IGCSE Biology / Reproduction in humans
Runners, tubers and cuttings
Edexcel International GCSE Biology (4BI1), chapter 9: Reproduction in humans, specification point 3.1, 3.7. Free lesson.
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Asexual reproduction makes new plants from one parent, without gametes, so the offspring are genetically identical clones. Plants can reproduce this way naturally or by taking cuttings, and the lack of variation can be both useful and risky.
How plants reproduce asexually
In asexual reproduction, one parent makes offspring without gametes or fertilisation. New plants grow from the parent’s own cells by mitosis, so they are genetically identical to the parent and to each other. These identical offspring are called clones. Runners are horizontal stems that grow along the ground. A new plant forms where a runner touches the ground and puts out roots. Tubers are swollen underground stems that store starch. Each tuber can grow into a new plant. Bulbs store food in swollen leaf bases. New bulbs form beside the parent bulb.
How asexual and sexual reproduction differ
Asexual reproduction is usually fast because it does not require a partner or pollinator. Sexual reproduction involves two parents and two gametes that fuse at fertilisation. Meiosis makes the gametes, producing offspring that are genetically different from both parents and from each other. Asexual: one parent, no gametes, mitosis only, genetically identical offspring. Sexual: two parents, two gametes fuse, meiosis makes the gametes, genetically different offspring. Asexual reproduction can quickly copy a successful plant. However, clones have no genetic variation, so a disease or change in…
How to take a cutting
A cutting is an artificial way to make a clone. Because it has no roots at first, it cannot replace water lost from its leaves. Each step reduces water loss or encourages roots to grow.
Why growers use cuttings
Taking cuttings uses the same process as natural asexual reproduction: new plants grow from a parent’s cells by mitosis. The resulting plants are clones, which lets a grower produce many identical plants from one good specimen. A successful plant can be copied exactly. Because the offspring are clones, they share the same vulnerability to a new disease or changing conditions.