This diagram is of an alveolus and a nearby blood capillary in a human lung. Air in the alveolus has a higher concentration of oxygen than the blood arrivin...
Question 1 Report
This diagram is of an alveolus and a nearby blood capillary in a human lung. Air in the alveolus has a higher concentration of oxygen than the blood arriving at the capillary. The thin walls allow rapid exchange. Red blood cells carry oxygen away from the lung to body cells, including cells in a leaf-like network of muscles around the chest.
(a) What process moves oxygen from the alveolus into the blood? [1]
(b) Give one feature of an alveolus that makes gas exchange rapid. [1]
(c) Describe what happens to the oxygen concentration in the blood as it flows past the alveolus. [2]
Fig. 1 shows a microscope field from a culture of a single-celled organism living in pond water. The organism was placed in water containing glucose. A researcher added methylene blue, which is blue when oxygen is present and becomes colourless when oxygen is used. Table 1 shows the time taken for the dye to become colourless at different temperatures.
| Temperature / degrees C | Time for dye to become colourless / min |
|---|---|
| 12 | 18 |
| 22 | 8 |
| 32 | 5 |
(a) Describe the result as temperature increases from 12 to 32 degrees C. [1]
(b) What does a shorter time show about the rate of respiration? [1]
(c) Give two variables that should be kept the same in each sample. [2]
(d) Explain why the researcher should repeat each temperature test. [1]
Answer Details
Labelled answer diagram:
Alveolus and capillary
(a) Oxygen moves from an alveolus into the blood by diffusion. [1]
(b) An alveolus has a wall one cell thick, giving a short diffusion distance. A large surface area, moist lining or good blood supply are also acceptable. [1]
(c) Oxygen diffuses into the blood as it flows past the alveolus, so the oxygen concentration in the blood increases. [2]
Single-celled organism investigation
(a) As temperature increases from 12°C to 32°C, the time for the dye to become colourless decreases from 18 minutes to 5 minutes. [1]
(b) A shorter time means oxygen is used more quickly, so respiration is faster. [1]
(c) Two variables to keep the same are the number of organisms and the glucose concentration. Water volume, and the volume or concentration of methylene blue, are also acceptable. [2]
(d) Repeating each test helps identify anomalous results, allows a mean to be calculated and improves reliability. [1]
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