| Date | November 2015 | Marks available | 1 | Reference code | 15N.3.HL.TZ0.1 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Calculate | Question number | 1 | Adapted from | N/A |
Question
Researchers investigating human evolution recorded energy use for the brain, gastrointestinal tract (gut), liver, kidneys and heart as a percentage of total energy used in the human body. They found that these organs use around 70 % of the body’s energy although they account for only about 7 % of body mass. They also compared the mass of each of these organs in humans with other modern primates, each with a body mass of 65 kg as shown in the bar chart.
Calculate the percentage of the total body mass made up by the human brain.
Compare the mass of human organs with the mass of other primate organs.
Using information from the table and the graph, identify the human organ which uses the greatest amount of energy per kilogram of body tissue.
Explain the differences between the organ size of humans and other primates in terms of trends in human evolution and their causes.
Markscheme
a. total organ mass (approximately) same for both;
b. very little difference in mass in heart/kidney/liver;
c. human brain has greater mass than the primate brain;
d. human gut has lower mass than the primate gut;
heart
a. brain size increased during hominid evolution / OWTTE;
b. change in diet from mostly vegetarian to more protein-rich/meat eating diets;
c. eating meat/protein allows larger brain growth / change in diet corresponds to the start of increase in hominid brain size;
d. larger brains require more energy;
e. larger gut necessary for plant material digestion;
f. smaller gut is sufficient for meat/cooked food;
Examiners report
The majority of candidates could interpret the data correctly, although there were some erroneous calculations and identifications of liver instead of heart as the organ using the greatest amount of energy per kilogram of body tissue (due to calculation issues). Most candidates displayed some knowledge when explaining the different organ sizes, but their understanding of cause and effect was sometimes not that clear.
The majority of candidates could interpret the data correctly, although there were some erroneous calculations and identifications of liver instead of heart as the organ using the greatest amount of energy per kilogram of body tissue (due to calculation issues). Most candidates displayed some knowledge when explaining the different organ sizes, but their understanding of cause and effect was sometimes not that clear.
The majority of candidates could interpret the data correctly, although there were some erroneous calculations and identifications of liver instead of heart as the organ using the greatest amount of energy per kilogram of body tissue (due to calculation issues). Most candidates displayed some knowledge when explaining the different organ sizes, but their understanding of cause and effect was sometimes not that clear.
The majority of candidates could interpret the data correctly, although there were some erroneous calculations and identifications of liver instead of heart as the organ using the greatest amount of energy per kilogram of body tissue (due to calculation issues). Most candidates displayed some knowledge when explaining the different organ sizes, but their understanding of cause and effect was sometimes not that clear.
