State four molecules transported by the blood.

Outline the control of the heartbeat.

Discuss the cause, transmission and social implications of AIDS.

a. example of a nutrient e.g. glucose;

b. oxygen/O₂;

c. carbon dioxide/CO₂;

d. nitrogen/N₂;

e. hormones;

f. antibodies;

g. urea;

a. is myogenic;

b. pacemaker / SA node / OWTTE;

c. stimulates atria to contract;

d. leading to contraction of ventricles;

e. (autonomic) nerves can alter the pace;

f. (by secretion of) epinephrine/adrenaline/norepinephrine/noradrenaline increase the pace;

g. (by secretion of) acetylcholine reduces the pace;

h. adrenal glands release epinephrine/adrenaline;

i. carried by blood to heart;

j. to increase pace;

cause: [4 max]

a. AIDS caused by HIV;

b. penetrates (T) lymphocytes;

c. (envelope) (glyco)protein and cell receptors involved;

d. reverse transcriptase enables DNA to be produced from viral RNA; (reject DNA transformed into RNA)

e. number of lymphocytes reduced over years;

f. results in lower immunity;

g. other illnesses develop (as result of lower immunity);

h. AIDS is the observed syndrome when final stages of infection develop / OWTTE;

transmission: [3 max]

i. HIV transmitted through blood/sexual contact/body fluids/placenta/childbirth/ breastfeeding;

j. distribution/transmission uneven around the world;

k. transmission risk increased depending on society’s traditions/beliefs/behaviour;

l. (rare minority of) individuals do not have cell receptors and do not develop AIDS;

m. condoms/latex barriers only protection against transmission through sexual contact;

social implications: [3 max]

n. treatment expensive;

o. discrimination against victims;

p. moral obligation of wealthy countries to help poorer countries;

q. economic consequences / loss of wage earners etc.;

r. increase in the number of orphans;

s. comment on traditions/beliefs/behaviour; (if not already awarded in transmission) [8 max]

Generally this question was answered well. Weaker candidates did not give an example of a nutrient. The weakest candidates wrote about red blood cells, white blood cells and water being carried in the blood.

Some candidates mentioned that the heart is myogenic but most based heartbeat control on the pacemaker. Answers included stimulation of the atria but not the subsequent contraction of ventricles. Many did not seem to understand that the two atria contract simultaneously followed by simultaneous contraction of the two ventricles. Descriptions of neural control and hormonal control varied greatly. The idea that secretion of acetylcholine by nerves can reduce the pace was never given. A few candidates only knew heart anatomy so drew a diagram and described flow of blood through the heart, to no avail.

The AIDS question was generally answered well. Though the marks gained were spread over cause, transmission and social implications, there were gaps. Many candidates did not seem to understand how HIV affects lymphocytes. There was almost no mention of reverse transcriptase enabling DNA to be produced from RNA. Despite much detail about how the virus is transmitted, few candidates mentioned the uneven transmission of HIV throughout the world. Many candidates wrote in depth about the social implications of AIDS. Often, the ideas were exceptionally well-expressed.