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biology 0610printed 207 · PDF 207
328 pagesrevision 46933
printed 207 · PDF 207
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207
Notes
● There are two types of reproduction.
Sexual reproduction
Asexual reproduction.
● In reproduction each new organism obtains a set of chromosomes from its
parents or parents.
● Chromosomes are long threads of DNA found in the nucleus of a cell.
● They contain a set of instructions known as genes.
Asexual Reproduction
● Asexual reproduction involves just one parent. Some of the parent cells divide
to produce new cells that contain exactly the same genes as the parent cell.
Hence the new organism is said to be genetically identical to its parent.
● Both plants and some animals can produce asexually.
Sexual Reproduction
● In this kind of reproduction parent organisms produce sex cells called
Gametes.
● Eggs and sperms are examples of sex cells.
● Two of these gametes join and their nuclei fuse together in a process known
as fertilization.
● The new cell formed after fertilization is called a zygote. The zygote divides
again and again and forms into a new organism.
● The zygote contains chromosomes from both its parents and can have a
combination of genes. Therefore the offspring is said to be genetically
different from each other and their parents.
Gametes
● Gametes contain only half as many chromosomes as a normal cell. This is so
when two of them fuse together the zygote formed contains the right number
of chromosomes.
● Female gametes tend to be relatively larger and they do not move. In plants
the female gamete is a nucleus inside an ovule. In animals it is called an egg.
● Male gametes are usually much smaller and they can move. In plants they
are found inside pollen grains. In animals they are called sperms.