Question 17N.2.HL.TZ0.01f
| Date | November 2017 | Marks available | [Maximum mark: 3] | Reference code | 17N.2.HL.TZ0.01f |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Evaluate | Question number | f | 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]
Using all relevant data in the question, evaluate the effectiveness of the rats’ adaptation to hypoxia.
[3]
a. not effective because body mass lost
b. effective because body mass still increases/rats still grow
c. not effective because contractions/force exerted by diaphragm decreases
d. effective because more sodium-potassium pumps so more/faster rate of diaphragm/muscle contractions
e. effective because endurance of diaphragm increases
f. effective because mass of right ventricle increases
g. effective because erythrocyte percentage increases
For each marking point the candidate must make it clear whether they are arguing for adaptation being effective or not. This can be done by giving the physiological benefit of a change, for example greater mass of right ventricle so more blood pumped.
[Max 3 Marks]
