Asexual reproduction in single organisms
In asexual reproduction, one parent gives rise to new individuals by fission, fragmentation, regeneration, budding, vegetative propagation or spores.
Modes of asexual reproduction
| Mode | What happens | Examples |
|---|---|---|
| Fission | A single cell divides into two (binary fission) or many (multiple fission) | Amoeba, Leishmania (binary); Plasmodium (multiple) |
| Fragmentation | The body breaks into pieces when mature; each piece grows into a new individual | Spirogyra (a green alga) |
| Regeneration | A cut piece grows into a whole organism, using specialised cells that divide and form all the tissues | Hydra, Planaria |
| Budding | An outgrowth (bud) forms by repeated cell division at one spot, grows, and detaches when mature | Hydra, yeast |
| Vegetative propagation | New plants grow from a root, stem or leaf | Bryophyllum (leaf buds), potato, sugarcane, rose, grapes, banana |
| Spore formation | Upright stalks on thread-like hyphae carry round sporangia full of spores; spores grow on a moist surface | Rhizopus (bread mould) |
Binary fission vs multiple fission
Activity: binary fission in Amoeba and budding in yeast and Hydra
- 1Look at a prepared slide of Amoeba showing binary fission under a microscope.
- 2★Observe: the nucleus divides first, then the cytoplasm pinches in the middle, giving two daughter Amoebae.
- 3For yeast, dissolve about 10 g of sugar in 100 mL of water, add a pinch of yeast to some of it in a test tube, plug it with cotton and keep it warm for 1 to 2 hours. (A prepared slide can also be used.)
- 4★Put a drop of the yeast culture on a slide, cover it and observe: small buds grow out of the yeast cells, and some buds form short chains.
- 5Look at a prepared slide of Hydra: a small bud grows from the side of the body, forms its own tentacles, and later detaches as a new Hydra.
★ key step
Vegetative propagation and its benefits
In vegetative propagation, a new plant grows from a root, stem or leaf instead of a seed. In Bryophyllum, buds form in the notches along the leaf edge, fall on the soil, and grow into new plants. Farmers use layering and grafting to grow sugarcane, roses and grapes. Plants raised this way flower and fruit earlier than plants grown from seed. The method also lets us grow plants that have lost the ability to make seeds, such as banana, orange, rose and jasmine, and the new plants are genetically similar to the parent.
How to draw binary fission in Amoeba and budding in Hydra
- Amoeba: draw four stages from left to right. (1) One Amoeba with a nucleus. (2) The nucleus divides into two. (3) The cytoplasm pinches in the middle. (4) Two daughter cells.
- Hydra: draw a tube-shaped body with tentacles at the top and a small bud on one side.
- Draw the next stages: the bud grows, forms its own tentacles, and separates from the parent.
- Rhizopus, if asked: draw thread-like hyphae with upright stalks carrying round sporangia full of spores.
- Label each stage and write a title, such as Binary fission in Amoeba.
Gardeners grow new rose and money plant plants from stem cuttings, and farmers plant sugarcane from pieces of stem. The fuzzy black growth on stale bread or roti is Rhizopus growing from spores.
2 marks: “How does Plasmodium reproduce? How is this different from reproduction in Amoeba?” By multiple fission: one cell divides into many daughter cells at once. Amoeba divides into only two by binary fission.
3 marks: “What is vegetative propagation? Give two advantages and two examples.” Growing new plants from a root, stem or leaf. Earlier flowering and fruiting; grows seedless plants; offspring like the parent. Examples: Bryophyllum, banana, rose, sugarcane.
3 marks: “Draw labelled diagrams to show budding in Hydra.” Parent Hydra with tentacles and a small bud; bud growing with its own tentacles; bud separating as a new Hydra; all stages labelled.
Six asexual modes: Fat Frogs Rarely Bounce Very Slowly: Fission, Fragmentation, Regeneration, Budding, Vegetative propagation, Spores.