Stem cells: Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.

The idea

In plants, stem cells are found in meristems, such as the tips of roots and shoots. These cells can divide and differentiate into any plant cell type. A small piece of meristem tissue can be grown in sterile conditions on a nutrient medium, where it forms many genetically identical plantlets. Because one parent plant supplies all the cells, the offspring are clones. This method is quick, because many plantlets form at once, and economical, because only a small amount of parent tissue is needed and the plants can be grown in controlled conditions. It is used to produce large numbers of identical crop plants with useful features, such as disease resistance.

What earns the marks

• State that meristems are regions of unspecialised stem cells in plants, found at root and shoot tips.
• Describe how meristem cells can divide and differentiate to form new plantlets.
• Explain that the new plants are clones because they are genetically identical to the parent plant.
• Explain that the method is quick because many plantlets can be produced at the same time.
• Explain that the method is economical because only a small amount of parent tissue is needed and conditions can be controlled.
• Give a use, such as producing large numbers of identical crop plants with desirable characteristics.

Common mistakes and how to put them right

• Saying meristem cells are specialised.

  Put it right: Meristem cells are unspecialised stem cells that can differentiate.

• Confusing clones with offspring from sexual reproduction.

  Put it right: Clones are genetically identical because no gamete fusion occurs.

• Stating the method is slow.

  Put it right: Tissue culture can produce many plantlets quickly from a small sample.

Exam tips

• Name the meristem as the source of plant stem cells.
• Use the words 'genetically identical' when explaining why the plantlets are clones.
• Link 'quickly' to many plantlets forming at once and 'economically' to using little parent tissue.