18 — reproduction in humans

Question 1

Testis (singular) (plural: testes)

Answer 1

produces sperms and male sex
hormones such as testosterone

Question 2

Scrotum (scrotal sac)

Answer 2

pouch-like sacs located outside
the body cavity to help
maintain a lower temperature
for the development of sperms

Question 3

Sperm duct (vas deferens)

Answer 3

the pathway travelled by sperms
after they are released from the
testis

Question 4

Seminal vesicle

Answer 4

stores sperms temporarily
before they are released
through the urethra

Question 5

Urethra

Answer 5

a tube that extends from the
bladder, through the penis, to
outside the body

Both urine and semen exit the
body through the urethra, but
never at the same time.

Question 6

Penis

Answer 6

erectile organ that becomes
erect and hard during sexual
intercourse in order to enter
and deposit semen into the
vagina

Question 7

Erection

Answer 7

An erection occurs when the
spongy tissue in the penis
is filled with blood.

Question 8

why the need for many sperms

Answer 8

• Increases chance of fertilising the egg by increasing ratio of sperms to egg (e.g. 100,000,000:1)
• Fast-swimming sperm can reach the egg in half an hour, while others may take days.
• The sperm can live up to 48-72 hours.
• Only a few hundred will even come close to the egg because of the many natural barriers that exist in a woman’s body.

Question 9

Ovary functions [3]

Answer 9

Ovaries produce female hormones, oestrogen and progesterone which are used for growth and repair of the uterine lining and further thickening and maintenance of thickness of uterine lining respectively during menstrual cycle. [2]

Ovaries produce ova which will be released for fertilisation where its haploid nucleus will fuse with the haploid nucleus of the sperm to produce a diploid zygote. [1]

Question 10

Oviduct (fallopian tube)

Answer 10

a narrow muscular tube with a
funnel-like opening at the ovary that transports eggs to the uterus by peristalsis of the muscular wall and sweeping action of the cilia; site of fertilisation.

Question 11

Uterus (womb)

Answer 11

Site of implantation of embryo and the location where the fetus
develops; it has elastic muscular walls that enable contraction during birth to expel the fetus

Question 12

uterine lining (endometrium)

Answer 12

the soft, smooth inner lining of the uterus rich in blood supply that is important for embryo implantation

Question 13

Cervix

Answer 13

the circular ring of muscle at
the lower end of uterus which enlarges to allow passage of the fetus during birth

Question 14

State the differences between the male gamete and female gamete in terms of structure, motility and numbers.

Answer 14

Structure:
M:
* Has a head, mid body and a
flagellum
* Haploid nucleus contains either X or
Y chromosome
* 60micrometer long

F:
* Spherical in shape
* Haploid nucleus contains
only X chromosome
* Diameter 120m to 150m

Motility:
M: motile
F: non-motile

Numbers:
* Numerous sperms are produced
throughout the life from puberty
onwards
* Large number of sperms released
during each ejaculation
* Number of eggs
determined at birth
* Usually only one matured
egg is released per month

Question 15

The menstrual cycle

Answer 15

The cycle of events that takes place in the female reproductive organs every month

average length of a menstrual cycle
is 28 days.
* There is a natural variation in the length of the menstrual
cycle; ranging from 21 to 33 days.
* The menstrual cycle can be affected by stress, illness,
unbalanced diet, and/or malnutrition.

Question 16

Menstruation

Answer 16

The monthly discharge of blood from the uterus via the vagina due to the breakdown of uterine lining

Question 17

Describe and explain the changes in the concentration of oestrogen and progesterone during the menstrual cycle. [4]

Answer 17

Oestrogen and progesterone control the menstrual cycle. Estrogen: high level needed for ovulation; repairs the uterus lining. Progesterone: high level needed to stop development of more ova; maintains the uterine lining. [1]

From day 6 to 13, developing follicles secretes oestrogen for the repair and growth of the uterine lining. [1]

On day 14, ovulation occurs whereby a mature egg/ovum is released from the ovary. [1]

From day 15 to 28, oestrogen level drops while progesterone is produced by the ovaries to maintain and further thicken the uterine lining, supplying it with blood capillaries to prepare for implantation of embryo. [1]

If fertilisation does not occur, levels of oestrogen and progesterone drops sharply and uterine lining can no longer be maintained or breaks down, resulting in menstruation and the repeat of the menstrual cycle. [1]

Question 18

If fertilisation does not occur

Answer 18

1. Egg/ovum breaks down
2. High concentration of progesterone inhibits LH production. Lowered LH levels result in the corpus luteum breaking down.
3. Progesterone is no longer secreted.
4. Uterine lining breaks down
5. Uterine lining is discharged together with blood through the vagina (This marks the beginning of menstruation.)
6. Menstrual cycle repeats

Question 19

If fertilisation occurs

Answer 19

1. The fertilised egg becomes a zygote, which develops mitotically into an embryo.
2. The embryo embeds itself in the uterine lining and is implanted.
3. The embryo secretes a hormone (human chorionic gonadotropin,
   hCG) that prevents the corpus luteum from breaking down.
4. The corpus luteum continues to secrete estrogen and progesterone until the placenta forms and is able to take over the production of both hormones.

Question 20

What would happen to an embryo if levels of progesterone suddenly drop during pregnancy?

Answer 20

Miscarriage can occur as the thickness of the uterine lining cannot be maintained for the
embryo to obtain sufficient nutrients and oxygen from the blood vessels.

Question 21

Describe the blood transported by umbilical arteries and umbilical vein.

Answer 21

• To transport blood away from the heart and towards the fetus’s heart
• Umbilical arteries carry deoxygenated blood while umbilical vein carries oxygenated blood.

Question 22

Functions of the umbilical cord

Answer 22

Umbilical vein: transports oxygenated blood and food
substances such as glucose and amino acids from the placenta to the fetus

Umbilical arteries: transport deoxygenated blood and metabolic waste products (urea and carbon
dioxide) from the fetus to the
placenta

The blood system of the mother and the fetus cannot mix due to possible agglutination and difference in blood pressure of the mother and the fetus which may kill the fetus.

Question 23

Functions of the amniotic fluid

Answer 23

• found in amniotic sac which encloses the fetus in the amniotic cavity
  1. Allows the fetus to move freely
  during growth
  2. Lubricates and reduces friction in the vagina during birth
  3. Protects the fetus against physical injury by absorbing shock
  4. Supports and cushions the fetus
  5. Prevents temperature fluctuations

Question 24

Acquired Immune Deficiency Syndrome (AIDS)

Answer 24

• AIDS is a STI caused by the Human
  Immunodeficiency Virus (HIV).
• HIV destroys the body’s immune system by attacking white blood cells, thus making infected individual prone to many
  infections
• A person infected with AIDS is not able to produce sufficient antibodies to protect
  him or herself from other infections.
• Infections that are normally mild may become fatal for a person with AIDS.

Symptoms
1. Severe diarrhoea that lasts for months
2. Pneumonia
3. Kaposi’s sarcoma
4. Brain infection
5. Widespread tuberculosis
6. Chronic fever

Question 25

How to prevent HIV infection [3]

Answer 25

Controlling spread of HIV: [3]

• ensuring use of sterlised needles in medical equipment [1]
• keeping to one sex partner or do not have sex [1]
• not sharing instrument that will break the skin and be contaminated with blood, e.g. toothbrush and razors. [1]

Question 26

Describe the menstrual cycle from Day 1 to Day 14 and explain the roles of the hormones in stimulating the changes. [6]

Answer 26

Day 1-5 (Menstrual flow stage)
● Menstruation occurs. Both oestrogen and progesterone level are low and menstruation occurs as uterine lining could not be maintained. [1]
● During menstruation, the uterine lining breaks down and flows out through the vagina. Damage to blood vessels causes bleeding. [1]

Day 6-13 (follicle stage)
● Follicle in one of the ovaries start to develop in response to follicle stimulating hormone from pituitary gland. [1]
● The developing follicle secrete hormone, oestrogen for the repair and growth of the uterine lining.[1]
Level of estrogen is the highest.

Day 14 (ovulation stage)
● Follicle matures to become Graafian follicle
● Surge /increase in oestrogen production caused the pituitary gland to release the luteinizing hormone. [1]
● Ovulation occurs whereby a mature ovum is released from the Graafian follicle.[1]

Corpus Luteum stage (day 15 - 28)
* Progesterone prepares the uterine lining for the fertilised egg by causing it to thicken further, and supplying it with blood capillaries.
* Progesterone inhibits ovulation

Question 27

Prostate gland

Answer 27

Produces alkaline, milky fluid that contains nutrients and enzymes which nourish and activates the sperms and helps them to swim towards the egg.

Question 28

Describe fertilisation and early development of the zygote [6] + [4] + [5]

Answer 28

When the sperms reach the ovum, sperms release acrosome enzymes to break down the ovum membrane. Only one sperm nucleus enters the ovum; [1] As soon as a sperm enters the egg, the membrane of the egg changes such that no other sperms can enter. The sperms that were unable to fertilise the egg eventually die.
Fertilisation occurs when the nucleus of the sperm fuses with the nucleus of the ovum, forming a zygote; [1]
The zygote divides by mitosis to form a ball of cells, embryo; [1]
Embryo moves along the oviduct towards the uterus by peristalsis of the oviduct muscles and sweeping motion of the cilia lining the inner surface of the oviduct; [1]
and is implanted in the uterine lining of the uterus during implantation for further development; [1]
Corpus luteum in the ovary continues to produce progesterone to maintain the thickness of uterine lining until the formation of the placenta takes over; [1]

The fertilised egg, zygote continues to divide by mitosis to form a ball of cells called an embryo. [1]
The embryo travel along the oviduct towards the uterus by the contraction of the oviduct muscles via peristalsis [1] and with the help of the sweeping motion of cilia lining the inner surface of the oviduct. [1]
Embryo implants into the uterine lining of the uterus during implantation. [1]

[5]:

After fertilisation, Zygote divide by mitosis to become a ball of cells called embryo.[1]
Embryo move towards uterus by peristalsis by the wall of the fallopian tube and sweeping motion of the cilia.[1]
Embryo implanted in the uterine lining/wall of uterus. [1]
In the ovary, Graafian follicle develops into corpus luteum, which secretes progesterone to maintain the thickness of the uterine lining. [1]
Embryonic villi grow into the maternal uterus lining forming the placenta which becomes the site of exchange of substances between the fetus and the mother through the umbilical cord. [1]
Amniotic sac is formed around the fetus with amniotic fluid to cushion the fetus against shock.

(along with any 2 more points):

Finger-like projections called villi, containing the blood vessels from the embryo, grow into the uterine lining, forming the placenta.

The placenta secretes progesterone and oestrogen, maintaining the thickness of uterine lining.

In the placenta, oxygen and nutrients diffuse from maternal to foetal capillaries, and are delivered to the foetus via the umbilical cord, while metabolic waste products such as urea and carbon dioxide are removed.

The amniotic sac develops, containing amniotic fluid that protects foetus from physical injury/allows for movement for muscular development/trains the foetus’ digestive system.

Question 29

Define implantation

Answer 29

The process where the embryo embeds itself in the uterus lining

Question 30

If fertilisation occurs, what will happen to the thickness of the uterine lining after day 28? Explain your answer. [3]

Answer 30

If fertilisation occurred, the ovary continues secreting oestrogen and progesterone, keeping their levels high.

Hence, these hormones maintain the uterine lining even after day 28, in preparation for the implantation of the embryo.

The lining does not break down, and there is no menstruation.

Question 31

On which days of the menstrual cycle is the woman most fertile? Explain your answer. [4]

Answer 31

Ovulation occurs on day 14, where a mature ovum is released from an ovary into an oviduct.

The egg can be fertilised up to 48 hours (2 days) after its release from the ovary.

Sperms can live for three to four days in the female reproductive system.
Therefore, if sexual intercourse takes place between days 11 to 16, there is a higher chance of fertilisation. This period is known as the fertile period.

Thus the fertile period, the days where sexual intercourse would lead to the highest chance of pregnancy, is from day 10 to 15.

The rest of the days make up the infertile period of the menstrual cycle.

Question 32

Describe the functions of the placenta during pregnancy. [4]

Answer 32

The placenta secretes progesterone, to maintain the thickness of the uterine lining throughout pregnancy. [1]

The placenta is the site of exchange of substances between mother
and fetus by diffusion whereby nutrients such as glucose, amino acids and oxygen will diffuse from the mother’s blood to the fetus’s blood across the placenta/ Metabolic waste products such as urea and carbon dioxide will diffuse from the fetus’s blood to the mother’s
blood, across the placenta; [1]

Antibodies from the mother’s blood will diffuse into the fetus’s blood to protect the fetus from diseases; [1]

Blood system of the mother and fetus are separated by blood spaces at the placenta to prevent mixing and possible agglutination of blood due to difference in blood pressure and blood type, which may potentially harm foetus; [1]

Question 33

Explain why the maternal and foetal blood vessels are not directly connected. [2]

Answer 33

Maternal and foetal blood types may be incompatible, and direct mixing of blood would lead to agglutination of red blood cells which is dangerous both mother and foetus.
The mother’s blood pressure is higher than that of the foetus, which may burst foetal blood vessels if they were connected.

Question 34

Describe the ways in which HIV can be transmitted. [4]

Answer 34

Unprotected sexual intercourse, where semen containing HIV comes into contact with the mucous membrane of an uninfected female’s vagina.
Or when vaginal fluids containing HIV come into contact with the mucous membrane of an uninfected male’s urethra.
By sharing contaminated needles, such as between drug addicts.
By blood transfusion with blood from an infected person.
During pregnancy, where the virus travels from an infected mother to the foetus.

Question 35

Suggest a role for the cilia found in oviduct. [1]

Answer 35

Cilia lining the inner surface of the fallopian tube sweep the fertilised egg/ zygote/ embryo along the fallopian tube/ oviduct towards the
uterus. [1]

Question 36

Compare the progesterone levels in the pregnant woman to the progesterone levels expected in a healthy young woman who is not pregnant during the same 9 months. [4]

Answer 36

Similarity:
The progesterone level of the pregnant woman in the first 3 months is at about 25-30 arbitrary units [1] which is about the same level as the progesterone level of the non-pregnant woman at day 22/ highest level of the menstrual cycle. [1]

Difference:
The progesterone level of the pregnant woman changes along the
9 months with low levels at 30 arbitrary units for the first 3 months before increasing to 100-150 arbitrary units for the next 5 months and reaching the maximum of 250 arbitrary units at the 9th month.
[1] while the progesterone level of the non-pregnant woman shows a regular repeated pattern per month for 9 months with the maximum level reaching 25 arbitrary units in each month. [1]

Question 37

Ovulation

Answer 37

The release of a mature egg from the ovary around day 14 of the menstrual cycle