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biology 0610printed 208 · PDF 208
328 pagesrevision 46933
printed 208 · PDF 208
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● In a human cell there are two sets of chromosomes. One from the father and
one from the mother. Each set contains 23 chromosomes so in total there are
46 chromosomes in a human cell. A cell that has two sets of chromosomes is
called a diploid.
● A cell containing only one set of chromosomes is called a haploid. Examples
of haploid are gametes.
● Gametes are made when cells inside reproductive organs divide.
● Normally when a cell divides it divides by a process called mitosis in which
new cells contain exactly the same number and type of chromosomes and
genes as the parent cell.
● However when gametes need to be formed with only one set of chromosomes
then cells divide by a process called meiosis. It produces haploid cells from
diploid parent cells.
● Normally one organism can produce only one type of gamete. So they are
either male or female. Some organisms can produce both types of gametes
and these organisms are said to be hermaphrodite.
Flowers
● The function of a flower is to make gametes and to make sure that
fertilization will take place.
● Most flowers are hermaphrodites.
● On the outside of the flower are the sepals. They protect the flower when it is
a bud and they are usually green.
● Inside the sepals are the petals. These are often brightly coloured. They
attract insects to the flowers.
● The female part of the flower is in the centre. It consists of one or more
carpels. A carpel contains an ovary. Inside the ovary are many ovules.
These contain the female gametes.
● At the top of the ovary is the style with a stigma at the tip. The function of the
stigma is to catch the pollen grains.
● The male gametes are inside the pollen grains which are made in the
anthers.