Wednesday, 8 April 2009

iGCSE Biology - Reproduction in Humans

·        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.





Number of cell divisions



Number of cells formed



Number of chromosomes in cells formed



Type of cells formed

Body cells

Sex cells

Genetic variation in cells formed




·        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

In girls

Sperm production starts

The menstrual cycle begins.

Growth and development of male sexual organs.

Growth and development of female sexual organs.

Growth of armpit hair, pubic hair, chest hair, and facial hair.

Growth of armpit hair and pubic hair.

Increase in body mass; growth of muscles, e.g. chest.

Increase in body mass; development of “rounded” shape to hips.

Voice breaks

Voice deepens

Sexual “drive” develops

Sexual “drive” develops

Breasts develop

My notes only go up to here: everything else is in the textbook.

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