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How plants and animals reproduce
Learn the different ways plants and animals reproduce.
Many plants can grow from a part of themselves (a leaf, stem or root) planted in soil. This is vegetative propagation, and it is how bamboo and sugarcane spread without anyone ever seeing their seeds.
Try it (Activity 13.3). Take a stem cutting of a money plant, the 'eyes' of a sprouted potato, or a piece of ginger. Plant each separately in moist soil, not too deep (a money plant is easy to watch in a glass of water). Give them water, air and sunlight, look every day, and note how many days the roots, stem and leaves take to appear, and when the first new leaf comes.
Microbes and simple animals reproduce from one parent too:
| Organism | How |
|---|---|
| bacteria, amoeba | split into two identical individuals |
| algae | regrow from cut pieces |
| hydra | grows buds that break off |
| planaria (a flatworm) | regrows from a piece of its body |
In sexual reproduction there are two parents, usually called male and female. It is easy to see in animals, but flowering plants have male and female parts too, and even bacteria and yeast have two 'mating types' that act like two parents.
If both parents passed on all their genetic material, wouldn't the young end up with double the instructions, doubling again every generation? No. Each parent makes special reproductive cells called gametes, which carry only half of that parent's genetic material. When a male and a female gamete join, they form a new cell with one complete set: half from each parent.
In plants, the pollen grains inside a flower's anther are the male gametes, and the ovules deep inside the flower are the female gametes. Wind, insects or animals carry pollen to another flower: pollination. When the male and female gametes join, that's fertilisation. It forms a zygote, which becomes the seed, while the fleshy part around the ovule grows into a fruit.
When birds or animals eat the fruit, they often drop the seeds far from the parent plant, a handy way for plants to spread. That's how a banyan seed, dropped by a bird that ate the fruit, can sprout in a crack in a wall after the rains. Given water, a seed uses its stored food to grow roots and shoots.
In animals the gametes are sperm (male) and eggs (female).
| Animals | Where fertilisation happens | Where the young develop |
|---|---|---|
| fish, frogs | sperm and eggs are released into the water and join there | the embryo develops in the water too |
| birds | inside the female's body | she lays the egg; the embryo develops during hatching, living on the food she packed into it |
| most mammals, including humans | inside the female's body | inside the mother, whose body supplies all its food and oxygen until birth |
An egg is like a packed lunch that must last until hatching. A mammal's baby is fed from inside the mother the whole time, which is also safer: eggs left outside are often eaten.
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