Note: Questions 1 to 5 and 11 can be attempted by Standard level pupils. Higher level pupils can attempt all the questions. Standard: 23 marks, Higher: 43 marks.
The diving reflex occurs in marine mammals. This causes the heart rate to slow down when they are diving. In order to observe whether the condition exists in humans, 20 free divers (divers who do not use breathing equipment) were subjected to two conditions:
Their pulse was measured every 10 seconds and converted to bpm (beats per minute). The data, calculated as means for all 20 participants in each condition is shown below. The error bars estimate the uncertainty of the method of timing and counting the pulses rates (estimated at 5%).
I. a negative correlation/ heart rate decreases with time (of immersion) b plateaus at 25 seconds (2 marks)
II. carbon dioxide concentration in blood/stress (1 mark)
III. a supported b heart rate increases with apnea only c decreases with immersion in cold water c head when immersed prevents breathing but the response is different (3 max) d not supported e effect of cold water alone not tested/warm water not tested/only one temperature tested/insufficient trials (2 max) (4 max total)(Total 4 marks but reason must match acceptance of hypothesis)
IV. carbon dioxide from muscles remains in muscle/not transported to brain/conservation of oxygen/energy (1 mark)
When replying to the command term “suggest” ensure that you use your knowledge rather than guess.
See subtopic D4.
Philpot Education
Philpot Education