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(a) The water flea, Daphnia pulex, is a small invertebrate animal that lives in ponds - Scottish Highers Human Biology - Question 11 - 2019
Question 11
(a) The water flea, Daphnia pulex, is a small invertebrate animal that lives in ponds. Water fleas can be used as model organisms to investigate the effect of chemi... show full transcript
Worked Solution & Example Answer:(a) The water flea, Daphnia pulex, is a small invertebrate animal that lives in ponds - Scottish Highers Human Biology - Question 11 - 2019
Step 1
Suggest why the student left the water flea in the solution for 5 minutes before videoing its heart rate.
Answer
The student left the water flea in the solution for 5 minutes to allow the water flea to acclimatize to the new conditions. This ensures that the heart rate stabilizes and accurately reflects the effects of the caffeine concentration.
Step 2
Suggest why the student videoed the water flea rather than simply counting its heart beat at the time.
Answer
Videoing the water flea allows for a more accurate and reliable recording of the heart rate. It also makes it easier to play back the video to count the heartbeats, minimizing potential counting errors in real time.
Step 3
Use data from the table to describe the changes that occur in the heart rate as the caffeine concentration increases.
Answer
As the caffeine concentration increases from 0 g/l to 0.8 g/l, the heart rate of the water flea rises steadily from 135 bpm to 270 bpm. Specifically, it increases by 50 bpm after each increase in caffeine concentration until it reaches 0.8 g/l, where it levels off at 270 bpm. At concentrations above 0.8 g/l, there is no further increase in heart rate.
Step 4
State how the reliability of the results from this investigation could be improved.
Answer
To improve the reliability of the results, the experiment could be repeated with more water fleas to obtain an average heart rate. This would account for any variability between individual water fleas and strengthen the findings.
Step 5
In humans, describe how the autonomic nervous system increases the heart rate.
Answer
The autonomic nervous system increases the heart rate through the following mechanisms:
- The medulla controls the autonomic nervous system, particularly the sympathetic branch that affects heart rate.
- The sino-atrial node (SAN) generates signals that spread through the heart, affecting the atria and the atrio-ventricular node (AVN).
- Activation of the sympathetic nerves leads to the release of noradrenaline.
- Noradrenaline acts on the heart to increase its rate, enhancing cardiac output.