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Reproduction in animals (Reproduction in humans (sperm are produced in the…
Reproduction in animals
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Transfer of sperm to egg
Sperm structure
head: nucleus, sac of enzymes to penetrate membrane around egg
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Fish release sperm into the water to swim through eggs laid by female, KA external fertilisation
Birds and mammals ejaculate sperm into the bodies of females, KA internal fertilisation, preceded by sexual intercourse
Fertilisation
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- a sperm penetrates the cell membrane and the sperm nucleus enters
- the sperm nucleus and egg nucleus fuse
- an extra membrane now prevents any more sperm entering
Fertilisation provides an additional source of genetic variation as the sperm and egg are genetically different
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Reproduction in humans
sperm are produced in the testes by meiosis
–> during sexual intercourse they pass along the sperm duct and are mixed with fluid from the seminal vesicles
–> the mixture is KA semen
Semen is ejaculated through the urethra into the vagina of the female
–> the sperm swim towards the oviducts
Each month an egg is released into an oviduct from one of the ovaries, KA ovulation
–> if an egg is present in the oviduct it may befertilised
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Embryo develops a placenta
–> gets rid of waste products eg. urea, carbon dioxide
–> obtain materials eg. oxygen and nutrients
–> secretes female hormones, particularly progesterone – maintain the pregnancy and prevent embryo from aborting
A membrane KA the amnion encloses developing embryo
–> secretes amniotic fluid – protects the developing embryo against sudden movements and bumps
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At 9 months there is no room left for the fetus to grow
–> sends a hormonal signal to the mother to begin birthing
Stages of Birth
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Muscles of the uterus contract quite strongly and tears the amnion, allowing amniotic fluid to escape, KA waters breaking
strong contractions of the muscles of the uterus push the baby's head through the cervix and then through the vagina to the outside world
- delivery of the afterbirth
the uterus continues to contract and pushes the placenta out, with the membranes that surrounded the baby, KA the afterbirth
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