Describe four different types of transport of substances across a membrane.

Hormones such as FSH (follicle stimulating hormone) and LH (luteinizing hormone) affect the development of certain cells by binding to receptors in the plasma membranes. Outline the role of FSH and LH in the menstrual cycle.

In the placenta, many substances are transported across membranes. Explain the structure and role of the placenta.

Must be description of types not a list.
a. (simple) diffusion when molecules move down a concentration gradient directly through membrane/unaided by carrier molecule;
b. (passive transport by) facilitated diffusion through (specific) channel proteins;
c. osmosis of water via aquaporins/from area of low solute concentration to area of high solute concentration;
d. active transport against a concentration gradient using protein pumps/ATP;
e. vesicles attach to plasma membrane and release materials to exterior/ exocytosis;
f. cell membrane invaginates/pinches off to bring material to interior / endocytosis / phagocytosis;

a. FSH stimulates estrogen secretion by follicle cells;
b. at start of menstrual cycle;
c. leading to development of endometrium;
d. (FSH and) LH (rise to a peak and) causes egg to be released/ovulation;
e. causes follicle cells to secrete less estrogen/more progesterone;
f. progesterone maintains endometrium/uterine lining
g. LH promotes change of follicle to corpus luteum;
h. secretion of LH and FSH regulated by negative feedback;
i. regulated/inhibited by high estrogen and progesterone levels;
j. low progesterone levels cause menstruation;

a. disc shaped structure
b. embedded in uterus wall;
c. connected to fetus by umbilical cord;
d. contains fetal and maternal structures/tissues;
e. placental villi/maternal intervillous space provide large surface area for exchange of materials;
f. blood of fetus and mother flow close to each other (but no mixing);
g. materials exchanged/diffuse (through membranes) between mother and fetal blood;
h. oxygen/nutrients/antibodies/other substances diffuse (through membranes) to fetus;
i. CO₂ and wastes diffuse (through membranes) to mother;
j. caffeine/drugs/alcohol/viruses from mother may damage fetal development;
k. takes over role of corpus luteum (to produce hormones);
l. produces hormones/estrogen/progesterone/HCG;

Question 8 was the least popular question.  

In part a, few discussed exocytosis and endocytosis. The distinction between simple diffusion and passive diffusion was often confused. Reference to aquaporins was rare. Discussion of osmosis was generally well done.

Question 8 was the least popular question.  

In part b, the knowledge of students was adequate. The challenge for this question was structuring the response to address the demands of the question as the events within the ovary had to be linked to the events within the uterus. The role of estrogen in developing the uterine lining was well known as was the role of progesterone in maintaining the lining. They were also reasonably successful in discussing the role of LH. Students were less commonly successful with discussing the specific actions of FSH and the regulation of hormone levels.

Question 8 was the least popular question.  

Answers to part c were adequate, though it was common for the use of terminology to be poor. Most candidates were able to identify the placenta as a disc shaped structure embedded in the uterine wall that was connected to the mother via the umbilical cord. Most showed adequate understanding of the types of material exchanged within the placenta. Fewer showed adequate comprehension of the mechanism of materials exchange between the mother and the fetus. Few adequately described the structure of the placental villi or the relationship between maternal and fetal blood flow.