There are two types of reproduction: sexual reproduction and asexual
reproduction.

Sexual reproduction:
Specialised sex cells called gametes are produced.
The male gamete (sperm) is mobile and the female gamete (ovum) is
stationary.
The sperm moves to the ovum and fertilises it.
The single cell formed by fertilisation is called a zygote.

Asexual reproduction:
There are no gametes and no fertilisation.
Cells undergo mitosis and a structure which breaks away from the main
body is formed.
This structure grows into a new creature.

All offspring produced by asexual reproduction are genetically identical.

Sperm are produced in the testes and ova are produced in the ovaries.

These gametes are produced by meiosis, and thus have only half the number
of chromosomes, making them haploid cells.
Feature
Number of cell divisions
Number of cells formed
Number of chromosomes in cells formed
Type of cells formed
Genetic variation in cells formed
Mitosis
1
2
Diploid
Body cells
None
Meiosis
2
4
Haploid
Sex cells
Variation

Sperm have a tail (flagellum) which makes them specialised for swimming.

Some animals reproduce through external fertilisation in which the males
and females release their gametes into the water.

Most animals reproduce through internal fertilisation, in which the male
ejaculates his sperm into the bodies of the females.

As each gamete has half the number of chromosomes, the zygote will have
the full number.

The zygote grows through mitosis.

Human sexual reproduction:
1.
Sperm are produced in the testes by meiosis.
2. During sexual intercourse they pass down the sperm duct and are
mixed with fluid from the seminal vesicles to produce semen.
3. The semen is ejaculated into the woman’s vagina and travels towards
the fallopian tubes.
4. One ovum is released every month into a Fallopian tube, at which point
it may be fertilised by sperm.
5. The zygote will develop into an embryo and implant itself in the lining
of the uterus.
6. The embryo then develops a placenta which allows the embryo to
receive materials such as food and oxygen from its mother.
7. The amnion develops around the embryo, and it secreted amniotic
fluid, which acts as a shock absorber for the embryo.
8. When the embryo becomes recognisably human we call it a foetus,

Childbirth:
1.
Cervix dilates.
2. Uterus contracts to burst the amnion.
3. Uterus contracts to deliver the baby.
4. After birth, the uterus continues to contract to deliver the placenta.

Presence of sexual organs is called primary sexual characteristic.

During puberty, secondary sexual characteristics become apparent.

Testosterone causes male secondary sexual characteristics and oestrogen
causes female secondary sexual characteristics.
In boys
Sperm production starts
Growth and development of male
sexual organs.
Growth of armpit hair, pubic hair,
chest hair, and facial hair.
Increase in body mass; growth of
muscles, e.g. chest.
Voice breaks
Sexual “drive” develops
In girls
The menstrual cycle begins.
Growth and development of female
sexual organs.
Growth of armpit hair and pubic hair.
Increase in body mass; development
of “rounded” shape to hips.
Voice deepens
Sexual “drive” develops
Breasts develop