Chapter 12B Reproduction In Humans

Question 1

State one function of amniotic fluid [1] (2011/A5)

Answer 1

• Protect the fetus from physical harm as a shock absorber
• Cushions the
  fetus from shock
• Protects the fetus against physical injury
• Allows the fetus a certain degree of movement (misconception: to acquire food)

Question 2

Name two substances that pass from mother to fetus during pregnancy. [2] (2011/A5)

Answer 2

Antibodies/ glucose/ amino acids/ oxygen/ fatty acids/ glycerol/ named vitamin/ named mineral salt

Question 3

Describe the sequence of events thay occur after a human egg cell is fertilised which enable it to develop and survive in the uterus. [5] (2017/A5b)

Answer 3

1. The Zygote divides by mitosis to become a ball of cells called an embryo.[1]
2. The embryo move towards the uterus by the peristalsis of the wall of the fallopian tube and the sweeping motion of the cilia.[1]
3. Embryo embeds in the uterine lining/wall of uterus during implantation. [1]
4. In the ovary, Graafian follicle develops into corpus luteum, which secretes progesterone to maintain the thickness of the uterine lining. [1]
5. Embryonic villi grow into the maternal uterine lining forming the placenta which becomes the site of exchange of substances between the fetus and the mother. [1]

[5] Differentiate between the
terms zygote, embryo and fetus
Show correct relationship
between placenta, umbilical cord and amniotic sac

Question 4

Describe the process and outline the early development of the embryo. [6] (2018/B10 O)

Answer 4

1. When the sperm reaches the ovum, it releases enzymes from the acrosome to break down the ovum membrane. Only one sperm nucleus enters the ovum;
2. Fertilisation occurs when the haploid nucleus of the sperm fuses with the haploid nucleus of the ovum, forming a diploid zygote;
3. The zygote divides by mitosis to form a ball of cells, the embryo.
4. The embryo moves along the oviduct towards the uterus by peristalsis of the oviduct muscles and sweeping motion of the cilia,
5. and is implanted in the uterine lining/wall of the uterus;
6. The Corpus luteum in the ovary continues to produce progesterone to maintain the thickness of the uterine lining until the formation of the
   the placenta takes over;

Question 5

Describe the function of the placenta during pregnancy [4] (2018/B10 OR)

Answer 5

• The placenta produces progesterone to maintain and thicken the uterine lining during pregnancy;
• The placenta is the site of the 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;
• Antibodies from the mother’s blood will diffuse into the fetus’s blood to protect the fetus from diseases;
• it allows the blood of the fetus and mother to flow close to each other without mixing so as to facilitate fast material exchange/diffusion through membranes between mother and fetal blood;

Question 6

The ______ Produces sperms and male sex hormone, testosterone (self)

Answer 6

Testes

Question 7

The _______ Keeps the testes outside the main body so that sperms can develop properly at lower temperature (self)

Answer 7

Scrotum

Question 8

The _____ ____ (___ _______) carries sperms from testes to the urethra (self)

Answer 8

Sperm duct (vas deferens)

Question 9

The ________ _____ produces alkaline, milky fluid that contains nutrients and enzymes which nourish and activates the sperms and helps them to swim towards the egg. (self)

Answer 9

Prostate gland

Question 10

The _______ Passes the sperm out of the body (self)

Answer 10

Urethra

Question 11

The _____ is made of erectile tissue, allowing it to enter and deposit sperm in the vagina (self)

Answer 11

Penis

Question 12

The _____ Produce ova/eggs and female sex hormones, estrogen and progesterone (self)

Answer 12

Ovary

Question 13

State the function of the Oviduct [3] (self)

Answer 13

• Where the ovary deposits the egg
  ● Transports eggs to the uterus by peristalsis of the muscular wall and sweeping action of the cilia.
  ● Site of fertilisation

Question 14

The ______ (____) is the site of implantation of embryo and fetus development during pregnancy (self)

Answer 14

Uterus (womb)

Question 15

The _____ is a circular ring of muscle that opens into the vagina.
It enlarges during birth to allow the passage of the foetus. (self)

Answer 15

Cervix

Question 16

The ______ where semen is deposited during sexual intercourse; birth canal (self)

Answer 16

Vagina

Question 17

The average menstrual cycle is __ days.
The menstrual cycle can range from __ to __ days. (self)

Answer 17

28, 21, 33

Question 18

Fertile period
● An egg can survive for _ days, whereas sperms can live for _ days.
● Ovulation usually occurs on day __.
● Chance of getting pregnant is highest between days __ to __.
● The rest of the days make up the infertile period. (self)

Answer 18

Fertile period
● An egg can survive for 2 days, whereas sperms can live for 3 days.
● Ovulation usually occurs on day 14.
● Chance of getting pregnant is highest between days 11 to 16.
● The rest of the days make up the infertile period.

Question 19

What happens on days 1-5 of the menstrual cycle? [4] (self)
- what marks the first day?
- hormone levels

Answer 19

● Menstruation occurs
● The first day of menstruation is the first day of the menstrual cycle
● During menstruation, the uterine lining breaks down and flows out through the vagina
- Pituitary gland secretes Follicle Stimulating Hormone (FSH)

Question 20

What happens on days 6-13 of the menstrual cycle? [2/3] (self)

Answer 20

Effects of FSH:
- Follicle-stimulating hormone (FSH) released by the pituitary gland stimulates the development of primary follicle into a Graafian follicle in one of the ovaries
- The developing follicle secretes the hormone, estrogen
Effects of Oestrogen:
- Stimulates the repair and growth of the uterine lining. the uterine lining becomes thick and spongy with blood vessels
- Oestrogen in high concentrations inhibits FSH production, preventing the maturation of more follicles.
- Oestrogen in high concentrations stimulates the pituitary gland to secrete Luteinising Hormone (LH)

Question 21

What happens on day 14 of the menstrual cycle? [3] (self)

Answer 21

effects of LH
- Induces Ovulation whereby a mature egg/ovum is released from the Graafian follicle
- Graafian follicle forms into the corpus luteum
- The corpus luteum secretes progesterone and
some estrogen

Question 22

What happens on days 15-28 of the menstrual cycle? [3/3] (self)
(fertilisation does not occur)

Answer 22

Effects of Progesterone
● Progesterone maintains the thickness of the uterine lining and supplies it with blood capillaries to prepare for the implantation of the embryo.
- inhibits ovulation
- inhibits FSH, and eventually, LH production
Chain of events:
1. The corpus luteum will degenerate due to the drop in LH, and the production of progesterone drops. The uterine lining can no longer be maintained.
2. The lining flows from the uterus together with some blood through the vagina.
3. Cycle goes back to day 1 and repeats.

Question 23

Describe fertilisation and early development of the zygote simply (self)

Answer 23

1. Semen is deposited into the vagina.
2. Sperms travel up through the cervix and uterus and enter the oviduct.
3. When the sperms reach the egg, sperms release acrosome enzymes to break down the egg membrane. Only one sperm nucleus enters the egg.
4. When the haploid nucleus of sperm fuses with the haploid nucleus of egg/ ovum to form a diploid zygote, fertilisation occurs. Fertilisation takes place in the oviduct.
5. The zygote moves from the oviduct to the uterus. It is swept by cilia and peristalsis of the oviduct muscles.
6. The zygote undergoes mitosis to form a ball of cells called the embryo, which gets implanted in the uterine lining on the wall of the uterus.

Question 24

State the functions of the amniotic sac and the amniotic fluid [1/5] (self)

Answer 24

The amniotic sac contains amniotic fluid, which allows the fetus to move within.
Amniotic fluid has the following functions:
● Supports and cushions fetus before birth
● Absorbs shock amd prevents fetus from physical injury (if the mother has a fall)
● Lubricates and reduces friction in the vagina during birth
● Allows fetus to move freely during growth
● Prevents temperature fluctuations

Question 25

Describe the function of the placenta in relation to exchange of dissolved nutrients, gases and excretory products (structural details
are not required)

Answer 25

● The placenta produces progesterone to maintain and thicken the uterine lining.
● Site of exchange of substances between mother and fetus:
1. It allows nutrients such as glucose, amino acids and oxygen to diffuse from the mother’s blood to the fetus’s blood.
2. Metabolic waste products such as urea and carbon dioxide diffuse from the fetus’s blood to the mother’s blood.
3. Antibodies from the mother’s blood can diffuse into the fetus’s blood to protect the fetus from diseases.

Question 26

Describe the function of the umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (structural details
are not required)

Answer 26

● Umbilical arteries (two) transport deoxygenated blood and metabolic waste products such as urea and carbon dioxide from the fetus to the placenta.
● The umbilical vein transports oxygenated blood, antibodies and nutrients such as glucose and amino acids from the placenta to the fetus.
● The blood system of the mother and fetus cannot mix due to possible agglutination and the difference in blood pressure between the mother and the fetus, which may kill it.

Question 27

State the modes of transmission of the human immunodeficiency virus (HIV)

Answer 27

● Having sexual intercourse with an infected person
● By sharing needles with an infected person
● Through blood transfusion with blood from an infected person
● During pregnancy when an infected mother passes the virus to her fetus

Question 28

State the ways to orevent and control the spread of the HIV virus.

Answer 28

● Keep to one sex partner
● Use a condom
● Sterilise needles before use (e.g. for ear piercing or tattooing)
● Do not share instruments likely to break the skin (e.g. razors and toothbrushes)

Question 29

What happens if fertilisation occurs? (self)

Answer 29

1. The Fertilised egg becomes a zygote. the zygote develops into an embryo
2. the embryo embeds itself into the uterine lining.
3. The embryo secretes a hormone which prevents the corpus luteum from breaking down until a structure called the placenta is formed.
4. The corpus luteum continues to secrete progesterone and oestrogen until the placenta is able to take over the production of progesterone and oestrogen.

Question 30

Describe the process of fertilisation

Answer 30

1. The egg released from the ovary is usually surrounded by a few layers of follicle cells. to penetrate the egg, the sperm releases an enzyme to disperse the particles and break down the egg membranes.
2. Only one sperm nucleus enters the egg. the haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed.
3. As soon as the sperm has entered the egg, the membrane of the egg changes so that. no other sperm can enter. The other sperm which did not fertilise the egg eventually die.

Question 31

what are the functions fo the umbilical cord? [3]

Answer 31

• Attaches the fetus to the placenta
• Contains 2 umbilical arteries that transport deoxygenated blood and metabolic waste products from the fetus to the placenta.
• One umbilical vein that transports oxygenated blood and food substances from the placenta to the fetus.

Question 32

Define puberty

Answer 32

Puberty is the stage of human growth and development in which a person becomes physically mature.

Question 33

State the specific role of ciliated cells in the oviduct [1] (CGSS/2021/A1)

Answer 33

Movement of ovum/zygote/embryo from ovary/oviduct to
uterus

Question 34

State the specific role of ciliated cells in the trachea [1] (CGSS/2021/A1)

Answer 34

Sweep up mucus that contain trapped dust/foreign particles/bacteria + up the trachea
OR
to the esophagus/larynx/nose

Question 35

Explain why fertilisation was not able to occur if sexual intercourse took place on the 8th of November [2] (CGSS/2021/A3)

Answer 35

Ovulation has not yet occurred/ovum not released/
not within fertile period day 11-17
Sperm will die before it reaches the released ovum/sperm unable to survive long enough for fertilization/sperm can only survive 3-5 days

Question 36

Alcohol causes the relaxation of muscular tissue in blood vessels.
Explain why it dangerous for people to consume alcoholic drinks while
spending a prolonged time outdoors in temperatures of approximately 5°C.

Answer 36

1. alcohol causes vasodilation of arterioles near skin/ arterioles
   unable to vasoconstrict,
2. increased blood flow to capillaries nearer to/at skin surface + increase in heat loss by conduction, convection and radiation;
3. causes further drop in body temperature/ unable to thermoregulate + possible harmful effect on body (e.g. metabolic rate too low to sustain life processes, inactive enzymes, hypothermia)

Question 37

Blood flows through an air bubble trap before it returns to the patient.
Suggest how this feature helps to protect the patient from a life-threatening complication. [2]

Answer 37

1. Air bubbles found in blood removed
2. Prevents obstruction of blood vessels + link to prevention of life-threatening complication (e.g.
   prevents lack of oxygen/nutrient flow to vital organs, heart
   attack, stroke)

Question 38

Suggest how the diets of the different groups may be different, using evidence from Fig. 6.2 [2]

Answer 38

• Larger proportion of people whose food takes a longer time to pass through gut in E. (general comparison of trend)
• Group E consumes less fibre/fewer vegetables/fruits OR group E consumes higher complex carbohydrates/protein/fat diet/more meat OR F lower protein/fat/complex carbohydrates

Question 39

Suggest two disadvantages of food passing through the digestive
tract too quickly [2] (CGSS/2021/A6)

Answer 39

Less time for food to be digested/absorbed into bloodstream OR incomplete uptake of nutrients/digestion/ malnutrition/
unbalanced diet
- Less time for water to be absorbed OR diarrhea/watery stools

Question 40

8 Three varieties of birds from the same species, A, B and C (longest beak at 30cm), are found in the bird population of a mudflat habitat. Fig. 8.1 shows the different types of beaks and the depth each bird can reach when they lower their beaks into the mud.
This species of birds prey on mussels found buried under the surface of the mud.

Answer 40

• C most has selective advantage im feeding
• it is able to reach more mussels that are buried up to a depth of 30cm/ more mussels compared to A and B
• C is able to grow, survive to maturity and reproduce more effectively than A or B
• Passing down alleles for long beak length to offspring + long beak length allele increases in frequency over a 1000 year period

Question 41

Describe the events that led to the change of diameter in the left pupil, as the student moved from 0 to 2 metres away from the light source.

Answer 41

• (Stimulus of) lowered light intensity + detected by photoreceptors/retina
• Converted to nerve impulse/ nerve impulse initiated + Impulse travels from sensory neurone + in optic nerve
• To relay neurone in brain + To motor neurone
• Reference to impulse crossing synapse
• Action of effectors – muscles of iris
  + Circular muscle contract + radial muscle rela

Question 42

Suggest a reason why the right pupil does not show the same response as the left pupil.

Answer 42

Muscles are not developed properly in right pupil / nerve endings
are not functioning properly (accept range of answers)

Question 43

Explain why a person with blood type AB cannot donate blood to a person with blood type O. [4] (CGSS/2021/B10)

Answer 43

• Donor: Antigen A and B on red blood cells of donor type AB
• Recipient: Antibodies a and b in blood plasma of recipient type O
• Binding between antigen and antibodies + causing agglutination
  of RBCs
• Blood clumps block blood vessels/disrupt flow of blood

Question 44

With reference to ABO blood groups and one other named example,
distinguish between continuous and discontinuous variation. [6] (CGSS/2021/B6)

Answer 44

• Range of phenotypes vs
  a few phenotypes Example: many different skin colour shades vs blood type A, B,
  AB, O
• controlled by many genes which may show additive effect vs. controlled by a few genes that do not show additive effect Example: skin colour controlled by many genes vs blood type controlled by three genes only IO, IA, IB
• affected by environmental changes vs. unaffected by environmental changes Example: sun causing darkening of skin, but blood type stays the same throughout lifespan