Calculate the power of magnification of the image.

State the diameter of the pore labelled X.

List two examples of how human life depends on mitosis.

Describe the importance of stem cells in differentiation.

The graphs below show the normal menstrual cycle.

Predict, with a reason, how the graphs will change if the woman becomes pregnant.

List two roles of testosterone in males.

50 000 (Accept answers in the range of 50 000 to 53 000)

0.1 μm (units required)
Allow answers in the range of 0.09 μm to 0.12 μm.

Award [1] for any two of the following.
growth/production of (extra) body cells; (do not accept cell growth)
first stage of spermato/oo/gametogenesis / forming oogonia/spermatogonia;
embryo development;
wound healing / (tissue) repair / hair growth / replacement of skin cells; (do not accept repairing cells)
clonal selection / division of lymphocytes (for antibody production);
Do not accept asexual reproduction. Do not award a mark if one of the first two answers is incorrect.

stem cells are undifferentiated cells;
embryo cells are stem cells;
stem cells can differentiate in many/all ways / are pluripotent/totipotent;
differentiation involves expressing some genes but not others;
stem cells can be used to repair/replace tissues/heal wounds;

estrogen and progesterone do not drop/continue rising (after day 21);
because corpus luteum continues to secrete them / embryo secretes HCG;
to maintain/increase uterus lining/endometrium;

Award [1] for any two of the following.
pre-natal development of male genitalia;
stimulates spermatogenesis / sperm production;
maintenance of sex drive/libido;
puberty / development of secondary sexual characteristics / penis growth / pubic hair / body hair / facial hair / beard / deeper voice;
Do not award the mark if one of the first two roles given is incorrect.

In part (a), only about half of candidates calculated the magnification of the electron micrograph correctly. This involved measuring the length of the scale bar in millimetres and multiplying by 1000, to convert the length to micrometres. Candidates then needed to know that magnification is calculated by dividing the size of the image, in this case the actual length of the scale bar, by the size of the specimen, in this case the length indicated on the scale bar.   

Some answers could not possibly have been correct and candidates should be encouraged to test whether their answer is sensible. This could have been done by using the answer to calculate the actual size of the nuclear pores on the micrograph, which were about five millimetres across or 5000 micrometres on the micrograph.

This task was much easier as the nuclear pore labelled X was half of the diameter of the scale bar, so all that was necessary was to divide its length by two

A variety of answers was accepted here and many candidates gave two of these. Frequent answers that were not accepted were repair of cells, antibody production, production of gametes and production of zygotes. Although some of these processes involve mitosis, it was necessary to specify how.

The wording of this question was unusual and as a result answers were very varied. Marks were awarded for correct statements about the undifferentiated state of stem cells, their capacity to differentiate in different ways and their role in repair of tissues. Some candidates stated that stem cells could be used to treat leukemia or Parkinson's disease, but some details were required for a mark to be awarded.  

This was based on AS 11.4.10 and AS 11.4.12. Many candidates used their understanding of the hormonal control of pregnancy to predict the changes in the levels of estrogen and progesterone correctly.

About two thirds of candidates gave two roles of testosterone that examiners accepted. Where a limited number of answers is allowed, candidates should be advised to give the answers which they think are most significant. If candidates gave two secondary sexual characteristics, such as axillary hair and pubic hair, the mark was not awarded as other more important roles had been omitted.