Living on the roof of the world
312 words over 29 numbered lines, then 6 parts worth 12 marks (Modular Unit 2 (4WBI2) style, 12–13 marks). Read the article, answer each part, then open its mark scheme and set your mark.
Illustrative article written for Scholar Lab, not a Pearson text. The biology is real; the studies, people and figures are invented or rounded for practice.
Living on the roof of the world
At the top of a high mountain, the air contains the same proportion of
oxygen as the air at sea level, but the air is much less dense. Each
breath therefore contains fewer oxygen molecules. Climbers who arrive
quickly from sea level often feel breathless and tired, and some
develop headaches and sickness.
In the lungs, oxygen diffuses from the air in the alveoli into the
blood in the capillaries. At high altitude the concentration of oxygen
in the alveoli is lower, so the concentration gradient is less steep
and less oxygen enters the blood each minute. Muscle cells then
receive less oxygen for aerobic respiration.
Oxygen is carried by red blood cells. These cells have a biconcave
disc shape, no nucleus, and are packed with haemoglobin, which
combines with oxygen in the lungs and releases it in the tissues.
Within a few weeks at high altitude, the body makes more red blood
cells, and the concentration of haemoglobin in the blood rises.
Figure 1 shows illustrative blood tests from three groups of adults:
people living at sea level, the same people after three weeks at a
mountain research station, and people whose families have lived at
high altitude for many generations.
Having more red blood cells is not always helpful. The blood becomes
thicker, so the heart has to work harder to pump it around the body,
and blood clots may form more easily. Some groups of people who have
lived at high altitude for thousands of years have a different
solution: they breathe faster and deeper, and have wider blood
vessels, but have a similar number of red blood cells to people living
at sea level.
Some athletes now train at high altitude for several weeks before
important races held at sea level, hoping that the extra red blood
cells will still be there on the day of the race.
Figure 1 Blood test results from three groups of adults
| Group | Red blood cells / millions per mm³ | Haemoglobin / g per 100 cm³ |
|---|---|---|
| Sea-level residents | 5.0 | 14.5 |
| Same people after 3 weeks at altitude | 5.5 | 16.0 |
| Long-term high-altitude residents | 6.0 | 17.5 |
Read the article and study the figure. Use the information in the article and your own knowledge to answer the questions. The lines in brackets show where to look; select them to highlight the text.
Use the information in the article and your own knowledge to answer the questions. The lines in brackets show you where to look; select them to highlight the text.
State what is meant by the term diffusion.
(1)Describe two ways in which red blood cells are adapted to carry oxygen.
(2)Explain why climbers who arrive quickly at high altitude feel tired.
(3)Use Figure 1 to calculate the percentage increase in haemoglobin concentration after three weeks at altitude. Give your answer to one decimal place.
(2)Explain why having a very large number of red blood cells may be harmful.
(2)Suggest how training at high altitude could help an athlete in a race held at sea level.
(2)Total for this question: 12 marks
0 / 12 marks · 0 of 6 parts rated
Open each mark scheme, compare it with your answer and set your mark. Only your marks are kept, in this browser on this device; your written answers are never saved. Green is full marks, amber is half or more, red is under half.