Edexcel IGCSE Biology · Spec 3.7
Asexual Reproduction in Plants
Natural and artificial asexual reproduction in plants, including growing new plants from cuttings.
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Asexual Reproduction in Plants
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Explained
Plants that copy themselves
Asexual reproduction involves one parent, no gametes and no fertilisation. The offspring are produced by mitosis, so they are genetically identical to the parent and to each other. They are clones.
Plants do this far more readily than animals, and they do it both naturally and with a good deal of help from gardeners.
Runners
A runner is a horizontal stem that grows out sideways from the parent plant, along the surface of the soil. At intervals it produces a plantlet, which grows its own roots where it touches the ground.
Once the new plant is established, the runner connecting it to the parent withers, and the plantlet is independent. Strawberry plants and spider plants both do this, which is why one plant becomes a patch.
Cuttings
A gardener cuts a short length of stem, usually with a few leaves on it, and plants it. It grows roots and becomes a new plant identical to the one it came from.
Several steps improve the chances. Dipping the cut end in rooting powder, which contains plant hormones, encourages roots to form. Removing most of the leaves reduces water loss by transpiration before there are roots to replace it. Covering the cutting with a plastic bag keeps the air humid, which does the same thing. And keeping it warm speeds up growth.
Each of those has a reason attached, and the reason is what the marks are for.
The advantages and the risk
Asexual reproduction is fast, needs no pollinator or mate, and produces offspring identical to a parent whose characteristics you already know are good. A grower who has a plant with the right flavour or the right disease resistance can produce thousands more exactly like it.
The risk is the same identity. Because there is no genetic variation, if a new disease can infect one plant it can infect all of them, and the whole crop can be lost. And if conditions change, the population has nothing to select from and cannot adapt.
What the mark scheme accepts and rejects
An Edexcel International GCSE Biology mark scheme asks for differences between asexual and sexual reproduction and lists four: asexual produces genetically identical offspring or clones, asexual has no fertilisation and no gametes, asexual has only one parent cell, and asexual uses only mitosis rather than meiosis or haploid cells.
Its guidance accepts the converse for all of these, accepts that the offspring have the same genes, alleles or DNA, and accepts that asexual reproduction does not produce a zygote. Then it says to ignore one parent alone and to ignore no need for a mate.
Both of those are true statements, and neither is precise enough. The mark scheme wants one parent cell, not one parent, which is the same distinction the reports draw when they say candidates should refer to two parent cells rather than two parents in sexual reproduction.
Elsewhere the same mark scheme credits mitosis for asexual reproduction, producing genetically identical offspring or cells, and producing clones, as three separate points. The process, the outcome and the name for the outcome are each worth a mark, so give all three.
Other natural methods
Bulbs, such as daffodils and onions, contain a food store and produce new bulbs alongside the parent. Tubers, such as potatoes, are swollen underground stems that each sprout into a new plant. A potato grown from a tuber is a clone; a potato grown from a seed is not.
That distinction is a favourite question, because the same plant reproduces both ways and only one of them produces variation.
Spec 3.7
What you need to know
- Recall that asexual reproduction makes identical clones
- Describe how plants reproduce naturally using runners
- Describe how gardeners use cuttings
Active recall
Quick check
Answer each question before opening the answer.
Give an example of natural asexual reproduction in plants.
Runners (e.g. strawberry), bulbs or tubers producing genetically identical new plants.
What is a clone?
An offspring that is genetically identical to its parent.
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