Sexual reproduction in plants — Eduqas A-Level Biology

Sexual reproduction in plants involves the fusion of male and female gametes to produce genetically diverse offspring. In flowering plants (angiosperms), the process begins with pollination, where pollen grains (male gametophytes) are transferred from the anther to the stigma. This is followed by fertilisation, where the male gamete fuses with the female gamete inside the ovule, leading to seed and fruit development. Key structures include the flower, which contains the male reproductive organs (stamens: anther and filament) and female reproductive organs (carpel: stigma, style, ovary). Understanding this process is crucial for grasping plant life cycles, genetic variation, and agricultural practices such as crop breeding.

The topic also covers the adaptations of flowers for different pollination methods—wind and insect pollination. Wind-pollinated flowers (e.g., grasses) produce large quantities of lightweight pollen and have feathery stigmas to capture it. Insect-pollinated flowers (e.g., buttercups) have brightly coloured petals, scent, nectar, and sticky pollen to attract insects. After fertilisation, the ovule develops into a seed, and the ovary develops into a fruit. Seeds contain an embryo and a food store, and are dispersed by various mechanisms (wind, animals, water, explosion) to colonise new areas. This topic is fundamental to understanding plant reproduction, evolution, and ecosystem dynamics.

In the WJEC A-Level Biology specification, this topic is part of the 'Plant Biology' module. It builds on GCSE knowledge of plant structure and introduces detailed processes such as double fertilisation in angiosperms, where one sperm fuses with the egg to form a zygote, and another fuses with polar nuclei to form endosperm. Students must also understand the role of hormones like auxin in fruit development. Mastery of this topic is essential for higher-level concepts in genetics, ecology, and biotechnology, and it frequently appears in exam questions requiring labelled diagrams and explanations of adaptations.

• →Structure of a flower: sepals, petals, stamens (anther and filament), carpel (stigma, style, ovary containing ovules).
• →Pollination: transfer of pollen from anther to stigma; types include self-pollination and cross-pollination, with cross-pollination promoting genetic diversity.
• →Double fertilisation: one sperm nucleus fuses with the egg cell to form a diploid zygote; the other fuses with two polar nuclei to form a triploid endosperm nucleus.
• →Seed and fruit development: after fertilisation, the ovule becomes a seed (containing embryo, endosperm, and seed coat), and the ovary becomes a fruit.
• →Adaptations for pollination: wind-pollinated flowers have exposed anthers, feathery stigmas, and large amounts of lightweight pollen; insect-pollinated flowers have colourful petals, scent, nectar, and sticky pollen.

• Comparison of wind and insect-pollinated flower structures
• Development of pollen and ovules
• Distinction between cross and self-pollination
• Process of double fertilisation
• Formation and structure of seed and fruit (broad bean and maize)
• Process of germination in Vicia faba
• Effect of gibberellin on germination

• 💡Ensure you can distinguish between the structural adaptations of wind-pollinated versus insect-pollinated flowers.
• 💡Be prepared to interpret and draw from prepared slides of anthers and ovaries.
• 💡Understand the specific role of gibberellin in breaking seed dormancy.
• 💡Always label diagrams of flower structures clearly, including the anther, filament, stigma, style, ovary, and ovule. Use correct spelling—'carpel' not 'carpal'.
• 💡When explaining double fertilisation, specify that one sperm nucleus fuses with the egg to form a diploid zygote, and the other fuses with two polar nuclei to form a triploid endosperm nucleus. Mention that the endosperm provides nutrition for the developing embryo.
• 💡For adaptation questions, compare wind- and insect-pollinated flowers using specific features (e.g., 'wind-pollinated flowers have feathery stigmas to catch pollen from the air'). Avoid vague statements like 'they are adapted' without details.

• Misconception: Pollination and fertilisation are the same process. Correction: Pollination is the transfer of pollen to the stigma; fertilisation is the fusion of gametes after pollen tube growth.
• Misconception: All flowers have both male and female parts. Correction: Some flowers are unisexual (e.g., male or female only), and plants may be monoecious (both sexes on same plant) or dioecious (separate plants).
• Misconception: The fruit is always sweet and fleshy. Correction: Fruits can be dry (e.g., nuts, achenes) or fleshy (e.g., berries, drupes); they all develop from the ovary after fertilisation.