Sexual Reproduction in Humans (Cambridge (CIE) IGCSE Biology)
Revision Note
Written by: Phil
Reviewed by: Lára Marie McIvor
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The male reproductive system
Structures of the male reproductive system
The male reproductive system has several key components
The structure and function of these components can be seen in the table below
Structure | Function |
|---|---|
Prostate gland | Produces fluid called semen that provide sperm cells with nutrients |
Sperm duct | Sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation |
Urethra | Tube running down the centre of the penis that can carry out urine or semen, a ring of muscle in the urethra prevents the urine and semen from mixing |
Testis | Contained within a bag of skin (scrotum) and produces sperm (male gamete) and testosterone hormone |
Scrotum | Sac supporting the testes outside the body to ensure that sperm are kept at a temperature slightly lower than body temperature |
Penis | Passes urine out of the body from the bladder and allows semen to pass into the vagina of a woman during sexual intercourse |
The male reproductive system diagram
The male reproductive system
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The female reproductive system
Structures of the female reproductive system
The female reproductive system has several key components
The structure and function of these components can be seen in the table below
Structure | Function |
|---|---|
Oviduct | Connects the ovary to the uterus and is lined with ciliated cells to push the released ovum down it. Fertilisation occurs here |
Ovary | Contains ova (female gametes) which will mature and develop when hormones are released |
Uterus | Muscular bag with a soft lining where the fertilised egg (zygote) will be implanted to develop into a foetus |
Cervix | Ring of muscle at the lower end of the uterus to keep the developing foetus in place during pregnancy |
Vagina | The muscular tube that leads to the inside of the woman's body where the males penis will enter during sexual intercourse and sperm are deposited |
The female reproductive system diagram
The female reproductive system
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Gametes & Fertilisation
What is fertilisation?
Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell)
It occurs in the oviducts
Gametes have adaptations to increase the chances of fertilisation and successful development of an embryo
Fertilisation diagram
The sperm enters the egg cell during fertilisation which usually occurs in the oviduct
Adaptations of Gametes
Human gametes
The human gametes are the egg and the sperm cells
Egg and sperm cell diagram
Comparing sperm and egg cells
Adaptive features of the gametes
The gametes are highly specialised cells with adaptive features designed to maximise the chances of successful reproduction
These adaptive features are compared in the table below
Gamete | Adaptive feature | Function |
|---|---|---|
Sperm | has a flagellum (tail) | allows the sperm to swim towards the egg |
contains enzymes in the head region (acrosome) | to digest a route into the egg for fertilisation | |
contains many mitochondria | to provide energy for movement of the flagellum | |
Egg | cytoplasm contains a store of energy | to provide energy for cell division in the developing zygote after fertilisation |
jelly-like coating that changes after fertilisation | to make an impenetrable barrier after fertilisation to prevent more sperm entering the egg |
Comparison of Male & Female Gametes
Comparative Feature | Sperm | Egg |
|---|---|---|
Size | Very small (45 µm) | Large (0.15 mm) |
Structure | Head region, flagellum, many structural adaptations | Round cell with few structure adaptations, covered in a jelly coating |
Motility | Capable of locomotion | Not capable of locomotion |
Numbers | Produced every day in huge numbers (around 100 million per day) | Thousands of immature eggs in each ovary, but only one is released each month |
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Pregnancy: growth & development of the fetus
After fertilisation in the oviduct, the zygote travels towards the uterus
This takes about 3 days, during which time the zygote will divide several times to form a ball of cells known as an embryo
In the uterus, the embryo embeds itself in the thick lining (implantation) and continues to grow and develop
The gestation period for humans is 9 months
Major development of organs takes place within the first 12 weeks, during which time the embryo gets nutrients from the mother by diffusion through the uterus lining
After this point the organs are all in place, the placenta has formed and the embryo is now called a fetus
The remaining gestation time is used by the fetus to grow bigger in size
The fetus is surrounded by an amniotic sac which contains amniotic fluid (made from the mother’s blood plasma)
This protects the fetus during development by cushioning it from bumps to the mother’s abdomen
The umbilical cord joins the fetus’s blood supply to the placenta for exchange of nutrients and removal of waste products
The fetus in the uterus
The placenta & umbilical cord: extended
What is the the placenta and the umbilical cord?
During the gestation period the fetus develops and grows by gaining the glucose, amino acids, fats, water and oxygen it needs from the mother’s blood
The bloods run opposite each other, never mixing, in the placenta
The fetus’s blood connects to and from the placenta by the umbilical cord
The mother’s blood also absorbs the waste from the fetus’s blood in the placenta; substances like carbon dioxide and urea are removed from the fetus’s blood so that they do not build up to dangerous levels
Movement of all molecules across the placenta occurs by diffusion due to difference in concentration gradients
The placenta is adapted for this diffusion by having a large surface area and a thin wall for efficient diffusion
Toxins and pathogens
The placenta acts as a barrier to prevent toxins and pathogens getting into the fetus’s blood
Not all toxin molecules or pathogenic organisms (such as viruses, eg rubella) are stopped from passing through the placenta (this usually depends on the size of the molecule)
This is why pregnant women are advised not to smoke during pregnancy as molecules like nicotine can pass across the placenta
Placenta and umbilical cord diagram
The placenta
Examiner Tips and Tricks
It is worth learning at least two specific substances that move in either direction across the placenta – this is a common exam question and non-specific answers such as ‘waste products’ and ‘nutrients’ will not get any marks!
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