Human Reproduction - Part 3 (T3)

Question 1

Describe how an egg is specially adapted to carry out its specific functions..

Answer 1

• an ovum is one of the largest cells in the human body and can be without a microscope
• each ovum has a haploid nucleus
• it also has a large cytoplasm which contains the nutrients and mitochondria needed for mitosis after fertilisation
• each ovum also has a special cell membrane which only allows one sperm to fertilise it

Question 2

Describe how sperms cells are specially adapted to carry out their specific functions…

Answer 2

• each sperm cell also has a haploid nucleus and a tail (flagellum) which propels it through the cervix, uterus and fallopian tube towards the ovum
• each sperm cell has many mitochondria to produce the energy it requires for its journey through the female reproductive system
• sperm cells also have special enzymes called acrosomes which allow them to penetrate through the cell membrane of the ovum to enable fertilisation

Question 3

What are acrosomes?

Answer 3

Special enzymes in sperm cells which allow them to penetrate through the cell membrane of the ovum to enable fertilisation

Question 4

Describe fertilisation…

Answer 4

• the joining together or fusion of a male sperm cell with a female ovum
• when a sperm cell fertilises an ovum, their nuclei fuse so that the new cell takes 23 chromosomes from one parent and 23 from another

Question 5

What happens to the zygote once fertilisation has taken place?

Answer 5

• the zygote divides over and over by mitosis

- this cell division creates the many cells that eventually form a new individual

Question 6

All human cells except gametes have 23 pairs of chromosomes in the nucleus. What is the “23rd pair” ?

Answer 6

• the 23rd pair is the sex chromosome pair
• it controls the inheritance of gender
• in males the two sex chromosomes are different (XY)
• in females they are the same (XX)

Question 7

An animal has 36 chromosomes in each of its body cells. How many of these chromosomes came from its male parent?

Answer 7

18 (shared down the middles like humans)

Question 8

Very briefly breakdown the process from sperm cell to baby…

Answer 8

• during intercourse the sperm cells travel along the sperm duct and mix with the fluid from the glands to form a mixture known as semen
• the semen is ejaculated into the females vagina
• the sperm cells enter the uterus through the cervix and travel to the fallopian tubes
• if a sperm cell meets with an ovum then fertilisation takes place
• if an ovum is fertilised it produces a zygote which then divides by mitosis to form a ball of cells called an embryo
• the embryo implants into the lining of the uterus and develops into a foetus and eventually a baby

Question 9

What main four points does a developing foetus rely on its mother for?

Answer 9

• protection
• oxygen
• nutrients (food and water)
• removal of waste substances (eg: carbon dioxide and urea)

Question 10

What is the placenta and what does it do?

Answer 10

• the placenta is responsible for providing oxygen and the nutrients as well as removing the waste substances between the mother and the foetus
• it grows into the wall of the uterus and is made of tissues from both the mother and the embryo
• it is joined to the foetus by a tube called the umbilical cord
• the mother and foetal bloods do not mix, but the placenta allows substances to pass between the two blood supplies

Question 11

the mother and foetal bloods do not mix, but the placenta allows substances to pass between the two blood supplies. Explain…

Answer 11

• oxygen and nutrients and food and water diffuse across the placenta from the mother to the foetus
• waste substances such as carbon dioxide and urea diffuse across the placenta from the foetus to the mother so the mother can remove them

Question 12

During pregnancy, what protects the foetus?

Answer 12

• it is protected by the uterus and a membrane called the amnion or amniotic sac
• the amnion secretes fluid called the amniotic fluid which protects the developing embryo from jolts and acts as a shock absorber

Question 13

What are the three stages involved in birth?

Answer 13

• the cervix dilates to allow the baby to pass through and the muscles in the wall of the uterus contract, rupturing the amnion thus allowing the escape of the amniotic fluid. This is called the ‘breaking of the water’
• strong contractions of the uterine muscles first push the head of the baby out through the cervix and vagina to the outside world
• after the baby has been born, the uterus continues to contract to push out the placenta and the membranes which surrounded the baby. This is known as the ‘afterbirth’