Question 17N.2.HL.TZ0.g
| Date | November 2017 | Marks available | [Maximum mark: 2] | Reference code | 17N.2.HL.TZ0.g |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Discuss | Question number | g | Adapted from | N/A |
Hypoxia is a condition in which tissues of the body are deprived of an adequate oxygen supply. A study was carried out in rats to examine the effects of continuing hypoxia on the structure of the diaphragm, and to determine whether nitric oxide is implicated in adaptation of the diaphragm to hypoxia. The diaphragm helps to supply oxygen to tissues and organs in the body by ventilating the lungs.
A group of 36 adult male rats were kept for 6 weeks in low oxygen while 36 adult male rats were kept in normal oxygen levels.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
The graph shows the effect of hypoxia on the endurance of rats’ diaphragm muscle after 6 weeks. Endurance is the change in force measured as a percentage of the initial force.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
The sodium–potassium pump plays a role in muscle activity. Nitric oxide may have a role in the recovery of hypoxic muscles. The production of nitric oxide can be blocked with an inhibitor of the enzyme nitric oxide synthase. The graph shows the concentration of sodium–potassium pumps in the diaphragm of control and hypoxic rats without and with nitric oxide synthase inhibitor.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
Skeletal muscle contractions can take two different forms: if they are stimulated by a single action potential they take the form of a twitch and if they are stimulated by a series of action potentials the contraction is longer lasting (tetanic). The table shows the effects of hypoxia on the force of twitch and peak tetanic contraction in the diaphragm.
[Source: Reproduced with permission of the © ERS 2011. European Respiratory Journal June 2011, 37 (6) 1474–1481; DOI: 10.1183/09031936.00079810]
Discuss the advantages and disadvantages of using rats as models in this investigation.
[2]
Advantages:
a. small size
OR
easy to look after in research labs
b. short lifespan
OR
study can extend over several generations
c. can be killed «to get experimental results» if benefits of research justify it
d. «mammalian» so similarities with humans
e. fewer ethical objections than if humans are used/not ethical to subject humans to hypoxia/does not cause harm to humans
Accept any one of the advantages
Disadvantages:
f. ethical objections
OR
wrong to cause suffering to animals/rats
g. rat physiology/anatomy not same as human
Accept any one of the disadvantages
[Max 2 Marks]
