Sexual Reproduction in Flowering Plants
Sexual reproduction in flowering plants is the IGCSE-only topic covering the structure of an insect-pollinated and a wind-pollinated flower, the mechanism of pollination, and the sequence of events from pollen landing on a stigma through to seed and fruit formation. Beyond GCSE Combined Science, Edexcel 4BI1 and Cambridge 0610/0970 require students to name the exact floral structures (anther, filament, stigma, style, ovary, ovule, sepal, petal, nectary) and explain how each is adapted to its method of pollination, then trace fertilisation as a named sequence: pollen tube growth down the style, the pollen tube nucleus and the male gamete nucleus travelling to the ovule, fusion of the male gamete nucleus with the egg cell nucleus to form a zygote, and the ovule developing into a seed while the ovary develops into a fruit.
Before you start
No specific prerequisites - this is a good place to start.
Method
- Draw and label a generalised flower, then sort the structures into male parts (anther on a filament, together the stamen, producing pollen grains containing the male gamete nucleus) and female parts (stigma, style, ovary containing one or more ovules, each ovule containing an egg cell nucleus).
- Compare an insect-pollinated flower with a wind-pollinated flower structure by structure: insect-pollinated flowers have large, brightly coloured petals, scent, nectar, and pollen that is sticky or spiky (to cling to a pollinator) and produced in small quantities; wind-pollinated flowers have small, dull or absent petals, no scent or nectar, anthers that hang loosely outside the flower on long filaments, feathery stigmas that hang outside the flower to catch airborne pollen, and pollen that is smooth, light and produced in huge quantities.
- Define pollination precisely: the transfer of pollen grains from the anther of one flower to the stigma of the same or a different flower. State that self-pollination is transfer within the same plant (or same flower) and cross-pollination is transfer between two genetically different plants of the same species, and that cross-pollination increases genetic variation.
- Give fertilisation as an ordered sequence, naming every structure: (1) a pollen grain lands on a compatible stigma and germinates, growing a pollen tube down through the style; (2) the pollen tube grows towards an ovule, guided towards the micropyle; (3) the pollen tube nucleus and the male gamete nucleus travel down the tube to the ovule; (4) the male gamete nucleus fuses with the egg cell nucleus inside the ovule to form a diploid zygote.
- After fertilisation, track what each structure becomes: the zygote divides to form an embryo; the ovule (as a whole) becomes the seed, with its outer layer becoming the testa (seed coat); the ovary wall becomes the fruit; the petals, stamens, stigma and style usually wither and fall away.
- For seed dispersal questions, link the fruit's structure to its dispersal method (wind: light with wings or a parachute of hairs; animal: fleshy and brightly coloured, or hooked to attach to fur; explosive: a pod that dries and splits, flinging seeds out) and explain why dispersal away from the parent plant reduces competition for light, water and nutrients.
- When a question gives an unfamiliar flower diagram or data table on pollen grain counts, apply the same insect- versus wind-pollinated criteria rather than trying to recall a specific named species.
Worked example
A student examines a flower and records: petals are small and green, there is no scent, the anthers hang outside the flower on long filaments, and the stigma is large and feathery and hangs outside the flower. Identify, with reasons, whether this flower is insect-pollinated or wind-pollinated, and describe what happens after a pollen grain from this species lands on a compatible stigma.
- List the features given: small green (not brightly coloured) petals, no scent, anthers outside the flower on long filaments, a large feathery stigma outside the flower.
- Compare each feature to the two pollination syndromes: small dull petals and no scent rule out attracting insects; anthers hanging outside the flower on long filaments releases pollen freely into the air; a large feathery stigma outside the flower is adapted to catch airborne pollen grains as they drift past.
- State the conclusion with the reason: the flower is wind-pollinated, because every listed feature increases the chance of pollen being released into, and caught from, the air rather than attracting an animal pollinator.
- Describe fertilisation as a sequence: the pollen grain germinates on the stigma and grows a pollen tube down the style towards an ovule in the ovary.
- Continue the sequence: the pollen tube nucleus and the male gamete nucleus move down the tube to the ovule, and the male gamete nucleus fuses with the egg cell nucleus to form a zygote.
- Final answer: this is a wind-pollinated flower (dull petals, no scent, exposed anthers and feathery stigma); after pollination, a pollen tube grows to the ovule and the male gamete nucleus fuses with the egg cell nucleus, forming a zygote that develops into a seed.
Practice questions
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Q1Name the part of the flower that produces pollen grains.Show answer
Answer: The anther.
Q2Name the part of the flower where the pollen tube grows towards, and state what it contains.Show answer
Answer: The ovule; it contains the egg cell nucleus (female gamete).
Q3State the difference between pollination and fertilisation.Show answer
Answer: Pollination is the transfer of pollen from an anther to a stigma; fertilisation is the fusion of the male gamete nucleus with the egg cell nucleus to form a zygote, which happens later, after the pollen tube has grown down the style.
Q4State two structural features of an insect-pollinated flower that a wind-pollinated flower usually lacks.Show answer
Answer: Large, brightly coloured petals and nectar (or scent); accept any two of: large/coloured petals, scent, nectar, sticky/spiky pollen produced in small amounts.
Q5State what the ovary wall develops into after fertilisation.Show answer
Answer: The fruit.
Q6A hazel tree produces about 4 million pollen grains per catkin, and its flowers have no petals or scent. Suggest why hazel produces so many more pollen grains than an insect-pollinated flower of similar size.Show answer
Answer: Wind pollination is inefficient/random, because pollen is released into the air rather than delivered directly to another flower by a pollinator, so producing huge numbers of pollen grains increases the chance that at least some land on a compatible stigma.
Exam-style questions
Written in the style of a IGCSE Science exam paper, with a full mark scheme.
State the name of the female gamete-containing structure in a flower, and state where it is found.
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A gardener counts the seeds produced by 20 flowers of a plant species after either self-pollination or cross-pollination. Self-pollinated flowers produced an average of 12 seeds per flower; cross-pollinated flowers produced an average of 19 seeds per flower. Calculate the percentage increase in average seed number from self-pollination to cross-pollination, and suggest one genetic reason for the difference.
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A student compares two flowers, X and Y. Flower X has large purple petals, produces nectar and has sticky pollen. Flower Y has small green petals, no nectar, and hanging anthers with light, smooth pollen. Explain how the structure of each flower is adapted to its method of pollination, and describe the sequence of events from pollen landing on a compatible stigma to fertilisation.
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Free printable worksheet
Want more practice on paper? Download the sexual reproduction in flowering plants worksheet pack - 8 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 1 of IGCSE Science Workbook, the whole course as one free printable PDF.
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