Plant ReproductionOxford AQA IGCSE Biology: Revision notes
Section 1
What are the key structures of a flowering plant?
A flower contains both male and female reproductive organs, along with other specialised structures:
Male reproductive parts:
- Stamen = the male reproductive organ, consisting of the anther and filament
- Anther = produces pollen (male gametes)
- Filament = stalk that supports the anther
Female reproductive parts:
- Carpel = the female reproductive organ, consisting of stigma, style and ovary
- Stigma = the tip of the carpel that receives pollen
- Style = tube connecting stigma to ovary
- Ovary = contains ovules (female gametes)
- Ovule = structure within the ovary that develops into seeds after fertilisation
Accessory structures:
- Sepals = small leaf-like structures that protect the flower bud
- Petals = coloured structures that attract pollinators
When describing flower structure in an exam, examiners expect you to name the parts and their locations within the flower. Use phrases like 'the anther is located at the top of the filament' to show you understand the spatial relationships.
Think of the carpel like a test tube: the stigma is the opening at the top that receives pollen, the style is the narrowed neck, and the ovary at the bottom is the bulbous base that holds the ovules (like seeds in a bottle).
Section 2
How does pollination and fertilisation lead to seed formation?
Pollination is the transfer of pollen from the anther to the stigma. There are two types:
- Self-pollination = pollen from the anther of one flower fertilises the stigma of the same flower or another flower on the same plant
- Cross-pollination = pollen from the anther of one plant fertilises the stigma of a flower on a different plant
Fertilisation process:
- Pollen grain lands on the stigma
- Pollen tube grows down through the style towards the ovule
- Male gamete (in pollen) fuses with female gamete (in ovule)
- Zygote is formed
Seed and fruit formation: After fertilisation, the ovule develops into a seed containing the embryo and stored food. The ovary develops into a fruit, which protects the seeds and aids dispersal. Different flowers produce different fruit types (berries, pods, nuts).
Examiners often ask you to describe the stages of fertilisation in sequence. Always mention: pollen lands on stigma → pollen tube grows → nucleus travels down → gametes fuse → zygote forms.
Students often confuse pollination with fertilisation. Pollination is just the transfer of pollen (can happen without fertilisation). Fertilisation is the actual fusion of gametes that only occurs after pollen tube growth.
Section 3
What are the differences between insect-pollinated and wind-pollinated flowers?
Flowers are adapted for their specific pollination method. Key differences:
| Feature | Insect-pollinated | Wind-pollinated |
|---|---|---|
| Petal colour | Brightly coloured | Small or no petals; dull green or brown |
| Scent | Strongly scented | Little or no scent |
| Nectar | Produces nectar as food reward | No nectar |
| Pollen | Sticky, heavy pollen | Light, dry, powdery pollen |
| Stigma | Short stigma, inside flower | Long, branched feathery stigma protruding from flower |
| Anther | Enclosed within flower | Anthers hang outside flower on long filaments |
| Flower size | Large, showy flowers | Small, inconspicuous flowers in clusters |
| Examples | Roses, bees orchids, foxgloves | Grasses, wheat, hazel trees |
Why these adaptations?
- Insect-pollinated flowers attract specific pollinators through colour, scent and nectar
- Wind-pollinated flowers release massive quantities of lightweight pollen to increase chance of wind dispersal to distant stigmas
In exam questions, describe adaptations by linking structure to function. For example: 'Wind-pollinated flowers have feathery stigmas to increase the surface area for catching wind-blown pollen' shows understanding, not just facts.
A student is shown a flower with bright red petals, a sweet smell, and nectar. Predict the pollinator: This flower is insect-pollinated because insects are attracted to bright colours (red petals), use scent to locate flowers (sweet smell), and feed on nectar. Wind pollinators don't need these features.
Section 4
How are seeds dispersed in nature?
After fertilisation, seeds must be dispersed away from the parent plant to reduce competition. There are three main dispersal methods:
Wind dispersal:
- Seeds have light structures: wings, hairs, or parachute-like designs
- Examples: sycamore seeds (helicopters), dandelion seeds (parachutes), tumbleweed
- Adaptation: low density allows wind to carry seeds far
Water dispersal:
- Seeds are contained in waterproof fruits that float
- Examples: coconut, water lily seeds
- Adaptation: watertight casing protects seeds during transport
Animal dispersal:
Ingestion (eating):
- Seeds eaten by animals are passed out in faeces away from parent plant
- Examples: berries (strawberry, raspberry), drupes (cherry)
- Adaptation: attractive fruit rewards the animal; seed coat is tough to survive digestion
Attachment (hitching a ride):
- Seeds have hooks, spines or sticky surfaces that attach to animal fur/feathers
- Examples: burrs (burdock), seeds with barbs (goosegrass)
- Adaptation: hooked or barbed structures cling to fur and are transported passively
When asked to identify a dispersal method, look for structural clues: wings/light hair = wind; waterproof coating = water; hooks/barbs = attachment; fleshy fruit = ingestion. Link the adaptation to the dispersal method in your answer.
Explain why a dandelion seed disperses by wind rather than water. Dandelion seeds have a lightweight parachute structure that allows them to float on air currents. Seeds lack a waterproof coating needed for water dispersal, and they don't have an attractive fruit to encourage animal dispersal.
Section 5
What are the natural and artificial methods of asexual reproduction in plants?
Asexual reproduction produces genetically identical offspring (clones) from a single parent plant, without gamete fusion.
Natural asexual reproduction methods:
-
Runners (stolons) = horizontal stems that grow along the ground and produce new plants at nodes where they touch soil
- Example: strawberry plants
-
Bulbs = underground food storage organs surrounded by protective scales; new bulbs grow from the parent bulb
- Example: onion, daffodil
-
Tubers = swollen underground stems that store food; new plants grow from eyes (buds) on the tuber surface
- Example: potato
Artificial asexual reproduction methods:
-
Cuttings = a section of stem is cut and placed in moist soil/water where roots develop from the cut end
- Used for: roses, geraniums, herbs
- Advantage: quick propagation of desirable plants
-
Grafting = scion (shoot) from one plant is joined to rootstock (root system) of another plant; they fuse and grow as one
- Used for: fruit trees (apple, pear)
- Advantage: combines desirable traits of both parents; produces fruit-bearing trees quickly
-
Tissue culture = small pieces of plant tissue are grown in nutrient medium in sterile conditions to produce many identical plants
- Used for: orchids, bananas, strawberries
- Advantage: rapid mass production of plants; preserves desirable traits; takes up minimal space
Examiners expect you to compare advantages of each method. For tissue culture, emphasise: rapid production of large numbers, genetic uniformity, space efficiency, and ability to preserve desirable plant traits.
Students often confuse tubers and bulbs. Remember: bulbs have fleshy protective scales (like onion layers); tubers are thickened stems with eyes/buds on the surface (like potato). Both are underground storage organs but different structures.
Section 6
What conditions are required for seed germination?
Germination is the process by which a seed grows into a seedling. Three essential conditions are required:
1. Water
- Needed to: activate enzymes; soften seed coat; enable metabolic reactions; transport dissolved nutrients
- Seeds are initially dormant (low water content); water uptake begins germination
- Too little water = seed remains dormant; too much = seed may rot
2. Oxygen
- Needed for: aerobic respiration to release energy for growth and metabolic processes
- Seeds respire to fuel the growth of the radical (root) and plumule (shoot)
- Seeds buried too deep or in waterlogged soil lack oxygen and will not germinate
3. Suitable temperature
- Different seeds have different temperature requirements (species-specific)
- Most germinate best at moderate temperatures (15–25°C)
- Temperature affects enzyme activity and respiration rate
- Too cold = slow respiration and growth; too hot = enzymes denature
Additional notes:
- These three conditions must be present simultaneously for germination to occur
- Light is NOT essential (many seeds germinate in darkness)
- Seed viability (ability to germinate) declines with age and poor storage conditions
Exam questions often ask 'why' seeds need each condition. Always explain the link to growth: water enables transport and enzyme activation; oxygen powers respiration for energy; temperature controls enzyme speed. Avoid just naming the conditions.
A farmer plants seeds but they fail to germinate. The soil is moist and the temperature is suitable (18°C). Suggest what is wrong: The soil may be waterlogged or compacted, preventing oxygen reaching the seeds. Seeds need aerobic respiration to release energy for growth, so lack of oxygen stops germination.
Must Know
- Flower structure: Stamens (anther + filament) produce pollen; carpels (stigma + style + ovary containing ovules) are female. Sepals protect; petals attract.
- Pollination and fertilisation: Pollen transfers to stigma (pollination); pollen tube grows down; male gamete fuses with female gamete forming zygote. Ovule becomes seed; ovary becomes fruit.
- Insect vs wind pollination: Insect flowers are colourful, scented, produce nectar, have sticky pollen and enclosed stamens. Wind flowers are dull, scentless, have dry powdery pollen and exposed stamens with feathery stigmas.
- Seed dispersal: Wind (light structures); water (waterproof fruits); animals via ingestion (fleshy fruit) or attachment (hooks/barbs).
- Asexual reproduction: Natural methods = runners, bulbs, tubers (all produce clones). Artificial methods = cuttings, grafting (joins scion to rootstock), tissue culture (rapid mass production).
- Germination requirements: Water (enables enzyme activity and transport), oxygen (powers respiration), suitable temperature (controls enzyme speed). All three must be present simultaneously.
That's the notes covered.
Carry on to the next subtopic.