By the end of this lesson
- Describe the stages of micropropagation.
- Explain why aseptic conditions are needed.
- Explain the roles of nutrients and plant hormones in the medium.
BIG QUESTION
How can one plant become thousands of plants in a laboratory?
Tiny pieces of tissue, each able to grow into a whole plant, are cultured in sterile containers.
Taking explants
Small pieces of tissue called explantA small piece of tissue taken from a plant to be grown into a new plant by micropropagation. are cut from a parent plant, often from shoot tips or buds where cells divide actively.
The explants are sterilisedTreated, by heat or chemicals, to kill all microorganisms., for example in dilute bleach, to kill microorganisms on their surface.
Growing in vitro
The explants are placed in vitroCarried out outside a living organism, in glassware in the laboratory. (in glass or plastic containers) on a sterile agar mediumA jelly containing nutrients, used to grow microorganisms or plant tissue in sterile conditions. containing glucose, mineral ions and plant hormonesChemicals, such as auxin, that control plant growth and development; used to make cuttings root or explants form shoots. (auxins and cytokinins).
Cells divide by mitosisCell division that produces two genetically identical diploid cells, for growth, repair and asexual reproduction.. Different hormone balances stimulate shoots and then roots to develop. Small plants are separated, grown on and transferred to compost.
Aseptic technique
Work is done in asepticFree from unwanted microorganisms; aseptic techniques, such as sterilising equipment, prevent contamination of a culture. conditions: sterilised tools, sterile medium and a clean or laminar-flow cabinet.
Bacteria and fungi grow faster than plant tissue on the nutrient medium. If contamination occurs, the microorganisms may outcompete or kill the explants.
Stages of micropropagation
Link each stage to its reason.
| Stage | What happens | Reason |
|---|---|---|
| Take explants | Small pieces cut from shoot tips. | Actively dividing cells. |
| Sterilise | Explants and tools sterilised. | Prevent microbial contamination. |
| Culture on medium | Agar with nutrients and hormones. | Supplies glucose, minerals and growth signals. |
| Transfer to compost | Plantlets grown on in greenhouse. | Develop into mature plants. |
Language that earns precision
- micropropagation
- Growing many new plants from small tissue samples in sterile laboratory conditions.
- explant
- A small piece of plant tissue used to start a culture.
- in vitro
- In glass or plastic containers, outside the living organism.
- aseptic
- Free from contaminating microorganisms.
Common misconceptions
Claim: Micropropagation uses seeds.
Correction: It uses explants, so it is asexual and seeds are not involved.
Claim: The medium is sterilised to kill the plant cells’ diseases inside.
Correction: Sterile technique prevents microorganisms from the surroundings growing on the medium.
Claim: Cells divide by meiosis in tissue culture.
Correction: Cells divide by mitosis, giving genetically identical cells.
Match the answer to the command word
Explants → sterilise → nutrient agar with hormones → shoots and roots → compost.
Link aseptic conditions to microorganisms competing with or killing explants.
Recall, apply, then justify
Describe how micropropagation is used to grow new plants.
Hint
Four stages.
Suggested marking points
- Small pieces (explants) are cut from the parent plant (e.g. shoot tips).
- Explants are sterilised.
- They are grown on agar / medium containing nutrients and plant hormones.
- Plantlets develop shoots and roots and are transferred to compost.
Explain why micropropagation is carried out in aseptic conditions.
Hint
What else could grow on the medium?
Suggested marking points
- Microorganisms (bacteria / fungi) could grow on the nutrient medium.
- They could compete with / infect / kill the explants.
Explain why the agar medium used in micropropagation contains glucose, mineral ions and plant hormones.
Planning hint
Explants cannot yet photosynthesise well.
What a strong design includes
- Explants have few or no leaves, so cannot photosynthesise enough.
- Glucose supplies energy for respiration and materials for growth.
- Mineral ions such as nitrate are needed to make proteins.
- Magnesium ions are needed for chlorophyll.
- Plant hormones stimulate cell division.
- Hormones control the development of shoots and roots.