| Date | November 2011 | Marks available | 8 | Reference code | 11N.2.HL.TZ0.6 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 6 | Adapted from | N/A |
Question
Describe the production of semen.
Explain the structure and function of the placenta.
Outline the hormonal control of birth.
Markscheme
sperm produced by meiosis;
in testis/seminiferous tubules;
sperm are stored/mature in the epididymis;
sperm able to swim;
seminal vesicles add fluid;
(seminal) fluid rich in fructose;
prostate gland adds fluids;
fluid rich in proteolytic enzymes/citric acid/acid phosphatase/lipids/minerals;
(semen) contains basic amines/alkaline substances;
which neutralizes acid/hostile environment of the vagina;
disc-shaped structure;
connected to the fetus by an umbilical cord;
placenta is embryonic and maternal tissue;
placental villi increase the surface area (for exchange);
fetal capillaries in placenta/placental villi;
inter-villous spaces/sinuses through which mother’s blood flows;
fetal and mother’s blood do not mix / small distance between fetal and mother’s blood;
transfer of foods/nutrients/glucose from mother to fetus;
fetal gas exchange/transfer of oxygen from mother to fetus;
transfer of excretory/waste products/CO2 from fetus to mother;
transfer of antibodies/hormones from mother to fetus;
secretion of estrogen/progesterone/HCG;
Allow reference to embryo instead of fetus throughout.
at about 38 to 40 weeks pregnancy/end of pregnancy/progesterone levels decrease;
removes inhibition of oxytocin secretion;
(oxytocin) released from (posterior) pituitary;
oxytocin stimulates uterus contraction;
cervix widens/dilates;
increase in oxytocin increases rate and intensity of contractions;
positive feedback;
Examiners report
The production of semen and spermatogenesis were confused by many candidates. Better candidates were able to give a very impressive account of the process, though many focused too much on spermatogenesis rather than on the other components of semen.
In spite of the fact that the structure and function of the placenta seem to have been on several papers in the last few years, they were not very well-known at all. Most gained some function marks for gas exchange and transfer of nutrients and waste, but the structure was not well known.
Most knew something of the hormonal control of birth. However weaker candidates started at conception and seemed intent on explaining the whole process.
