Living things are able to reproduce themselves. If organisms fail to do this, populations will diminish and disappear as their members die from old age, disease, accidents, predation, etc. It is a fundamental law of biology that living things can only be produced by other living things; every living organism owes its existence to the reproductive activities of other organisms.
This is contrary to the misconceived ideas of spontaneous generation which some people held in the past. The notion that cockroaches were formed out of crumbs on the bakery floor, that mould was formed out of decaying bread and that rotting sacks of grain turned into mice are examples of how spontaneous generation was thought to operate. Today, these ideas are discredited but they still often provide the stimulus for works of dramatic fiction!
There are two fundamental types of reproduction:
|Asexual reproduction||Asexual reproduction involves no exchange of genetic material but is a simple replication to produce a new organism. Organisms produced in this way display little or no genetic variation from the parent organism and are called clones. Plants growing from tubers or bulbs such as potatoes and daffodils are displaying asexual reproduction.|
|Sexual reproduction||Sexual reproduction involves the combining of genetic material from two parent organisms. The offspring from sexual reproduction will generally display some of the characteristics of both parents. Sexual reproduction ensures that there is high degree of variation within populations. The parent organisms give rise to reproductive cells called gametes. These are formed by a special type of cell division called meiosis. The cells produced in this way has half the normal amount of genetic material. When the gamete from one parent fuses with the gamete of the other, the resulting single cell (called a zygote) has a full complement of genetic material, half coming from one parent and half from the other.|