All living things need to make more copies of themselves. Inside each living cell is a chemical called Deoxyribonucleic Acid (or DNA for short). It controls what an organism looks like and how it behaves: it's a bit like a computer program. When living cells reproduce they need to make more copies of this DNA code - and that controls the development of a new organism.
Two Types of Reproduction
Organisms can reproduce their cells in two ways: by sexual reproduction and by asexual reproduction. Many organisms use both types of reproduction to create more cells in their bodies and to make children.
|Sexual Reproduction||Asexual Reproduction|
|needs two organisms of the same species||only needs one organism|
|child is different to the parents||child is an exact copy of the parent|
|special cells called gametes are created||no special cells involved|
Asexual Reproduction and Cell Division
This is a very simple way for a cell to reproduce. It simply splits its DNA into two exact copies and then splits the rest of its cell into two. Many multicellular organisms (made out of lots of cells) use this sort of reproduction for growth and repair. For example, you are probably bigger than you were when you were born. Most of your cells haven't got bigger - you just have more of them. And they divided asexually.
Some plants and animals are able to make new organisms by asexual reproduction.
Many bacteria, plants and animals that are made of only one cell are able to make a child by either dividing into two (binary fission) or by growing a mini version of themselves (budding) which drops off when it's ready. Rarely, some female animals are able to produce eggs that have enough DNA in them and don't need to be fertilised (parthenogenesis) so they hatch into new females without the need for a male.
For sexual reproduction to occur there must be two parents of the same species. When sexual reproduction happens the DNAs from both parents need to combine together to make the child. Different species have different amounts of DNA so they can't combine properly to make a new organism.
Another important thing about sexual reproduction is the fact that the child needs to have exactly the same amount of DNA as its parents. If the parents just joined cells then the child would end up with twice as much DNA as it should have. So the parents need to make special sex cells or gametes. These are often called sperm and eggs in animals and pollen and egg cells in flowering plants. These gametes have half the amount of DNA as the parents - so that, when they join together, the child has the same amount of DNA as the parent.
The joining together of the two gametes is called fertilisation. Plants and animals have evolved many different ways in which this can occur. Flowering plants produce pollen which is carried to other plants by insects, wind, birds, etc. during pollination . Mammals bring their sperm and eggs together during sexual intercourse; fish use the water to enable their sperm to swim to the eggs. Ferns are strange plants which are able to produce sperm which swims to another plant in rain water.