By the end of this lesson
- Describe natural vegetative reproduction.
- Explain artificial propagation by cuttings.
- Evaluate benefits and risks of cloning crops.
BIG QUESTION
How can one plant become many without producing seeds?
Vegetative tissues can form new roots and shoots because many plant cells retain developmental potential.
Vegetative structures spread naturally
Plants may reproduce from runners, bulbs, tubers or rhizomes. New shoots and roots arise by mitosis from vegetative tissues.
Strawberry runners and potato tubers are examples; the offspring are clones of the parent plant.
Growers propagate useful genotypes
A cuttingA piece of stem or leaf removed from a plant and grown into a new, genetically identical plant. is a piece of stem or leaf encouraged to form roots and shoots under moist conditions. Rooting hormone may increase success.
Tissue culture can generate many disease-screened plantlets from a small explant under sterile conditions.
Uniformity is useful but risky
Cloning preserves desirable traits, gives a predictable crop and can multiply plants that make few viable seeds.
Low genetic variation means a pathogen or environmental stress may affect many plants similarly.
Asexual propagation methods
All avoid gamete fusion but use different plant structures.
| Method | Starting structure | Use/feature |
|---|---|---|
| Runner | Horizontal stem. | Plantlets form at nodes. |
| Tuber | Swollen underground stem. | Buds grow into shoots. |
| Bulb | Short stem and fleshy leaves. | Offsets form new plants. |
| Cutting | Removed stem/leaf piece. | Roots and shoots are induced. |
| Tissue culture | Small sterile explant. | Rapid large-scale multiplication. |
Language that earns precision
- vegetative reproduction
- Asexual reproduction using non-reproductive plant tissues.
- cutting
- Plant piece induced to develop into a new individual.
- explant
- Small piece of plant tissue used to start tissue culture.
- runner
- Horizontal stem producing new plantlets at nodes.
Common misconceptions
Claim: A potato tuber is a root.
Correction: It is a modified underground stem with buds or eyes.
Claim: Every plant made from a cutting is mutation-free.
Correction: It is a clone initially, but mutations can still occur.
Claim: Cloning is always preferable in farming.
Correction: Uniformity improves predictability but reduces genetic resilience.
Match the answer to the command word
Name the structure and explain how a new plant forms.
Balance rapid uniform production against shared susceptibility.
Recall, apply, then justify
Describe how a stem cutting can produce a new plant.
Hint
Select tissue, reduce water loss, root, then grow.
Suggested marking points
- A healthy stem section with a node is removed.
- Lower leaves are removed and water loss is limited.
- The base is placed in moist growth medium, optionally with rooting hormone.
- Roots and shoots develop by mitotic growth.
Explain one benefit and one risk of cloning crop plants.
Hint
Preserved genotype versus low variation.
Suggested marking points
- A desirable genotype is preserved in all offspring.
- This gives a uniform predictable crop or rapid multiplication.
- The plants have little genetic variation.
- A disease or environmental change may therefore damage many plants similarly.
Design a fair comparison of rooting success with and without rooting hormone.
Planning hint
Replication, randomisation, constants and a measurable outcome.
What a strong design includes
- Take many similar cuttings from the same parent or matched parents.
- Randomly assign cuttings to hormone and control groups.
- Use the same solvent/application without hormone for the control group.
- Keep cutting size, leaf area, medium, water, light, temperature and time constant.
- Use several replicates in each treatment.
- Measure proportion rooted, root number or mean root length using a fixed criterion.
- Compare group means or proportions and note natural variation.