Reproduction in Plants

The flower is the reproductive organ of angiosperms (flowering plants). Its main parts are arranged in whorls on the receptacle at the end of the pedicel (flower stalk). The essential reproductive organs are the stamens (male) and carpel(s) (female).

Sepals: Leaf-like structures, often green, that protect the flower bud. Petals: Often brightly coloured and scented to attract pollinators. Stamen (male reproductive organ): Consists of an anther (produces pollen grains) and a filament (supports the anther). Carpel/Pistil (female reproductive organ): Consists of a stigma (receives pollen), a style (connects stigma to ovary), and an ovary (contains ovules, each containing an egg cell). Receptacle: The part of the flower stalk where the parts of the flower are attached.

Pollination is the transfer of pollen grains from the anther to the stigma. It can be self-pollination (pollen transferred to the stigma of the same flower or another flower on the same plant) or cross-pollination (pollen transferred to the stigma of a flower on a different plant of the same species). Cross-pollination increases genetic variation. Pollination agents include wind, insects, birds, and other animals.

Wind-pollinated flowers (e.g., grasses): Small, dull petals or absent, no scent or nectar, large feathery stigmas to catch pollen, large quantities of light, smooth pollen, anthers often hang outside the flower. Insect-pollinated flowers (e.g., buttercup): Large, brightly coloured petals, often scented, produce nectar, sticky stigmas, smaller quantities of larger, sticky/spiky pollen, anthers enclosed within the flower.

Fertilisation is the fusion of the male gamete (from the pollen grain) with the female gamete (egg cell) within the ovule. After a pollen grain lands on a compatible stigma, it germinates and grows a pollen tube down through the style to the ovule. The male gametes travel down the pollen tube to fuse with the egg cell, forming a zygote.

After fertilisation, the zygote develops into an embryo. The ovule develops into a seed (containing the embryo and food store, protected by a testa/seed coat). The ovary develops into a fruit (which protects the seeds and aids in their dispersal). The ovary wall becomes the pericarp (fruit wall).

Dispersal is the spreading of seeds and fruits away from the parent plant. This is important to reduce competition for light, water, and nutrients, prevent overcrowding, and allow colonisation of new areas. Methods include wind, water, animals (internal and external), and self-dispersal (explosive mechanisms).

Wind Dispersal: Seeds/fruits are light, often have 'wings' (e.g., sycamore) or 'parachutes' (e.g., dandelion). Animal Dispersal (Internal): Fleshy fruits are eaten by animals, and seeds pass unharmed through the digestive tract (e.g., berries, tomatoes). Animal Dispersal (External): Fruits/seeds have hooks or barbs that attach to animal fur or feathers (e.g., burdock). Water Dispersal: Fruits/seeds are buoyant and float on water (e.g., coconut). Self-Dispersal (Explosion): Fruits burst open, scattering seeds (e.g., pea pods, gorse).