Sexual and asexual reproduction, and reproduction in plants — Edexcel International GCSE Science (Double Award)

Revision notes

6 short notes, in the order of the specification. Each one in short:

1. Sexual and asexual reproduction

   Sexual reproduction involves two parents, whose male and female gametes fuse at fertilisation to form a zygote, so the offspring show variation. Asexual reproduction involves only one parent and no gametes. The new cells are made by mitosis, so the offspring are genetically identical to the parent and are called clones, giving very little variation.

2. Insect- and wind-pollinated flowers

   Pollination is the transfer of pollen grains from an anther to a stigma. Insect-pollinated flowers have large, brightly coloured petals, nectaries, anthers and a sticky stigma inside the flower, and sticky or spiky pollen. Wind-pollinated flowers have small dull petals, anthers and large feathery stigmas hanging outside, and large amounts of light, smooth pollen.

3. Fertilisation, seeds and fruits

   Fertilisation in a flowering plant is the fusion of the male gamete nucleus with the egg cell nucleus in an ovule. After pollination, a pollen tube grows from the pollen grain down through the style into an ovule, carrying the male nucleus. The fertilised ovule then develops into a seed, and the ovary develops into a fruit.

4. Germination and food reserves

   Germination is when a seed begins to grow into a seedling. During germination, enzymes break down the food reserves in the seed into soluble molecules: starch to sugars, oils to fatty acids and glycerol, and proteins to amino acids. These are used in respiration and growth until the first leaves can photosynthesise.

5. Practical: conditions for germination

   Practical

   Seeds need water, oxygen for respiration and a suitable temperature to germinate. This practical changes one condition at a time: a control tube has damp cotton wool at room temperature, while other tubes lack water, oxygen (boiled water under oil) or warmth (a refrigerator). All tubes are kept dark, and only the control seeds germinate.

6. Asexual reproduction in plants

   Asexual reproduction in plants produces new plants that are clones, genetically identical to the parent. Strawberry plants reproduce naturally by runners, sideways stems that grow roots and new plantlets. Gardeners use an artificial method, cuttings: a short stem is planted in moist compost, grows roots and becomes a new plant with the parent's useful features.