State when PAN was injected into the rats.

Outline the treatment given to the control group.

Distinguish between the treatment received by the PAN only group and the PAN + early edaravone group.

State the increase in protein in the urine of rats treated with PAN only between day 6 and day 9.

Compare the levels of protein during the experiment in the urine of rats treated using PAN only with those treated using PAN + early edaravone.

Evaluate whether the results support the hypothesis that a continuous dose of edaravone is better than the same drug administered over shorter periods.

Analyse the results of this experiment.

Suggest why oxidation of membrane lipids may lead to increased protein loss in the urine.

on Day 1 / at end of Day 1 / after one day / after the first day / at start of second day  

Award [0] for on Day 2 or after Day 1.

two oral doses daily of saline (for ten days);
one saline injection on Day 1/at end of Day 1/after one day/after the first day/at start of second day;
Award [0] for on Day 2 or after Day 1.

PAN + early edaravone group received edaravone for the first five days/first half of experiment/from Day 0 to Day 4 and PAN-only group did not.
To award [1] reference to both groups is required. Award [0] for 4 or 4 1 2 days.

205 mg day^-1 (units required)
Allow answers in the range of 200 to 210 mg day^-1 .

on Day 3 little/no difference / both levels very low;
protein increases in both during the experiment; Can be mentioned in separate parts of the responses.
protein higher in PAN-only group by an increasing amount / increases faster in PAN-only group;
protein levels are higher in the PAN-only group on all days / after Day 3 / on Day 6 and day 9; Accept comparative statements such as more than double.
145 versus 45 on Day 6 / 350 versus 110 on Day 9 / increase from Day 3 to Day 6 is 130 versus 35 / increase from Day 6 to Day 9 is
205 versus 65; Allow answers in the range of 5%. Accept numerical comparisons expressed as percentages.

lower (increase in) protein/greater reduction/best results with early dose rather than with continuous;
more (increase in) protein/smaller reduction/worse results with late dose than with continuous;
differences may not be significant;
partial support / does not fully support / comparison of continuous with late supports hypothesis but continuous with early does not;
timing of dose more important than duration;

PAN increases TBArs levels / TBArs levels highest in PAN-only group;
PAN causes oxidation of/damage to membrane (lipids);
edaravone reduces/prevents increase in TBArs levels;} Do not allow PAN + edaravone lowers TBArs.
edaravone prevents oxidation of membrane lipids / reduces/prevents effect of PAN;
early edaravone is more effective than late/continuous;
overlap of error bars shows differences may not be significant;
Do not allow late or continuous edaravone has no effect. Apart from the first marking point do not allow statements that are merely comparing the results.

proteins retained (in blood) during ultrafiltration (in a healthy person);
proteins are large (molecules);
proteins lost/leak from blood/into filtrate/into Bowman’s/renal capsule;
large enough pores/holes/spaces formed for proteins to pass through;
glomerulus/capillary walls/podocytes/Bowman’s/renal capsule damaged;
proteins are too big to be reabsorbed later/in proximal convoluted tubule;

This was intended to be an easy start to the question and almost all candidates answered it correctly. It was also intended to encourage candidates to think carefully about the time scale on the x-axis. It was clear that some candidates did not do this. The numbers 0, 1, 2 and so on could either be interpreted as the number of days after the start of the experiment, or the start of Day 0, Day 1, Day 2 and so on.

Many candidates scored a mark for stating that there was one injection of saline at the end of Day 0, the start of Day 1 or after one day. Far fewer pointed out that two oral doses of saline were given each day. This could be deduced from the twenty open circles in the ten-day period of the experiment.

This was answered correctly by about half of the candidates. The commonest fault was failure to state clearly when edaravone was administered. The answer, over the first 4½ days was not accepted, because there were two administrations per day and ten in total.

Most candidates correctly calculated the increase in protein and only a few forgot to give units. The question should probably have used the command term calculate rather than state but few candidates only stated the values without carrying out the subtraction.

Answers to were very varied, with marks evenly spread between 0, 1, 2 and 3. The question was easier to answer if the instruction to give similarities as well as differences in compare questions was remembered. Quotation of numerical values rarely gains many marks in IB Biology exams. Some answers consisted only of this, but scored a maximum of one mark.

It was essential to remember that in evaluate questions implications and limitations are the focus. The experimental results for late administration of edaravone supported the hypothesis, but those for early administration did not. Candidates were expected to explain this partial support. Few were able to evaluate this. They seemed reluctant to say that it was only “partially correct” opting to say either correct or incorrect instead. Questions are never set to trick candidates but they need to be aware that much data is inconclusive and requires further testing of a hypothesis before it can be confirmed or rejected.

Candidates mostly found the last two parts of the question difficult. As this was an analyse question, the expected answers were interpretations of the data to reach conclusions. This involved more than merely describing or comparing the results. In particular, it was essential to separate the effects of PAN and edaravone. PAN caused the highest TBArs levels, indicating damage to membranes by oxidation. When edaravone was also administered, it prevented this damage. Many candidates talked about the combined effects of the two drugs, even though the stem of the question, on page 2, explained that edaravone is a proposed treatment for nephrotic syndrome, and PAN causes symptoms of the disease so can be used to simulate it. Only a minority of candidates coped well with part (g) and this was the only part of the question that aroused critical comments from teachers on G2 forms. It was again necessary to bear in mind statements in the stem of the question, especially that the presence of protein in urine is a symptom of nephrotic syndrome. Candidates were expected to recall how the structure of the glomerulus normally prevents proteins passing from blood in the glomerular capillaries to filtrate in the Bowman’s capsule. Candidates tended to score three marks or none, depending on whether they keyed in to the question correctly or not.

The examining team did not feel that this part was too hard. Partly because of (h) there was a better correlation between candidates’ performance in Question 1 and their overall standard in this paper, than in some other recent papers.