Asexual Reproduction
No Partner Required🌱 Cloning Without a Partner
Asexual reproduction in plants produces offspring that are genetically identical to the parent (clones). It requires only one parent, no gametes, no pollination, and no fertilisation. It is faster and more energy-efficient than sexual reproduction — but produces no genetic variation, making the population vulnerable to disease or environmental change. Plants use a remarkable variety of vegetative structures to achieve this.
| Method | Structure Used | How It Works | Example |
|---|---|---|---|
| Runners (Stolons) | Horizontal stem growing along soil surface | Runner grows outward; nodes touch soil, form new roots and shoots; new plant separates from parent | Strawberry, spider plant, Bermuda grass |
| Rhizomes | Horizontal underground stem | Grows laterally underground; new shoots emerge from nodes at intervals | Ginger, iris, grasses, couch grass |
| Bulbs | Underground storage organ of fleshy leaf bases around a bud | Daughter bulbs (bulblets) form at base of parent bulb; separate and grow independently | Onion, garlic, tulip, daffodil |
| Corms | Swollen underground stem base | New cormlets form around parent corm; parent dies; cormlets grow into new plants | Freesia, gladiolus, taro |
| Tubers | Swollen underground stem or root for food storage | Each tuber has buds ("eyes") that sprout new shoots; planted sections each grow new plant | Potato (stem tuber), sweet potato (root tuber) |
| Leaf cuttings | Detached leaf | Leaf placed in moist soil; adventitious roots and shoots grow from leaf base or edge | Begonia, succulent (Kalanchoe), African violet |
| Budding / Grafting | Bud or shoot joined to rootstock | Scion (desired variety) attached to rootstock; vascular tissue fuses; scion uses rootstock's roots | Rose grafting, fruit tree propagation |
✅ Advantages of Asexual Reproduction
- Only one parent needed — no pollinator or mate required
- Faster — can rapidly colonise available space
- More energy-efficient — no investment in flowers, nectar, or fruit
- Offspring identical to successful parent — all adapted to local conditions
- Useful in horticulture — preserves desirable traits (flavour, yield, disease resistance) exactly
❌ Disadvantages of Asexual Reproduction
- No genetic variation — all offspring identical (clones)
- Vulnerable to disease — a single pathogen can destroy entire population
- Cannot adapt to changing environments
- Offspring compete directly with parent for resources (same location, same niche)
- Limited dispersal — offspring usually very close to parent
Flower Structure
The Reproductive Masterpiece🌸 A Flower's Only Job Is Sex
A flower is a specialised reproductive shoot — every part exists to achieve one goal: successful fertilisation. The male parts produce pollen containing sperm cells; the female parts produce ovules containing eggs. The other structures (petals, sepals, nectaries) exist purely to attract pollinators or protect the reproductive structures. A flower that contains both male and female parts is bisexual (hermaphrodite); one with only male or female parts is unisexual.
Complete Reference
All Floral Parts — Structure & Function
Know every part, where it is, and exactly what it does. This is guaranteed exam content.
| Part | Location | Function | Male/Female/Neither |
|---|---|---|---|
| Receptacle | Base of flower; top of flower stalk (peduncle) | Supports all floral parts; may become part of fruit in some species (apple) | Neither |
| Sepal (collectively: calyx) | Outermost whorl; below petals | Protects flower bud before opening; usually green and leaf-like; may be coloured in some species | Neither (accessory) |
| Petal (collectively: corolla) | Second whorl; inside sepals | Attracts pollinators by colour, pattern (nectar guides), shape; may produce scent; protects inner parts | Neither (accessory) |
| Nectary | Base of petals or receptacle | Produces nectar — sugar-rich reward for pollinators; ensures pollinators visit and contact pollen | Neither (accessory) |
| Filament | Stalk of stamen, third whorl | Supports and positions the anther | ♂ Male |
| Anther | Top of filament (stamen = filament + anther) | Produces and releases pollen grains (contains male gametophyte/sperm cells); opens (dehisces) to release pollen | ♂ Male |
| Stigma | Top of carpel/pistil | Sticky/feathery surface that receives and traps pollen; may secrete chemical signals to recognise compatible pollen | ♀ Female |
| Style | Middle section of carpel, between stigma and ovary | Elevates stigma to improve pollen capture; pollen tube grows through style after landing on stigma | ♀ Female |
| Ovary | Swollen base of carpel | Contains one or more ovules (each with an egg cell); develops into FRUIT after fertilisation | ♀ Female |
| Ovule | Inside ovary | Contains the egg cell (female gamete); develops into SEED after fertilisation | ♀ Female |
⚠️ Exam Watch — The Critical Transformations After Fertilisation
After fertilisation, key structures change: Ovule → Seed (contains embryo + food store). Ovary wall → Fruit (pericarp — protects seed, aids dispersal). Ovary → Fruit. The style and stigma wither and fall off. Petals and sepals usually fall. These transformations are very commonly asked in exams. The carpel (pistil) = stigma + style + ovary = the entire female unit.
Comparison
Wind-pollinated vs Insect-pollinated Flowers
Different pollination strategies demand completely different flower designs. Know every feature and the reason for it.
| Feature | Wind-pollinated (Anemophilous) | Insect-pollinated (Entomophilous) |
|---|---|---|
| Petals | Small, dull, green/brown — no need to attract animals | Large, bright, conspicuous — attracts insects from a distance |
| Scent | None or very faint | Often strongly scented — additional attractant for insects |
| Nectar | None — no reward needed (no animals visit) | Produced — reward for pollinators to ensure they visit repeatedly |
| Pollen | Enormous quantities; very small, smooth, lightweight — designed to float in air | Less pollen; sticky, rough, spiky — adheres to insect body |
| Stamens | Long, exposed filaments; anthers hang outside flower; exposed to wind currents | Enclosed within flower; anthers positioned to deposit pollen on visiting insect |
| Stigma | Large, feathery, branched; hang outside flower; large surface area to catch airborne pollen | Small, sticky, inside flower; positioned to receive pollen from insect body |
| Position | Often flowers before leaves emerge (spring trees); leaves would block pollen | Any time — leaves irrelevant to pollination success |
| Examples | Grasses, maize, wheat, oak, birch, pine | Roses, sunflowers, proteas, ericas, orchids, fruit trees |
Pollination
Getting Pollen to the Right Place🐝 Pollination — Transfer, Not Fertilisation
Pollination is the transfer of pollen from the anther of one flower to the stigma of a flower of the same species. It is NOT the same as fertilisation — pollination is just delivery; fertilisation is the actual fusion of gametes. Pollination can be self-pollination (pollen to stigma of the same flower or plant) or cross-pollination (pollen to a different plant of the same species) — most plants strongly favour cross-pollination to maximise genetic diversity.
Key Distinction
Self-pollination vs Cross-pollination
One guarantees reproduction but limits variation. The other maximises variation but requires a partner.
🌼 Self-pollination
- Pollen from anther lands on stigma of the SAME flower or another flower on the SAME plant
- Produces offspring genetically identical (or very similar) to parent
- Advantages: guaranteed reproduction even without pollinators; quick; energy-efficient
- Disadvantages: reduces genetic variation; accumulates harmful mutations (inbreeding depression)
- Examples: wheat, rice, peas, tomatoes, many self-compatible orchids
🌸 Cross-pollination
- Pollen transferred to stigma of a DIFFERENT plant of the same species
- Produces genetically varied offspring — enhanced adaptability
- Advantages: genetic variation; hybrid vigour; reduces harmful mutations
- Disadvantages: depends on pollinators or wind; less certain; more energy investment
- Many plants have adaptations that prevent self-pollination: dichogamy (male and female parts mature at different times), self-incompatibility (chemical rejection of own pollen), heterostyly (different style lengths)
Agents of Pollination
Who Delivers the Pollen?
Wind and insects are the most common. But birds, bats, beetles, and even water play a role in some species.
| Agent | Flower Adaptations | SA Examples |
|---|---|---|
| Bees | Blue/violet/yellow flowers (bees can't see red); nectar guides (UV patterns); landing platforms; sweet scent; sticky pollen | Many fynbos species, ericas, wild rosemary |
| Butterflies | Bright red/orange/pink; upright posture; landing platform; sweet fragrance; narrow tube for proboscis | Buddleia, milkweeds, many garden flowers |
| Birds (sunbirds) | Red/orange tubular flowers; no scent (birds have poor smell); copious dilute nectar; sturdy flowers to support bird weight; pollen positioned on bird's head/back | Aloes, proteas, ericas, red-hot pokers (Kniphofia) |
| Wind | No petals/colour/scent/nectar; huge pollen quantities; feathery stigmas; exposed anthers on long filaments | Grasses, maize, wheat, rye, rushes, most trees |
| Beetles | Large, open, bowl-shaped; strong fruity/spicy scent; pollen as reward (often no nectar); usually dull-coloured | Magnolias, some lilies, Cape sugarbirds visit some |
| Moths/Night insects | White or pale (visible at night); strongly sweet-scented especially at night; deep tubes | Night-flowering jasmine, some orchids |
📌 SA Biodiversity Context — Sunbird & Fynbos Mutualism
The Cape Sugarbird (Promerops cafer) and Orange-breasted Sunbird are specialised pollinators of proteas and ericas respectively. This is a classic mutualistic relationship — the bird gets nectar, the plant gets reliable cross-pollination. The decline of these birds through habitat loss threatens the reproduction of hundreds of fynbos plant species, demonstrating why animal pollinators are ecosystem engineers, not just visitors.
Fertilisation & Seed Development
From Pollen Grain to New Plant🌰 After Pollination — The Real Work Begins
Pollination is just delivery — a pollen grain landing on a stigma is only the beginning. The pollen grain must germinate, grow a pollen tube down through the style to the ovule, and deliver sperm cells to fertilise the egg. After fertilisation, the ovule develops into a seed and the ovary into a fruit. This whole process may take days to months depending on the species.
Step by Step
From Pollen Grain to Fertilisation
The pollen tube is one of biology's most remarkable structures — a living tube that can grow 30 cm through style tissue to reach the ovule.
1
Pollen lands on stigma — pollen grain (containing two cells: a tube cell and a generative cell) lands on the sticky surface of a compatible stigma. The stigma recognises compatible pollen by chemical signals.
2
Pollen grain germinates — the pollen grain absorbs water and nutrients from the stigma surface and begins to germinate. A pollen tube grows out of the pollen grain.
3
Pollen tube grows down the style — the tube cell directs pollen tube growth downward through the style tissue toward the ovary. The generative cell divides to form two sperm cells inside the growing tube.
4
Pollen tube enters ovule — the tube penetrates the ovary wall and enters the ovule through a small pore called the micropyle.
5
Double fertilisation (unique to angiosperms) — one sperm cell fuses with the egg cell → zygote (2n) → develops into embryo. The other sperm fuses with the central cell (2 polar nuclei) → triploid cell (3n) → develops into endosperm (food store for seed).
⚠️ Exam Watch — Double Fertilisation Is Unique to Angiosperms
Double fertilisation is one of the most examined facts about flowering plant reproduction. TWO sperm cells are delivered; BOTH fertilise something. Sperm 1 + egg → zygote (2n) → embryo. Sperm 2 + 2 polar nuclei → endosperm mother cell (3n) → endosperm (food reserve in seed). Gymnosperms do NOT have double fertilisation — they have only single fertilisation (sperm + egg → embryo). No endosperm formed this way in gymnosperms.
After Fertilisation
Seed & Fruit Development
The ovule becomes a seed; the ovary becomes a fruit. Know every part of a seed and what it develops from.
🌰 Seed Structure
- Testa (seed coat) — develops from outer layers of ovule; tough, protective; prevents water loss and pathogens
- Embryo — develops from zygote; contains: plumule (embryonic shoot), radicle (embryonic root), hypocotyl (embryonic stem), cotyledon(s)
- Endosperm — develops from triploid cell after double fertilisation; food store (starch, oils, proteins) for embryo during germination; in monocots, retained as endosperm; in dicots, often absorbed into cotyledons
- Cotyledon(s) — seed leaves; 1 in monocots, 2 in dicots; store or absorb food for germination
- Micropyle — small pore in testa; allows water entry to trigger germination
🍎 Fruit Types
- Fruit = mature ovary wall (pericarp) ± other flower parts
- Simple fruits — from single ovary: berries (tomato, grape), drupes (peach, avocado — fleshy with stone), capsules (poppy), nuts (acorn)
- Aggregate fruits — from many ovaries of one flower: strawberry, blackberry, raspberry
- Multiple fruits — from ovaries of many fused flowers: pineapple, mulberry, fig
- Note: some "fruits" are not botanical fruits — e.g. strawberry flesh = swollen receptacle; the actual fruits are the tiny "seeds" (achenes) on the surface
End of the Cycle
Seed Germination
Dormancy ends. The embryo wakes up and the radicle bursts out first. Three conditions are all essential.
💧 Three Requirements for Germination
- Water — enters through micropyle; rehydrates cells; activates enzymes; essential for all metabolic reactions; breaks dormancy
- Oxygen — needed for aerobic respiration to provide energy (ATP) for growth; the embryo is actively growing before it can photosynthesise
- Suitable temperature — enzymes have optimal temperature ranges; too cold = enzyme activity too slow; too hot = enzymes denatured
- Note: light is NOT required for germination (though it is needed for subsequent growth)
🌱 Sequence of Events
- Water absorbed → enzymes activated → food reserves (starch, oils) mobilised → energy released by respiration
- Radicle (embryonic root) emerges first — anchors seedling and begins absorbing water/minerals
- Hypocotyl elongates and pulls (or pushes) cotyledons above/below soil depending on type
- Plumule (embryonic shoot) emerges second — protected initially by coleoptile in monocots or hook-shaped hypocotyl in dicots
- First true leaves unfurl → photosynthesis begins → seedling becomes nutritionally independent
Seed Dispersal
Moving Without Moving🌬️ Why Seeds Must Travel
If seeds fell directly under the parent plant, they would compete with it (and each other) for light, water, and nutrients. Dispersal moves offspring away from the parent, reduces competition, allows colonisation of new habitats, and may bring seeds to the specific conditions they need to germinate. Plants have evolved extraordinary seed and fruit structures to exploit wind, water, animals, and explosive mechanisms.
Wind (Anemochory)
Light seeds or fruits with wings, plumes, or parachutes. Examples: dandelion (pappus), maple (winged samara), willow herb, milkweed.
Water (Hydrochory)
Waterproof, buoyant seeds/fruits. Examples: coconut (fibrous husk traps air), mangroves, lotus. Can travel thousands of km by ocean currents.
Animals — Eaten (Endozoochory)
Fleshy nutritious fruit eaten; seeds pass through digestive tract undamaged, deposited elsewhere in faeces. Examples: berries, cherries, figs, wild olives.
Animals — Hooked (Epizoochory)
Hooks, barbs, or sticky surfaces catch on fur or clothing. Examples: burdock, "duiweltjie" (Tribulus), ticks' bur, grass awns.
Explosive (Autochory)
Fruit wall dries and tensions build until seed is explosively ejected. Examples: squirting cucumber, witch hazel, touch-me-not (Impatiens), peas.
Ants (Myrmecochory)
Seeds have elaiosome (fatty food body). Ants carry seeds to nest, eat elaiosome, discard seed underground — ideal germination site. Major in fynbos: proteas, ericas.
📌 SA Context — Ant Dispersal in Fynbos
Myrmecochory (ant dispersal) is exceptionally important in South African fynbos. Many proteas, ericas, and other fynbos plants produce seeds with elaiosomes — fatty, nutritious food bodies attached to the seed. Ants collect these seeds, carry them to underground nests, eat the elaiosome, and leave the seed buried underground. This is an ideal safe germination site — protected from fire above ground and from other seed predators. The invasion of fynbos by Argentine ants (Linepithema humile) is particularly devastating because Argentine ants eat the elaiosome on the spot rather than carrying seeds underground, effectively disrupting the dispersal mechanism for hundreds of plant species.
🎯 Plant Reproduction Assessment
Eight questions on how plants reproduce.
Question 1 of 8
What is the difference between pollination and fertilisation in plants?
Question 2 of 8
A grass flower has no petals, no scent, and no nectar, but produces massive quantities of very light, smooth pollen and has large feathery stigmas hanging outside the flower. What do these adaptations tell you about the grass's pollination strategy?
Question 3 of 8
What is double fertilisation, and why is it significant? In which plant group does it occur?
Question 4 of 8
After fertilisation in an angiosperm, what does each of the following develop into: (a) the ovule, (b) the ovary wall?
Question 5 of 8
Give TWO advantages and ONE disadvantage of asexual reproduction in plants.
Question 6 of 8
What are the THREE conditions necessary for seed germination? Explain why each is needed.
Question 7 of 8
Why is cross-pollination generally favoured over self-pollination by most plant species? What mechanisms do plants use to prevent self-pollination?
Question 8 of 8
Many fynbos plants (like proteas) have seeds dispersed by ants — a process called myrmecochory. Explain how this works and why the invasion of the Argentine ant threatens fynbos plant reproduction.