Pollen can be stored for years in liquid nitrogen (−196 °C) in pollen banks, for crop breeding.

Worked example

Why are pollen grains well preserved as fossils? What is the role of germ pores? At what stage are pollen grains shed in most angiosperms? (3 marks)

Try it first, then show the solutionSolution

1. The exine is made of sporopollenin, which resists high temperature, strong acids, alkalis and enzymes, so pollen does not decay. (1)
2. Germ pores are apertures in the exine where sporopollenin is absent; the pollen tube comes out through them. (1)
3. In over 60% of angiosperms, pollen is shed at the 2-celled stage (vegetative cell + generative cell). (1)

Answer: Sporopollenin in the exine; germ pores allow the pollen tube to emerge; 2-celled stage.

Pistil, ovule, megasporogenesis and the embryo sac

NCERT section 1.2.2 The Pistil, Megasporangium (ovule) and Embryo sac

The gynoecium may have one pistil (monocarpellary) or more (multicarpellary); multiple pistils may be fused (syncarpous, as in Papaver) or free (apocarpous, as in Michelia). Each pistil has a stigma (landing platform for pollen), a style and a basal ovary, whose cavity (locule) contains ovules on the placenta. The number of ovules ranges from one (wheat, paddy, mango) to many (papaya, watermelon, orchids).

The ovule (megasporangium) is attached to the placenta by the funicle; the point of attachment is the hilum. It has one or two protective integuments, which leave a small opening, the micropyle; opposite it is the chalaza, the basal part. Inside the integuments is the nucellus, and within it the embryo sac (female gametophyte). An ovule generally has one embryo sac.

Megasporogenesis: a single megaspore mother cell (MMC) near the micropylar end of the nucellus divides by meiosis to give four megaspores. In most flowering plants, one megaspore is functional and three degenerate. This method of forming the embryo sac from a single megaspore is monosporic development.

Embryo sac development (female gametophyte): the functional megaspore nucleus divides mitotically three times (free-nuclear divisions) to give 2, 4 and then 8 nuclei. Cell walls then form, giving the typical mature embryo sac, 8-nucleate but 7-celled:

• Micropylar end: the egg apparatus: two synergids and one egg cell. The synergids have cellular thickenings at the micropylar tip called the filiform apparatus, which guides the pollen tube.
• Chalazal end: three antipodal cells.
• Centre: a large central cell with two polar nuclei.

Worked example

A mature embryo sac is described as '8-nucleate and 7-celled'. Explain this, and state how many mitotic divisions form it from the functional megaspore. (3 marks)

Try it first, then show the solutionSolution

1. The functional megaspore nucleus divides mitotically three times: 1 → 2 → 4 → 8 nuclei. (1)
2. Cells form around six nuclei: three at the micropylar end (egg + two synergids) and three at the chalazal end (antipodals). (1)
3. The remaining two polar nuclei share one large central cell, so there are 8 nuclei but 7 cells. (1)

Answer: Three free-nuclear mitoses give 8 nuclei; 6 single-nucleus cells plus 1 binucleate central cell make 7 cells.

Pollination and its agents

NCERT section 1.2.3 Pollination (kinds and agents of pollination)

Pollination is the transfer of pollen from the anther to the stigma of a pistil.

Kinds by source of pollen:

• Autogamy: pollen goes to the stigma of the same flower. It needs the anther and stigma to be close and to mature at the same time. Some plants, such as Viola (common pansy), Oxalis and Commelina, have two kinds of flowers: chasmogamous flowers (open, with exposed anthers and stigma) and cleistogamous flowers (never open). Cleistogamous flowers are invariably autogamous and produce assured seed set even without pollinators.
• Geitonogamy: pollen goes to the stigma of another flower of the same plant. It is functionally cross-pollination (needs an agent) but genetically like autogamy, because the pollen is from the same plant.
• Xenogamy: pollen goes to the stigma of a different plant. This is the only type that brings genetically different pollen to the stigma.

Agents:

• Abiotic: wind (most common; pollen is light and non-sticky, stamens well exposed, stigmas large and feathery, flowers often with a single ovule, as in grasses and corn cob tassels) and water (rare, mostly monocots: Vallisneria, Hydrilla, and the marine sea-grass Zostera). In Vallisneria, female flowers reach the water surface on long stalks and male flowers or pollen are released onto the surface. Water-pollinated flowers lack nectar and colour; their pollen is protected by mucilage.
• Biotic: mostly insects (especially bees), also birds, bats and other animals. Insect-pollinated flowers are large, colourful, fragrant and rich in nectar; small flowers are grouped in an inflorescence. Pollen and nectar are the usual floral rewards. Some plants give a safe place to lay eggs: the tallest flower, Amorphophallus (about 6 feet), and the Yucca moth, which cannot complete its life cycle without the plant, and vice versa.
• Pollen robbers consume pollen or nectar without pollinating.

Worked example

Distinguish between geitonogamy and xenogamy. Why is geitonogamy described as 'functionally cross-pollination but genetically similar to autogamy'? (2 marks)

Try it first, then show the solutionSolution

1. Geitonogamy: pollen from one flower to the stigma of another flower on the same plant; xenogamy: pollen to the stigma of a flower on a different plant. (1)
2. In geitonogamy an agent carries pollen between flowers, as in cross-pollination, but the pollen comes from the same plant, so it is genetically the same as self-pollination. (1)

Answer: Geitonogamy: same plant, different flower; xenogamy: different plant. Geitonogamy needs an agent (functional cross) but the pollen is genetically identical (like selfing).

Outbreeding devices, pollen–pistil interaction and artificial hybridisation

NCERT section 1.2.3 Pollination (Outbreeding devices; Pollen–pistil interaction; Artificial hybridisation)

Continued self-pollination causes inbreeding depression. Flowering plants have several outbreeding devices that discourage self-pollination and encourage cross-pollination:
1. Pollen release and stigma receptivity are not synchronised (one matures before the other).
2. The anther and stigma are placed at different positions, so pollen cannot reach the stigma of the same flower.
3. Self-incompatibility: a genetic mechanism that prevents self-pollen from fertilising ovules by inhibiting pollen germination or pollen tube growth in the pistil.
4. Unisexual flowers: if male and female flowers are on the same plant (monoecious, such as castor and maize), autogamy is prevented but not geitonogamy; if they are on different plants (dioecious, such as papaya), both autogamy and geitonogamy are prevented.

Pollen–pistil interaction: the pistil recognises compatible pollen and rejects incompatible pollen (of another species or self-pollen in self-incompatible plants), through chemical interaction between pollen and pistil. A compatible pollen grain germinates on the stigma and sends a pollen tube through a germ pore; the tube grows through the stigma and style to the ovary, enters the ovule through the micropyle and then enters one synergid through the filiform apparatus. All these events, from pollen landing to tube entry, form pollen–pistil interaction.

Artificial hybridisation (used to combine desired characters): only the desired pollen must reach the stigma.

• Emasculation: removing the anthers from a bisexual flower bud before the anther dehisces (with forceps).
• Bagging: covering emasculated flowers with a bag of butter paper to prevent contamination by unwanted pollen. When the stigma becomes receptive, desired pollen is dusted on it and the flower is rebagged.
• In unisexual flowers, emasculation is not needed; the female flower buds are bagged before they open.

Worked example

Explain how a monoecious plant like castor differs from a dioecious plant like papaya in preventing self-pollination. (2 marks)

Try it first, then show the solutionSolution

1. Castor (monoecious) has separate male and female flowers on the same plant: autogamy is impossible, but pollen can still reach another flower of the same plant (geitonogamy). (1)
2. Papaya (dioecious) has male and female flowers on different plants, so both autogamy and geitonogamy are prevented. (1)

Answer: Monoecy prevents autogamy only; dioecy prevents both autogamy and geitonogamy.

Double fertilisation

NCERT section 1.3 Double Fertilisation

After entering a synergid, the pollen tube releases two male gametes into the synergid's cytoplasm.

• One male gamete moves towards the egg cell and fuses with its nucleus: syngamy, giving a diploid zygote (2n).
• The other male gamete moves to the two polar nuclei in the central cell and fuses with them, giving a triploid primary endosperm nucleus (PEN, 3n). Because three haploid nuclei fuse, this is called triple fusion.

Since two kinds of fusion (syngamy and triple fusion) take place in one embryo sac, the event is called double fertilisation, a feature unique to flowering plants. The central cell becomes the primary endosperm cell (PEC), which develops into the endosperm, while the zygote develops into the embryo.

Ploidy checklist: nucellus, integuments, megaspore mother cell, zygote and embryo: 2n; megaspores, egg, synergids, antipodals, male gametes, pollen nuclei: n; primary endosperm nucleus and endosperm: 3n.

Worked example

The leaf cells of a flowering plant have 24 chromosomes. How many chromosomes are present in (a) a synergid, (b) the primary endosperm nucleus, (c) the zygote, (d) a nucellus cell? (2 marks)

Try it first, then show the solutionSolution

1. Leaf cells are diploid: 2n = 24, so n = 12.
2. (a) Synergid is haploid: 12. (½)
3. (b) PEN is triploid (two polar nuclei + one male gamete): 3n = 36. (½)
4. (c) Zygote is diploid: 24. (½)
5. (d) Nucellus is maternal diploid tissue: 24. (½)

Answer: (a) 12 (b) 36 (c) 24 (d) 24

Post-fertilisation events: endosperm, embryo, seed and fruit

NCERT section 1.4 Post-fertilisation: Structures and Events (1.4.1 Endosperm; 1.4.2 Embryo; 1.4.3 Seed)

Endosperm develops before the embryo, because the embryo needs nutrition from it. The PEN usually divides repeatedly without cell walls (free-nuclear endosperm); cell walls form later (cellular endosperm). The water of a tender coconut is free-nuclear endosperm (thousands of nuclei), and the white kernel around it is cellular endosperm. The endosperm may be used up completely before seed maturity (pea, groundnut, beans) or may persist in the mature seed (castor, coconut) to be used during germination.

Embryo: develops at the micropylar end from the zygote, after some endosperm has formed. Stages: proembryo, globular, heart-shaped and mature embryo.

• Dicot embryo: an embryonal axis with two cotyledons. The part above the cotyledons is the epicotyl, ending in the plumule (shoot tip); the part below is the hypocotyl, ending in the radicle (root tip), covered by a root cap.
• Monocot embryo (grass family): one cotyledon, the scutellum, on one side of the axis. The radicle and root cap are enclosed in a sheath, the coleorhiza; the shoot apex and a few leaf primordia are enclosed in a hollow foliar structure, the coleoptile.

Seed: the fertilised ovule, with seed coat(s), cotyledon(s) and embryo axis. Seeds are non-albuminous (no residual endosperm: pea, groundnut) or albuminous (endosperm remains: wheat, maize, barley, castor). In a few seeds such as black pepper and beet, remnants of the nucellus persist as perisperm. Integuments harden into the seed coat; the micropyle remains as a small pore that admits oxygen and water during germination. The seed loses water (moisture 10–15%), its metabolism slows and it may become dormant.

Fruit: the ovary wall becomes the pericarp. Fruits may be fleshy (guava, orange, mango) or dry (groundnut, mustard). True fruits develop only from the ovary; in false fruits (apple, strawberry, cashew) the thalamus also contributes. Parthenocarpic fruits (banana) develop without fertilisation and are seedless; parthenocarpy can be induced by growth hormones.

Significance of seeds: pollination and fertilisation are independent of water, so seed formation is more dependable; seeds have adaptations for dispersal to new habitats; they store food for the seedling; the hard coat protects the embryo; they carry new genetic combinations from sexual reproduction; and they are the basis of agriculture. Seeds can stay viable for long periods: a lupine (Lupinus arcticus) germinated after an estimated 10,000 years, and a 2000-year-old date palm (Phoenix dactylifera) seed was found viable.

Worked example

(a) Why does endosperm develop before the embryo? (b) What is perisperm? Give an example. (c) Why is an apple called a false fruit? (3 marks)

Try it first, then show the solutionSolution

1. (a) The developing embryo depends on the endosperm for nutrition, so the endosperm must form first. (1)
2. (b) Perisperm is the persistent remnant of the nucellus in the seed, as in black pepper and beet. (1)
3. (c) In apple, the thalamus also contributes to the fruit, not only the ovary. (1)

Answer: (a) Embryo needs nutrition from endosperm (b) persistent nucellus; black pepper, beet (c) thalamus contributes to the fruit.

Apomixis and polyembryony

NCERT section 1.5 Apomixis and Polyembryony

Apomixis is the formation of seeds without fertilisation; it is a form of asexual reproduction that mimics sexual reproduction. It occurs in some species of Asteraceae and grasses.

Ways it happens:

• A diploid egg cell forms without reduction division and develops into an embryo without fertilisation.
• More often (as in many Citrus and mango varieties), some cells of the nucellus around the embryo sac divide, protrude into the embryo sac and develop into embryos.

In such species each ovule may contain many embryos. The occurrence of more than one embryo in a seed is polyembryony (an orange seed squeezed open shows several embryos of different sizes).

Importance for agriculture: hybrid seeds must be produced fresh every year, because in their progeny the hybrid characters segregate and are lost. Producing hybrid seed every year is expensive for farmers. If hybrids are made apomictic, the characters do not segregate, and farmers can keep using the hybrid seed year after year. Scientists are trying to identify the genes for apomixis and transfer them into hybrid varieties.

Note the difference: parthenocarpy gives a fruit without fertilisation (seedless), while apomixis gives a seed without fertilisation.

Worked example

Why would making hybrid crops apomictic benefit farmers? (2 marks)

Try it first, then show the solutionSolution

1. Seeds of a hybrid, if produced sexually, give offspring in which hybrid characters segregate, so farmers must buy new hybrid seed every year, which is costly. (1)
2. Apomictic seeds form without fertilisation, so the embryo is genetically identical to the parent and the hybrid characters do not segregate; farmers can reuse their own seed. (1)

Answer: Apomixis prevents segregation of hybrid characters, so the same hybrid seed can be used every year without buying new seed.

Sexual Reproduction in Flowering Plants in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Microsporogenesis and the Pollen Grain
• Pollination and Outbreeding Devices
• Double Fertilisation and Post-fertilisation Events

Sexual Reproduction in Flowering Plants: key facts

Ploidy of structures

$\text{zygote, embryo, nucellus}=2n;\text{egg, synergids, antipodals, polar nucleus, male gamete}=n;\text{PEN, endosperm}=3n$

PEN = 2 polar nuclei (n + n) + 1 male gamete (n).

Meiosis counting

$1\text{PMC (meiosis)}\to 4\text{pollen};1\text{MMC (meiosis)}\to 1\text{functional megaspore}$

x pollen need x/4 meioses; x embryo sacs need x meioses.

Embryo sac formation

$1\text{megaspore}\stackrel{3\text{mitoses}}{\to }8\text{nuclei}\to 7\text{cells}$

Polygonum type: monosporic, 8-nucleate, 7-celled.

Double fertilisation

$\text{male gamete}+\text{egg}\to \text{zygote}(2n);\text{male gamete}+2\text{polar nuclei}\to \text{PEN}(3n)$

Syngamy plus triple fusion.

Pollination types

$\text{autogamy (same flower)};\text{geitonogamy (same plant)};\text{xenogamy (different plant)}$

Only xenogamy brings genetically different pollen.

Anther wall layers

$\text{epidermis}\to \text{endothecium}\to \text{middle layers}\to \text{tapetum}$

Outside to inside; tapetum nourishes pollen.

Sexual Reproduction in Flowering Plants: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Sexual Reproduction in Flowering Plants

The question patterns to expect, and the method that works for each.

Tricks to remember Sexual Reproduction in Flowering Plants

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Every Elephant Must Tiptoe

  Anther wall from outside in: Epidermis, Endothecium, Middle layers, Tapetum.

  Use it when: Labelling the T.S. of an anther.

• 3-3-2 in the embryo sac

  Micropylar end: 3 cells (egg + 2 synergids); chalazal end: 3 antipodals; middle: 2 polar nuclei in 1 central cell. 8 nuclei, 7 cells.

  Use it when: Drawing and describing the embryo sac.

• AGX: Auto, Geitono, Xeno

  Same flower, same plant, different plant: the circle widens from A to G to X.

  Use it when: Pollination types.

• Syngamy makes 2, triple fusion makes 3

  Egg + gamete = 2n zygote; 2 polar + gamete = 3n PEN.

  Use it when: Ploidy questions.

• Fruit without sex = Parthenocarpy; Seed without sex = Apomixis

  Parthenocarpy: no seeds (banana). Apomixis: seeds but no fertilisation (Citrus, mango).

  Use it when: Telling the two apart.

Sexual Reproduction in Flowering Plants: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Sexual Reproduction in Flowering Plants

The slips examiners see most often, and what to write instead.

• ✗Mistake: Calling the embryo sac 8-celled

  Wrong working

  The mature embryo sac has 8 cells: egg, 2 synergids, 3 antipodals and 2 polar cells.

  Right working

  It is 8-nucleate but 7-celled: the two polar nuclei lie in one central cell.

  ✓Do this: Count the central cell once.

  Usually costs: 1 mark.

• ✗Mistake: Wrong ploidy of endosperm or nucellus

  ✓Do this: Endosperm is 3n (two polar nuclei + one male gamete); nucellus is maternal 2n tissue.

  Usually costs: ½ mark per error.

• ✗Mistake: Saying monoecy prevents geitonogamy

  ✓Do this: Monoecy (castor, maize) prevents only autogamy; dioecy (papaya) prevents both autogamy and geitonogamy.

  Usually costs: 1 mark.

• ✗Mistake: Unlabelled micropylar and chalazal ends in diagrams

  ✓Do this: Always mark the micropyle and chalaza; the egg apparatus must be drawn at the micropylar end.

  Usually costs: ½ to 1 mark of diagram marks.

• ✗Mistake: Confusing apomixis with parthenocarpy

  ✓Do this: Apomixis gives seeds without fertilisation; parthenocarpy gives fruits without fertilisation (and without seeds).

  Usually costs: 1 mark.

NCERT exercise guide: Sexual Reproduction in Flowering Plants

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Sexual Reproduction in Flowering Plants: previous year questions

• Asked in 8 of the 8 board papers we hold (2023 to 2026), on average 9.3 marks per paper; 31 questions in all, counting OR alternatives. In 4 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Sexual Reproduction in Flowering Plants

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every Sexual Reproduction in Flowering Plants question, by year

Practice questions on Sexual Reproduction in Flowering Plants

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   The 7-celled, 8-nucleate embryo sac develops from:
   (a) a microspore (b) the megaspore mother cell directly (c) a functional megaspore (d) the nucellus

   Hint

   Monosporic development.

   Answer

   (c) a functional megaspore

2. Q2 · 1 mark · Assertion-reasonBoard level

   Assertion (A): Geitonogamy is genetically similar to autogamy.
   Reason (R): In geitonogamy, pollen grains come from the same plant.
   (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.

   Hint

   Which plant does the pollen come from?

   Answer

   (a)

3. Q3 · 2 marks · Very short answerBoard level

   Differentiate between a chasmogamous and a cleistogamous flower. Name a plant that bears both. (2 marks)

   Hint

   Open versus closed.

   Answer

   Chasmogamous flowers open and expose their anthers and stigma; cleistogamous flowers never open and are self-pollinated (1). Viola (or Oxalis, Commelina) bears both (1).

4. Q4 · 2 marks · Very short answerBoard level

   List two adaptations each of wind-pollinated and insect-pollinated flowers. (2 marks)

   Hint

   Light pollen versus colour and nectar.

   Answer

   Wind: light, non-sticky pollen in large amounts; exposed stamens and large feathery stigmas (1). Insect: large, colourful, fragrant flowers rich in nectar; sticky pollen or flowers grouped in inflorescences (1).

5. Q5 · 3 marks · Short answerHarder board level

   Describe the structure of a dicot embryo and compare it with a monocot (grass) embryo. (3 marks)

   Hint

   Cotyledons, scutellum, coleoptile, coleorhiza.

   Answer

   Dicot: embryonal axis with two cotyledons; epicotyl ending in plumule above them, hypocotyl ending in radicle with root cap below (1½). Grass: one cotyledon (scutellum) on one side; shoot apex and leaf primordia enclosed in the coleoptile; radicle and root cap enclosed in the coleorhiza (1½).

6. Q6 · 3 marks · Short answerHarder board level

   A plant has 2n = 16. How many chromosomes are present in its (a) microspore, (b) tapetal cell (diploid wall cell), (c) primary endosperm nucleus? How many meiotic divisions produce 400 pollen grains? (3 marks)

   Hint

   n = 8.

   Answer

   (a) 8 (½) (b) 16 (½) (c) 24 (1). 400 ÷ 4 = 100 meiotic divisions (1).

7. Q7 · 3 marks · Short answerHarder board level

   Explain pollen–pistil interaction. Why is it important? (3 marks)

   Hint

   Recognition, then tube growth.

   Answer

   The pistil recognises whether pollen is compatible (right species, not self-incompatible) through chemical signals between pollen and pistil (1). Compatible pollen germinates; the tube grows through stigma and style, enters the ovule by the micropyle and a synergid by the filiform apparatus; incompatible pollen is inhibited (1). It ensures only suitable pollen achieves fertilisation, and plant breeders can manipulate it to produce desired hybrids (1).

8. Q8 · 5 marks · Long answerHarder board level

   (a) Describe the development of endosperm and give the fate of the endosperm in pea and castor. (2) (b) Distinguish albuminous and non-albuminous seeds with examples. (1) (c) What is seed dormancy and why is it advantageous? (2) (5 marks)

   Hint

   Free-nuclear first; persists or is used up.

   Answer

   (a) The PEN divides repeatedly without walls (free-nuclear endosperm), later becoming cellular; it is completely used up by the developing embryo in pea but persists in the mature castor seed (2). (b) Albuminous seeds keep endosperm (castor, wheat); non-albuminous do not (pea, groundnut) (1). (c) As the seed matures it loses water (10–15% moisture) and its metabolism slows to an inactive state (dormancy) (1); this lets it survive unfavourable conditions and be dispersed and stored until conditions suit germination (1).

9. Q9 · 3 marks · Short answerHOTS / competency

   Suppose a farmer notices that his papaya trees never set fruit, though they flower every year. A botanist finds that all the trees are female. Explain the cause and suggest a remedy. (3 marks)

   Hint

   Papaya is dioecious.

   Answer

   Papaya is dioecious: male and female flowers are on different plants (1). With only female trees there is no pollen, so no pollination or fertilisation and no fruit set (1). Plant some male trees among them (or bring pollen from male plants) so that pollinators can carry pollen to the female flowers (1).

10. Q10 · 2 marks · Very short answerHOTS / competency

    A seedless banana and an apomictic mango seed both form without fertilisation. Explain the difference between them. (2 marks)

    Hint

    Fruit versus seed.

    Answer

    Banana is parthenocarpic: the fruit develops without fertilisation and has no seeds (1). In apomictic mango, a seed with an embryo forms without fertilisation, often from nucellar cells (1).

11. Q11 · 2 marks · Very short answerHarder board level

    Explain why the Yucca plant and the Yucca moth depend on each other. (2 marks)

    Hint

    Eggs and pollination.

    Answer

    The moth lays its eggs in the locule of the ovary and pollinates the flower while doing so (1). The plant cannot be pollinated without the moth, and the moth's larvae develop on the seeds, so neither can complete its life cycle without the other (1).

12. Q12 · 1 mark · MCQHarder board level

    Which of the following is a false fruit?
    (a) Mango (b) Strawberry (c) Guava (d) Orange

    Hint

    The thalamus contributes.

    Answer

    (b) Strawberry

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which layer of the anther wall nourishes pollen grains?Show answer

   The tapetum.

2. 2.What is sporopollenin?Show answer

   The highly resistant organic material of the pollen exine; no known enzyme degrades it.

3. 3.In what percentage of angiosperms is pollen shed at the 2-celled stage?Show answer

   Over 60%.

4. 4.What is the filiform apparatus and its role?Show answer

   Cellular thickenings at the micropylar tip of synergids that guide the pollen tube into the synergid.

5. 5.What are cleistogamous flowers?Show answer

   Flowers that never open; they are invariably autogamous and ensure seed set.

6. 6.Name two water-pollinated plants.Show answer

   Vallisneria and Hydrilla (fresh water), Zostera (marine sea-grass).

7. 7.What is triple fusion?Show answer

   Fusion of a male gamete with two polar nuclei to form the triploid primary endosperm nucleus.

8. 8.What are the coleoptile and coleorhiza?Show answer

   Sheaths enclosing the shoot apex (coleoptile) and the radicle and root cap (coleorhiza) of a monocot embryo.

9. 9.Give two examples of false fruits.Show answer

   Apple and strawberry (also cashew).

10. 10.What is polyembryony? Give an example.Show answer

    Presence of more than one embryo in a seed, as in Citrus.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you draw and label the T.S. of a mature anther?
• ☐Can you describe the structure of a pollen grain and explain why it fossilises well?
• ☐Can you draw a typical anatropous ovule and the 7-celled embryo sac?
• ☐Can you define autogamy, geitonogamy and xenogamy with examples?
• ☐Can you list four outbreeding devices?
• ☐Can you describe the steps of artificial hybridisation?
• ☐Can you explain double fertilisation and give the ploidy of zygote, PEN and endosperm?
• ☐Can you compare dicot and monocot embryos and explain apomixis and its value?

Sexual Reproduction in Flowering Plants: frequently asked questions