Micropropagation (tissue culture): the method
Micropropagation (also called tissue culture) is a way of making very large numbers of identical plants from one parent plant. Small pieces of tissue called explants are grown in vitro — that is, in glassware in the laboratory rather than in soil.
Why it works
Plants contain meristem tissue (at shoot tips and root tips) whose cells are still able to divide and to differentiate into any plant cell type. A tiny piece of this tissue can therefore regenerate a whole plant.
The stages — learn these in order
- Select a parent plant with the desirable characteristics you want to copy.
- Cut small explants from the plant, usually from the fast-growing shoot tip (meristem).
- Sterilise the explants, e.g. by dipping in dilute bleach or alcohol, to kill bacteria and fungi that would otherwise compete with the tissue and destroy it.
- Transfer each explant to a sterile nutrient agar (growth) medium. The medium contains glucose (for respiration, because the explant cannot yet photosynthesise enough), amino acids, minerals and plant hormones (auxins and cytokinins) to stimulate cell division, shoot growth and root growth.
- Keep the containers in aseptic conditions in a warm, controlled environment with suitable light.
- The cells divide by mitosis to form a shapeless mass of cells called a callus, which then differentiates into small plantlets with shoots and roots.
- Transplant the plantlets into compost/greenhouse conditions and grow them on. All of them are clones — genetically identical to the parent plant and to each other.
Key vocabulary you must actually write
- explant (not "bit of plant")
- in vitro
- sterile / aseptic
- nutrient medium containing hormones
- mitosis
- clones / genetically identical
Common mistake
Writing that the cells divide by meiosis. Meiosis halves the chromosome number and produces genetic variation — the exact opposite of what cloning needs. Cloning of any kind is always mitosis.
Examiner tip. Two marks are routinely thrown away here. (1) Examiners repeatedly report candidates saying cell division is meiosis — it is mitosis, because the plants must be genetically identical. (2) If the command word is describe, give the sequence of steps; if it is explain, you must give reasons (e.g. why the explant is sterilised, why hormones are added). Reports say 'describe' and 'explain' are the most commonly confused command words.