Asexual Plant Reproduction

Asexual reproduction is reproduction that needs only one parent. There are no gametes (sex cells), no pollination and no fertilisation.

Compare this with sexual reproduction, where two gametes (e.g. pollen and an egg cell) join at fertilisation and the offspring are a mix of two parents' genes.

Because asexual reproduction uses just one parent and copies its cells by mitosis, every new plant has exactly the same genes as the parent. Offspring that are genetically identical to their parent are called clones.

	Sexual reproduction	Asexual reproduction
Parents	Two	One
Gametes/fertilisation	Yes	No
Cell division	meiosis then mitosis	mitosis only
Offspring	genetically different (variation)	genetically identical clones

Exam tip. The key idea for spec 3.7 is "one parent → genetically identical clones". If a question asks why the offspring are identical, the answer is asexual reproduction by mitosis (one parent).

Some plants reproduce asexually all by themselves, with no help from a gardener — these are natural methods. The example you must know is the runner.

A runner (also called a stolon) is a long, thin side stem that grows sideways out from the parent plant along the surface of the soil. At a point along the runner, a new little plant (a plantlet) forms. This plantlet grows roots down into the soil and leaves up into the air. Once it is established, the runner connecting it to the parent dies away, leaving a separate new plant.

Two classic examples in the specification:

• Strawberry plants send out runners that root to make new strawberry plants.
• Spider plants (a common houseplant) send out runners with little "spiderettes" on the end that root into new plants.

Because the new plant grew from the parent's own body cells (made by mitosis), it is a genetically identical clone of the parent.

Exam tip. Name the method as a runner and the examples as strawberry and/or spider plant. Saying "a new plant just grows" is not enough — describe the side stem that roots into a new plant.

Humans can also make plants reproduce asexually on purpose — these are artificial methods. The example you must know is the cutting.

Taking a cutting works like this:

1. The gardener cuts off a small piece of a plant — usually a part of the stem with a few leaves.
2. The cut end can be dipped in rooting hormone (rooting powder) to encourage roots to grow.
3. The cutting is planted in moist soil (or put in water).
4. The cutting grows new roots and develops into a whole new plant.

Because the cutting was taken from one parent plant and grows by mitosis, the new plant is a genetically identical clone of the parent.

Why do gardeners and growers like cuttings?

• It is a fast, cheap and reliable way to make many new plants.
• Every new plant is identical to the parent, so if the parent has a desirable feature (e.g. lovely flowers, sweet fruit, disease resistance), all the new plants will have it too.

Exam tip. Note the word artificial — a cutting is done by a person, whereas a runner happens naturally. Questions often ask you to classify a method as natural or artificial.

Whether the method is a runner or a cutting, the new plant always comes from the parent's own body cells. These cells divide by mitosis.

Mitosis produces two genetically identical daughter cells from one cell — each daughter cell has exactly the same genes as the original. So as the new plant grows from these cells, it ends up with exactly the same genes as the parent.

This is why we say the offspring are clones: a clone is an organism that is genetically identical to its parent (and to its "siblings" made the same way).

Contrast this with sexual reproduction, where gametes from two parents join. There the offspring get a mixture of genes from both parents, so they are all slightly different — this is variation. Asexual reproduction produces no genetic variation.

Exam tip. If a question asks why the offspring of asexual reproduction are identical, the marking idea is "produced by mitosis from one parent, so they have identical genes (are clones)".

Asexual reproduction is a brilliant strategy in some situations and a risky one in others. You should be able to give both sides.

Advantages

• Fast. A single parent can make many offspring quickly, without finding a mate.
• No pollinator needed. There is no need for pollination, so the plant does not depend on insects, wind or any other pollinator being present.
• Keeps desirable traits. Because the offspring are identical clones, any good feature of the parent (e.g. tasty fruit, attractive flowers, disease resistance) is passed on to every offspring.

Disadvantages

• No genetic variation. All the offspring are identical, so the population shows no variation. If the environment changes or a new disease appears, none of the plants may be able to cope — the whole population could be wiped out, because what kills one kills them all.

	Advantage / disadvantage
Speed	Advantage — fast, no mate needed
Pollinator	Advantage — none required
Good traits	Advantage — kept in every offspring
Variation	Disadvantage — none, so vulnerable to disease/change

Exam tip. For a 2-mark "advantages and disadvantages" question, give one clear advantage with a reason (e.g. "fast, because no mate or pollinator is needed") and the key disadvantage: no variation, so the population is vulnerable to disease or environmental change.