Stem cells: Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

The idea

Cloning crop plants allows farmers to obtain many genetically identical plants that all carry a desirable feature, such as disease resistance. A common method is taking cuttings: a piece of stem or leaf is removed from the parent plant and grown into a new plant. Another method is tissue culture, where small groups of cells are grown on a sterile nutrient medium to produce many plantlets. Because the offspring are clones, they inherit the same alleles for disease resistance as the parent. This gives uniform, predictable crops and can increase yield. However, genetic uniformity means that if a new disease or pest can overcome the resistance, the whole crop may be lost. Farmers may also need to manage soil nutrients and pests carefully because all plants have the same requirements.

What earns the marks

• Cloning produces genetically identical offspring, so desirable features such as disease resistance are passed on unchanged.
• Cuttings involve taking a section of stem or leaf from a parent plant and growing it into a new plant.
• Tissue culture uses small groups of plant cells grown on a sterile nutrient medium to produce many identical plantlets.
• Large numbers of identical plants can be produced quickly for farmers, giving uniform crops and predictable yields.
• A risk of genetic uniformity is that a new disease or pest could affect all plants because they share the same resistance alleles.
• Cloning is useful when a plant has a special feature, but farmers still need to manage the environment and pests.

Common mistakes and how to put them right

• Thinking tissue culture produces genetically different plants.

  Put it right: Tissue culture produces clones, so the plants are genetically identical to the parent.

• Confusing cuttings with seed production.

  Put it right: Cuttings are a form of asexual reproduction and do not involve fertilisation or seed formation.

• Ignoring the risk of uniform crops.

  Put it right: If all plants are identical, a single disease or pest may destroy the whole crop.

Exam tips

• Name the cloning method clearly, such as cuttings or tissue culture, and state that the offspring are genetically identical.
• Link the special feature to the farmer's benefit: disease resistance means fewer plants are lost, so yield is more reliable.
• For evaluation questions, give both an advantage and a disadvantage of cloning crop plants, such as uniform yield but vulnerability to disease.