Asexual reproduction and vegetative propagation
Std 11 covered flower structure and cell division; here we study pollination, double fertilization, seed and fruit in detail.
A cut rose stem grows into a new plant without seeds, identical to the parent.
Asexual reproduction = offspring from a single parent without fusion of gametes, genetically identical (clones).
In the figure : Asexual reproduction and vegetative propagation.
Rule 1 : Asexual reproduction in lower organisms — Fragmentation: pieces of Spirogyra become new individuals. Budding: buds on yeast, Protosiphon separate. Spore formation: motile zoospores of Chlamydomonas. Others: binary fission (Chlorella, diatoms), conidia (Penicillium), gemmae (Marchantia). Result: all offspring identical (clones).
- Easy : Clone = genetic copy.
- Medium : Yeast = budding.
- Exam-type (CET) : Spirogyra = fragmentation.
Rule 2 : Vegetative propagation — Natural: root (sweet potato, dahlia), leaf (Bryophyllum), stem (turmeric rhizome, potato tuber, onion bulb). Artificial: cutting (rose, Bougainvillea), grafting (scion = upper part, stock = rooted part; apple, rose; single bud = budding / bud grafting), tissue culture (many plantlets from a small tissue; micropropagation). Advantage: desired variety is kept, quick growth. Drawback: no variation.
- Easy : Scion above; stock below.
- Medium : Tissue culture = micropropagation.
- Exam-type (CET) : Vegetative plants copy the parent.
F-B-S: Fragmentation, Budding, Spores. Scion sits on top of stock.
‘Yeast budding = bud grafting’ is wrong (different). Trap: ‘vegetative propagation is sexual’ is wrong.
Memory clue : "Clone = copy; scion = shoot on top".
Spot the difference
| Method | Example |
|---|---|
| Fragmentation | Spirogyra |
| Budding | Yeast |
| Zoospores | Chlamydomonas |
| Grafting | Apple, rose |
Practice questions
- 1What is a clone?
- 2Reproduction in yeast?
- 3Spores of Chlamydomonas?
- 4Bryophyllum reproduces by?
- 5What is a scion?
- 6Example of cutting?
- 7Advantage of tissue culture?
- 8Drawback of vegetative propagation?
Show answers (try them yourself first)
- 1Genetically identical offspring.
- 2Budding.
- 3Zoospores.
- 4Leaves.
- 5The joined upper part.
- 6Rose, Bougainvillea.
- 7Many plantlets from a small tissue.
- 8No variation.
Anther, microsporogenesis and male gametophyte
Pollen grains are tiny male 'carriers' with a very tough coat.
Microsporogenesis = meiosis of a microspore mother cell (2n) giving 4 haploid microspores (pollen grains). The pollen grain starts the male gametophyte.
In the figure : T.S. of anther and pollen grain.
Anther, microsporogenesis and male gametophyte
In the app you can move this figure with your finger.
Open in the appRule 1 : Structure of anther — Stamen = filament + connective + anther. The anther is usually dithecous (2 lobes) and tetrasporangiate (4 pollen sacs). Archesporial cell → inner sporogenous + outer parietal cell. Wall has 4 layers: epidermis (protective), endothecium (fibrous; helps dehiscence), middle layers, tapetum (innermost; nutritive). Sporogenous cells = microspore mother cells (MMC, 2n).
- Easy : Tapetum = nutritive layer.
- Medium : 4 pollen sacs = tetrasporangiate.
- Exam-type (CET) : Outside to in: E-E-M-T.
Rule 2 : Pollen grain and male gametophyte — Pollen grain: unicellular, haploid, non-motile; sporoderm = outer exine (sporopollenin; non-degradable; thin germ pores) + inner intine (cellulose + pectin). First mitosis: large vegetative cell + small generative cell; second mitosis of the generative cell gives 2 male gametes (in pollen or pollen tube). Most angiosperms shed pollen at the 2-celled stage. Viability: rice/wheat ~30 min, some families months.
- Easy : Exine tough; intine soft.
- Medium : Germ pore = tube exit point.
- Exam-type (CET) : 2 male gametes = non-motile.
Exine = EXternal; Intine = INternal.
‘Pollen is diploid’ is wrong (haploid). Trap: ‘tapetum is outermost’ is wrong (innermost).
Memory clue : "Tapetum = Tiffin — feeds the spores".
Spot the difference
| Layer | Role |
|---|---|
| Epidermis | Protection |
| Endothecium | Dehiscence |
| Tapetum | Nutrition |
Practice questions
- 1Pollen sacs in an anther?
- 2What is an MMC?
- 3From one MMC?
- 4Exine is made of?
- 5Role of germ pore?
- 6Intine is made of?
- 7Generative cell gives?
- 8Why do pollen fossils last?
Show answers (try them yourself first)
- 1Four.
- 2Microspore mother cell (2n).
- 34 microspores.
- 4Sporopollenin.
- 5Pollen tube emerges.
- 6Cellulose + pectin.
- 72 male gametes.
- 8Sporopollenin does not decay.
Ovule, megasporogenesis and embryo sac
The female gametophyte hides inside the ovule like a chick inside its shell.
Megasporogenesis = meiosis of a megaspore mother cell (2n) giving 4 haploid megaspores (1 functional). It develops into the embryo sac (female gametophyte).
In the figure : Anatropous ovule and embryo sac.
Ovule, megasporogenesis and embryo sac
In the app you can move this figure with your finger.
Open in the appRule 1 : Carpel and anatropous ovule — Carpel (megasporophyll) = ovary + style + stigma. Many free carpels = apocarpous (Michelia); fused = syncarpous (brinjal). Ovules: paddy, wheat, mango = uniovulate; tomato, lady's finger = multiovulate. Anatropous ovule: funicle → hilum; central nucellus; 2 integuments around; apical pore micropyle (next to funicle); opposite end chalaza.
- Easy : Micropyle = pore; chalaza = base.
- Medium : Integuments: 2.
- Exam-type (CET) : Anatropous = most common.
Rule 2 : Megasporogenesis and embryo sac — In the nucellus near the micropyle an MMC (2n) → meiosis → 4 linear megaspores; the upper 3 degenerate, the chalazal one is functional. It undergoes three free-nuclear mitoses → 8 nuclei (4 at each pole). One from each pole moves to the centre as polar nuclei. At the micropylar end: egg apparatus = 1 egg + 2 synergids (filiform apparatus guides the pollen tube); at the chalazal end: 3 antipodals. The 2 polar nuclei fuse to form the secondary nucleus (2n). Total 7 cells, 8 nuclei; from one megaspore = monosporic.
- Easy : 8 nuclei, 7 cells.
- Medium : Synergid = guide.
- Exam-type (CET) : Secondary nucleus = 2n.
3 + 2 + 3: egg apparatus 3, polar 2, antipodals 3 = 8.
‘8 cells in an embryo sac’ is wrong (7 cells, 8 nuclei). Trap: ‘all 4 megaspores function’ is wrong.
Memory clue : "Synergid = signpost for the pollen tube".
Spot the difference
| Part | Position |
|---|---|
| Egg apparatus | Micropylar |
| Antipodals | Chalazal |
| Polar nuclei | Centre |
Practice questions
- 1What is apocarpous?
- 2Example of uniovulate?
- 3What is the micropyle?
- 4How many megaspores function?
- 5Egg apparatus contains?
- 6Number of antipodals?
- 7Ploidy of secondary nucleus?
- 8What is monosporic?
Show answers (try them yourself first)
- 1Free carpels.
- 2Paddy, wheat, mango.
- 3Apical pore of the ovule.
- 4One.
- 51 egg + 2 synergids.
- 63.
- 72n.
- 8From a single megaspore.
Pollination types and agents
A bee visiting flowers carries pollen from one to another without knowing it.
Pollination = transfer of pollen from anther to stigma. Types: autogamy, geitonogamy, xenogamy; agents: wind, water, insects, birds.
In the figure : Pollination types and agents.
Rule 1 : Types of pollination — Autogamy: bisexual flower with its own pollen (pea, Clitoria); offspring identical. Cleistogamy: self-pollination without the flower opening (Commelina); homogamy: anther + stigma mature together; opening flowers = chasmogamous. Geitonogamy: onto another flower of the same plant; needs agents (like cross) but no genetic variation (pumpkin). Xenogamy: pollen from another plant; adds variation.
- Easy : Xeno = foreign; geiton = neighbour.
- Medium : Cleistogamy = closed flower.
- Exam-type (CET) : Geitonogamy = genetically self.
Rule 2 : Pollinating agents — Anemophily (wind; wheat, rice, maize, palms): small colourless flowers, no nectar/scent, light dry abundant pollen, feathery stigma, exserted stamens; hayfever. Hydrophily (~30 genera; Vallisneria, Zostera): unwettable pollen (mucilage); hypo- (under water; Zostera) / epi- (on surface; Vallisneria). Entomophily (rose, jasmine): large showy scented flowers, nectar, rough/sticky stigma, spiny pollen + pollen-kit; Salvia lever. Ornithophily (sunbirds; Bombax, Callistemon, Butea).
- Easy : Wind = light dry pollen.
- Medium : Entomophily = colour + scent + nectar.
- Exam-type (CET) : Hypo = below; epi = on top.
A-G-X: Autogamy = alone, geitonogamy = garden-mate, xenogamy = extra plant.
‘Geitonogamy gives variation’ is wrong (same plant). Trap: ‘all aquatic plants are hydrophilous’ is wrong.
Memory clue : "Wind = wheat; water = Vallisneria; bee = bright flower".
Spot the difference
| Agent | Feature | Example |
|---|---|---|
| Wind | light dry pollen | Maize |
| Water | unwettable pollen | Vallisneria |
| Insect | colour, scent, nectar | Rose |
| Bird | sunbird | Bombax |
Practice questions
- 1What is pollination?
- 2Example of autogamy?
- 3What is cleistogamy?
- 4Limit of geitonogamy?
- 5Stigma of wind-pollinated flower?
- 6Example of epihydrophily?
- 7What is pollen-kit?
- 8Agent in ornithophily?
Show answers (try them yourself first)
- 1Pollen from anther to stigma.
- 2Pea, Clitoria.
- 3Self-pollination in unopened flowers.
- 4No genetic variation.
- 5Feathery.
- 6Vallisneria.
- 7Sticky yellow coat on insect-pollinated pollen.
- 8Sunbirds.
Outbreeding devices and pollen–pistil interaction
Like avoiding close-relative marriages, plants avoid self-pollination to keep variation.
Outbreeding devices discourage self-pollination and promote cross-pollination. Pollen–pistil interaction = all events from pollen landing on the stigma to the pollen tube entering the ovule.
In the figure : Outbreeding devices and pollen–pistil interaction.
Rule 1 : Outbreeding devices — Unisexuality (monoecious: maize; dioecious: papaya, mulberry), dichogamy (protandry: androecium first — sunflower; protogyny: gynoecium first — Gloriosa), herkogamy (physical barrier; Calotropis), heterostyly (Primula; stigma/anther at different levels), self-incompatibility (genetic; tobacco, tea), prepotency (foreign pollen germinates faster; apple). Continued self-pollination = inbreeding depression.
- Easy : Protandry = male first.
- Medium : Herkogamy = barrier.
- Exam-type (CET) : Self-incompatibility = genetic.
Rule 2 : Pollen–pistil interaction — Pollination does not guarantee correct pollen; the pistil recognises compatible (same-species) pollen (specific proteins) and rejects wrong ones. Compatible pollen takes water/nutrients, germinates and the pollen tube, guided by chemicals, grows stigma → style → ovary → ovule, entering a synergid and bursting to release male gametes. Even compatible pollen compete. In vitro, sucrose + boric acid induce germination. Artificial hybridization: emasculation (remove anthers) + bagging, then desired pollen.
- Easy : Compatible = same species.
- Medium : Tube: stigma → synergid.
- Exam-type (CET) : Emasculation = removing anthers.
Protandry = andro (male) first; protogyny = gyno (female) first.
‘Self-incompatibility is physical’ is wrong (genetic). Trap: ‘dichogamy = unisexual’ is wrong.
Memory clue : "Heterostyly = Height difference of styles".
Spot the difference
| Device | Point | Example |
|---|---|---|
| Dichogamy | mature at different times | Sunflower |
| Herkogamy | physical barrier | Calotropis |
| Heterostyly | different levels | Primula |
| Dioecism | separate plants | Papaya |
Practice questions
- 1What is protandry?
- 2Example of protogyny?
- 3Example of dioecious?
- 4Where is herkogamy seen?
- 5What is inbreeding depression?
- 6Who rejects wrong pollen?
- 7What is emasculation?
- 8Where does the tube burst?
Show answers (try them yourself first)
- 1Androecium matures first.
- 2Gloriosa.
- 3Papaya, mulberry.
- 4Calotropis.
- 5Loss of vigour from continued selfing.
- 6The pistil (stigma).
- 7Removing anthers.
- 8In a synergid.
Double fertilization, endosperm and embryo
One pollen tube brings two male gametes that do two different jobs.
Double fertilization = syngamy (male gamete + egg → zygote 2n) + triple fusion (second male gamete + 2 polar nuclei → PEN 3n). Only in angiosperms; discovered by Nawaschin.
In the figure : Double fertilization and endosperm types.
Double fertilization, endosperm and embryo
In the app you can move this figure with your finger.
Open in the appRule 1 : Double fertilization — The pollen tube grows stigma → style → ovary → ovule, guided by synergid chemicals. Usually through the micropyle = porogamy; via the chalaza = chalazogamy; piercing integuments = mesogamy. The tube bursts in a synergid releasing 2 non-motile male gametes (siphonogamy). Syngamy (generative fertilization) → zygote 2n; triple fusion (vegetative fertilization) → PEN 3n → endosperm. Significance: food store is made only if fertilization happens; diploid state restored; avoids polyembryony.
- Easy : Syngamy = 2n; triple fusion = 3n.
- Medium : Porogamy = micropyle.
- Exam-type (CET) : Egg + 2 polar nuclei + 2 male gametes participate.
Rule 2 : Endosperm and embryo — Endosperm (3n): nuclear (most common; free nuclei then walls; coconut water + kernel, wheat), cellular (walls from the start; Petunia, Balsam), helobial (first transverse wall; Asphodelus). Maize = mosaic endosperm. Embryogenesis: zygote → 2-celled proembryo (suspensor initial + embryonal initial) → suspensor (6–10 cells) → octant → heart-shaped → horseshoe. Dicot: 2 cotyledons, plumule; monocot: 1 scutellum, coleoptile (sheath of plumule), coleorhiza (sheath of radicle). Both alike up to the octant.
- Easy : Nuclear is most common.
- Medium : Scutellum = monocot cotyledon.
- Exam-type (CET) : Endosperm first, embryo after.
Syngamy 2n = embryo; triple fusion 3n = food.
‘Endosperm is 2n’ is wrong (3n). Trap: ‘triple fusion uses 2 male gametes’ is wrong (one).
Memory clue : "Syngamy = the seed-to-be; triple fusion = the tiffin".
Spot the difference
| Event | Result | Ploidy |
|---|---|---|
| Syngamy | Zygote → embryo | 2n |
| Triple fusion | PEN → endosperm | 3n |
Practice questions
- 1Who discovered double fertilization?
- 2What is syngamy?
- 3Ploidy of PEN?
- 4What is porogamy?
- 5Example of nuclear endosperm?
- 6Role of suspensor?
- 7What is the scutellum?
- 8What is the coleoptile?
Show answers (try them yourself first)
- 1Nawaschin.
- 2Male gamete + egg.
- 33n.
- 4Tube enters via micropyle.
- 5Coconut, wheat.
- 6Pushes embryo into endosperm.
- 7Cotyledon of monocots.
- 8Sheath of the plumule.
Seed, fruit, apomixis and polyembryony
A banana has no seeds yet is a complete fruit; one mango stone can sprout more than one seedling.
After fertilization ovule → seed and ovary → fruit. Apomixis = seed without fertilization; parthenocarpy = fruit without fertilization; polyembryony = many embryos in one seed.
In the figure : Seed, fruit and special types.
Rule 1 : Seed and fruit — Integuments → seed coat (outer testa, inner tegmen); the micropyle remains as a small pore (water + O₂). Endospermic (albuminous) seeds: castor, coconut, maize; non-endospermic (ex-albuminous): pea, bean (embryo used up the endosperm; food in cotyledons). Persistent nucellus = perisperm (black pepper, beet). Fruit: triggered by seed hormones; ovary wall → pericarp (3 layers). Roles: nourish, protect, disperse. Dormancy = metabolic pause to survive adverse periods; seeds can stay viable for thousands of years.
- Easy : Testa outer; tegmen inner.
- Medium : Pea = non-endospermic.
- Exam-type (CET) : Perisperm = nucellus.
Rule 2 : Apomixis, parthenocarpy, polyembryony — Apomixis: embryo without meiosis and syngamy (mother-like plants); apogamy (from a gametophyte cell), apospory (gametophyte from a diploid sporophyte cell); recurrent (diplospory — Taraxacum), non-recurrent (Nicotiana), adventive embryony (from nucellus/integument; mango, orange, lemon). Parthenogenesis = embryo directly from egg. Parthenocarpy (Noll, 1902): banana, papaya, pineapple; auxin; artificial with gibberellin. Polyembryony (Leeuwenhoek 1719, Citrus): adventive or cleavage; improves survival.
- Easy : Apomixis = seed, no fertilization.
- Medium : Parthenocarpy = seedless fruit.
- Exam-type (CET) : Citrus = polyembryony.
Apomixis = no mixing of gametes; parthenocarpy = fruit with no seed.
‘Parthenocarpic fruit has seeds’ is wrong. Trap: ‘apomixis involves fertilization’ is wrong.
Memory clue : "Seed ← ovule; fruit ← ovary".
Spot the difference
| Term | Meaning |
|---|---|
| Apomixis | seed without fertilization |
| Parthenocarpy | fruit without fertilization |
| Polyembryony | many embryos |
Practice questions
- 1Seed develops from?
- 2Fruit develops from?
- 3Example of non-endospermic?
- 4What is perisperm?
- 5What is apomixis?
- 6Example of parthenocarpy?
- 7Where was polyembryony first seen?
- 8What is dormancy?
Show answers (try them yourself first)
- 1Ovule.
- 2Ovary.
- 3Pea, bean.
- 4Persistent nucellus.
- 5Seed without fertilization.
- 6Banana, papaya, pineapple.
- 7Citrus (Leeuwenhoek).
- 8Temporary metabolic arrest.
Quick revision of the whole lesson
| Concept | Key fact |
|---|---|
| Asexual | Clones; fragmentation, budding, spores |
| Anther | 4 sacs; tapetum; MMC → 4 pollen |
| Embryo sac | 7 cells, 8 nuclei |
| Pollination | Auto-, geitono-, xenogamy |
| Outbreeding | Dichogamy, herkogamy, heterostyly |
| Fertilization | Zygote 2n; PEN 3n |
| Seed/fruit | Apomixis, parthenocarpy, polyembryony |
🎯 Most important points for the exam
- Asexual and vegetative reproduction.
- T.S. of anther, pollen.
- Ovule and embryo sac.
- Pollination types/agents.
- Outbreeding devices.
- Double fertilization, endosperm.
- Seed, fruit, apomixis.
Understand the concept → draw the figure → memorise the key points → solve questions yourself.