16.4 Sexual Reproduction in Humans (Cambridge (CIE) O Level Biology): Flashcards
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What is the function of the testis?
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What is the function of the testis?
To produce sperm (male gametes) and the hormone testosterone.
What is the function of the scrotum?
To hold the testes outside the body, keeping sperm slightly cooler than body temperature.
What is the function of the sperm duct?
Carries sperm from the testis to the urethra, where it mixes with fluids from the glands.
What is the function of the prostate gland?
Produces seminal fluid that is added to sperm and provides them with nutrients.
Define oviduct.
The tube connecting the ovary to the uterus, where fertilisation occurs; lined with ciliated cells.
What is the function of the ovary?
Contains and matures ova (female gametes), which are released when hormones are produced.
What is the function of the uterus?
A muscular bag where the fertilised egg implants and develops into a fetus.
What is the function of the cervix?
A ring of muscle at the lower end of the uterus that keeps the developing fetus in place.
In the female reproductive system, fertilisation occurs in the .
In the female reproductive system, fertilisation occurs in the oviduct.
The produce sperm and the hormone testosterone.
The testes produce sperm and the hormone testosterone.
True or False?
The scrotum keeps the testes slightly cooler than body temperature.
True.
The scrotum holds the testes outside the body so sperm are kept slightly below body temperature.
True or False?
Fertilisation normally takes place in the uterus.
False.
Fertilisation normally occurs in the oviduct; the uterus is where the embryo implants and develops.
Define fertilisation in humans.
The fusion of the nuclei of a male gamete (sperm) and a female gamete (egg).
Where does fertilisation occur in humans?
In the oviduct.
What is formed when a sperm and egg nucleus fuse?
A zygote, which divides to form an embryo.
How is a sperm cell adapted to reach and fertilise an egg?
has a flagellum (tail) to swim to the egg
has enzymes (acrosome) to digest through the egg's coat
has many mitochondria to release energy
How is the egg cell adapted for fertilisation?
stores energy in its cytoplasm for the dividing zygote
has a jelly coat that changes after fertilisation to block other sperm
Why does a sperm cell contain many mitochondria?
To release energy from respiration so the flagellum can move for swimming.
What is the function of the enzymes in the head of a sperm?
To digest through the jelly coat and membrane of the egg cell.
In humans, fertilisation takes place in the .
In humans, fertilisation takes place in the oviduct.
A sperm cell has a that enables it to swim to the egg.
A sperm cell has a flagellum (tail) that enables it to swim to the egg.
True or False?
The egg cell is much larger than the sperm cell.
True.
The egg is a large cell, while the sperm is very small — mostly a head and tail.
True or False?
Sperm cells are unable to move on their own.
False.
Sperm are capable of locomotion, swimming with their flagellum; it is the egg that cannot move by itself.
Define zygote.
The cell formed when a sperm nucleus and an egg nucleus fuse at fertilisation.
Define implantation.
When the embryo embeds itself in the thick lining of the uterus.
Define placenta.
The organ that exchanges substances between the mother's and fetus's blood by diffusion.
What happens to the zygote as it travels to the uterus?
It divides several times (by mitosis) to form a ball of cells called an embryo.
When does an embryo become known as a fetus?
After about 12 weeks, once the organs have formed and the placenta has developed.
What is the function of the amniotic sac and fluid?
The amniotic fluid cushions and protects the fetus from bumps to the mother's abdomen.
What is the function of the umbilical cord?
Joins the fetus to the placenta for the exchange of nutrients and removal of waste.
Which substances pass from the mother to the fetus across the placenta?
glucose
amino acids
oxygen (also fats and water)
Which waste substances pass from the fetus to the mother across the placenta?
carbon dioxide
urea
Substances move across the placenta by down concentration gradients.
Substances move across the placenta by diffusion down concentration gradients.
The human gestation period lasts about months.
The human gestation period lasts about nine months.
True or False?
Some viruses, such as rubella and HIV, can cross the placenta to the fetus.
True.
The placenta acts as a barrier, but small molecules and some viruses can still pass across to the fetus.
True or False?
The mother's and fetus's blood mix directly in the placenta.
False.
The two blood supplies run close together but never mix; substances are exchanged by diffusion.
What controls secondary sexual characteristics in males and females?
Hormones — testosterone in boys and oestrogen in girls.
State three female secondary sexual characteristics.
breasts develop
body hair grows
hips widen (and the menstrual cycle begins)
State three male secondary sexual characteristics.
penis and testes grow
facial and body hair grow
voice breaks (and muscles develop)
Define ovulation.
The release of an egg from the ovary, usually around day 14 of the menstrual cycle.
Define menstruation.
The breakdown of the thickened uterus lining, lost through the vagina (a 'period').
How long is an average menstrual cycle, and when does ovulation occur?
About 28 days, with ovulation around day 14 (roughly halfway).
What is the role of oestrogen in the menstrual cycle?
It causes the uterus lining to thicken and the egg to mature; it is produced by the ovary.
What is the role of progesterone in the menstrual cycle?
It maintains the thickened uterus lining; when it falls, the lining breaks down (menstruation).
Ovulation usually occurs around day of a 28-day menstrual cycle.
Ovulation usually occurs around day 14 of a 28-day menstrual cycle.
The hormone controls the development of male secondary sexual characteristics.
The hormone testosterone controls the development of male secondary sexual characteristics.
True or False?
A fall in progesterone causes the uterus lining to break down.
True.
When progesterone levels drop, the uterus lining can no longer be maintained and breaks down, causing menstruation.
True or False?
Oestrogen controls the secondary sexual characteristics in boys.
False.
Testosterone controls male secondary sexual characteristics; oestrogen controls them in girls.
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