Reproduction, and asexual reproduction by fission, budding and spores
Reproduction is how living things produce their own kind, so the species goes on. In asexual reproduction, a single parent forms young ones by fission, budding or spores.
What reproduction is and why it matters
Every family continues from one generation to the next, and every living thing produces its own kind. This process is reproduction. No living thing lives for ever, so without reproduction a species would die out. A species is a group of living things that can breed with each other, look alike and share the same kind of genes. All human beings, wherever they live, belong to one species, Homo sapiens. No living thing can reproduce soon after birth: it must first grow and become mature.
Asexual vs sexual reproduction
Some animals, such as sponges and Hydra, can reproduce both asexually and sexually.
Asexual reproduction in simple organisms
| Method | What happens | Examples |
|---|---|---|
| Binary fission | One cell divides into two new individuals and so loses its own identity | Amoeba, bacteria |
| Budding (in a single cell) | A small bud grows out of the parent cell. The parent nucleus stretches and divides, and one part moves into the bud | Yeast |
| Budding (in a many-celled animal) | A bud grows from the body, forms all its parts, and then separates from the parent | Hydra, sponges |
| Spore formation | The nucleus and cytoplasm divide again and again to form spores, single cells that grow into new individuals once released | Chlamydomonas (4 to 8 spores), fungi, mosses, ferns |
How to draw binary fission, budding and spore formation
- 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 Amoebae.
- Yeast: draw an oval cell with a small round bud on its side, and a nucleus in each. Add a short chain of buds if you like.
- Hydra: draw a tube-shaped body with tentacles at the top and a small bud on one side. Then show the bud grown, with its own tentacles, separating from the parent.
- Chlamydomonas: draw one cell divided into 4 to 8 small spores, and the spores being set free.
- Label each stage and write a title, such as Binary fission in Amoeba.
Bacteria that turn milk into curd multiply by binary fission, which is why a spoonful of curd can set a whole pot of milk. Yeast, which multiplies by budding, makes bread and pav dough rise.
1 marks: “Name an organism that reproduces by budding.” Yeast (Hydra also reproduces by budding).
2 marks: “Hydra can make young by budding, and also by the fusion of gametes. Give two differences between these two ways of reproducing.” Budding is asexual: one parent; no gametes fuse; the young are copies of the parent. Fusion of gametes is sexual: two parents; a male and a female gamete fuse; the young show more variety.
2 marks: “When an Amoeba splits into two, why do we call it asexual reproduction?” Only one parent cell is involved. It divides into two daughter cells and loses its own identity, and no gametes fuse.
Simple organisms split, sprout or scatter: fission (split), budding (sprout), spores (scatter).