Form 5 · Paper 2 essay guide

Sexual Reproduction in Flowering Plants, Paper 2 essay guide

How Sexual Reproduction in Flowering Plants appears in Paper 2 essays: themes, a planning grid, a model answer structure and the keyword list.

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Essay themes this chapter supports

Describe flower structure and the formation of the pollen grain and embryo sac: Name the four whorls of a flower - sepals, petals, stamens, carpels - and state one function of each. → Describe pollen grain formation: pollen mother cell, meiosis, four microspores, tube nucleus and generative nucleus. → Describe embryo sac formation: embryo sac mother cell, meiosis, one surviving megaspore, three mitotic divisions to eight nuclei. → Name the cells and nuclei present in the mature embryo sac and their arrangement.
Explain pollination and double fertilisation in a flowering plant: Distinguish self-pollination from cross-pollination and name the agents involved in each. → Compare structural features of insect-pollinated and wind-pollinated flowers. → Describe pollen tube growth from the stigma to the ovule and its entry through the micropyle. → Explain double fertilisation: fusion forming the zygote, and fusion forming the endosperm nucleus.
Discuss the development, dispersal and germination of seeds: Explain how the ovule develops into a seed and the ovary into a fruit after fertilisation. → Compare a monocotyledonous seed with a dicotyledonous seed in terms of cotyledon number and food storage. → Describe the importance of seeds for survival, linking dormancy to unfavourable conditions and dispersal to reduced competition. → Name each method of seed dispersal with a structural adaptation and an example, then state the three conditions for germination.

How to structure your essay

Open with one or two sentences that define the topic and set the scope.
Devote one paragraph to each key concept, in a logical order.
Use precise biological terms and, where relevant, a labelled diagram.
Give an example or state where the process happens in the body or plant.
Close by linking the ideas back to the question.

Planning grid

Question	Answer
Introduction	Define sexual reproduction in a flowering plant as starting at the flower and ending at germination of a new seed.
Point 1	Flower structure: the four whorls and the function of each.
Point 2	Formation of the pollen grain and the embryo sac by meiosis.
Point 3	Pollination: self versus cross, and the structural features that match each agent.
Point 4	Double fertilisation: two fusions producing the zygote and the endosperm.
Point 5	Seed and fruit development: monocotyledonous versus dicotyledonous seeds.
Point 6	Importance of seeds, dispersal methods, and conditions for germination.
Conclusion	Link each stage back to the survival and spread of the flowering plant species.

Key terms to include

stamen
carpel
pollen mother cell
meiosis
embryo sac
polar nuclei
self-pollination
cross-pollination
pollen tube
double fertilisation
zygote
endosperm
testa
cotyledon
seed dispersal
germination

A model essay outline

Structure of a flower, The stamen, made up of the anther and filament, is the male reproductive part of a flower, while the carpel, made up of the stigma, style and ovary, is the female part; a single flower may contain one or more of each, and the number and arrangement of these parts is often used to identify a species. Some flowers, described as incomplete, lack one or more of these parts, such as petals or stamens, yet can still reproduce successfully.
Development of gametes, Pollen grains, each containing a male gamete, form inside the anther, while the embryo sac, containing the female gamete, forms inside the ovule within the ovary; both are produced by meiosis, which creates genetic variation among the gametes even before fertilisation combines two parents' genes.
Pollination, Pollination is the transfer of pollen grains from the anther to the stigma, either of the same flower (self-pollination) or of a different flower on a different plant of the same species (cross-pollination); the transfer is carried out by an external agent such as wind or an insect, and floral features often reveal which agent a flower relies on. A flower can receive its own pollen and pollen from another plant at the same time, so both types of pollination are not always mutually exclusive events.
Fertilisation, After pollination, a pollen tube grows down through the style towards the ovule, carrying two male gametes; in double fertilisation, one male gamete fuses with the female gamete to form a diploid zygote and the other fuses with two nuclei in the embryo sac to form a triploid tissue called the endosperm, which stores food for the developing embryo. Because two separate fusions occur from the same pollen tube, double fertilisation is unique to flowering plants and is not seen in animals or in non-flowering plants such as ferns.
Seeds and fruits, After fertilisation, the ovule develops into a seed containing the embryo, its food store and a protective seed coat, while the ovary wall develops into the fruit, which protects the seed or seeds inside and, in many species, also assists with dispersal.

Frequently asked questions

What is the difference between pollination and fertilisation?

Pollination is the transfer of pollen grains from the anther to the stigma, either within the same flower (self-pollination) or between different plants of the same species (cross-pollination). Fertilisation happens afterwards: a pollen tube grows down to the ovule and the male gamete fuses with the female gamete to form a zygote. Pollination brings the gametes close; fertilisation is their fusion.

What happens to the flower after fertilisation?

After fertilisation, the fertilised ovule develops into a seed, which contains the embryo and a food store. The ovary wall develops into the fruit, which protects the seeds and often helps to disperse them. The other flower parts, such as the petals and stamens, usually wither and fall off. Recognising which structure has become which part after fertilisation is often tested directly by name in a labelling question.

How do wind-pollinated and insect-pollinated flowers differ?

Insect-pollinated flowers are usually large and colourful with scent and nectar to attract insects, and have sticky stigmas and pollen. Wind-pollinated flowers are usually small and dull with no scent, and have feathery stigmas and light, smooth pollen produced in large amounts, so the wind can carry it easily.