Why reproduce?
Every living thing eventually dies. Reproduction is how life continues: organisms make new individuals called offspring. There are two main types: asexual and sexual.
Asexual reproduction
Asexual reproduction needs only one parent. The offspring are genetically identical to the parent; they are clones.
| Type | How it works | Examples |
|---|---|---|
| Binary fission | One cell splits into two | Bacteria, amoebas |
| Budding | A small growth breaks off | Yeast, hydra |
| Fragmentation | A piece breaks off and grows into a whole | Starfish, some worms |
| Spores | Tiny cells grow into new organisms | Mushrooms, ferns |
| Vegetative propagation | New plants grow from roots, stems or leaves | Strawberry runners, potatoes |
Advantages: fast, needs no partner, lots of offspring.
Disadvantages: no variation, so a single disease or environmental change can wipe out the whole population.
Sexual reproduction
Sexual reproduction involves two parents. Each parent makes special sex cells called gametes:
- Male gametes: sperm cells (in plants, carried in pollen)
- Female gametes: egg cells
During fertilization, a sperm and an egg join to form a zygote, which develops into a new organism. Each gamete carries half the genetic information, so the offspring get a mix from both parents.
Advantages: produces genetic variation, which helps populations survive changes.
Disadvantages: slower, uses more energy, needs a partner.
Comparing the two
| Asexual | Sexual | |
|---|---|---|
| Number of parents | One | Two |
| Gametes needed | No | Yes |
| Offspring | Identical to parent | Different from both parents |
| Speed | Fast | Slower |
| Variation | None (except mutations) | High |
Reproduction in flowering plants
- Pollination: pollen moves from the anther (male part) to the stigma (female part). Bees, birds, bats and wind are pollinators.
- A pollen tube grows down to the ovary.
- Fertilization: the male gamete joins the egg inside an ovule.
- The ovule becomes a seed; the ovary becomes a fruit.
- Seeds are dispersed by wind, water or animals.
Many plants can reproduce both ways. Strawberries make seeds but also send out runners.
Reproduction in animals
- External fertilization: eggs and sperm meet outside the body, usually in water (most fish and frogs). Many eggs are released because few survive.
- Internal fertilization: fertilization happens inside the female’s body (mammals, birds, reptiles). Fewer eggs, but better protected.
After fertilization, development may happen:
- in an egg outside the body (birds, most reptiles)
- inside the mother’s body (most mammals)
Human reproduction
In humans, the reproductive system produces gametes and, in females, supports the development of a baby for about nine months. Puberty is the stage when the reproductive system matures, triggered by hormones from the endocrine system.
In the real world
Farmers use cuttings (asexual) to grow identical copies of the best fruit trees. Plant breeders cross different varieties (sexual) to create new varieties with useful traits, like disease resistance.
Common mistakes
- Thinking asexual reproduction only happens in "simple" organisms. Many plants and some animals use it.
- Thinking offspring of sexual reproduction are a perfect 50/50 blend. They inherit a random mix.
Try it yourself
- Place a potato with "eyes" in a jar of water. Watch it sprout. Which type of reproduction is this?
- Make a table comparing a strawberry plant and a dog: how does each reproduce?
- Explain why a field of identical cloned bananas might be at risk from one disease.
Quick recap
- Reproduction makes offspring and continues life.
- Asexual reproduction has one parent and makes identical offspring.
- Sexual reproduction joins two gametes at fertilization and creates variation.
- Flowering plants rely on pollination before fertilization.
- Variation helps populations survive changing environments.