Use these model essay question responses to prepare for essay questions on your in class tests, as well as the IB Examination, Papers 2 & 3. These questions have appeared on recent IB examinations, exactly as shown below.
Following each question is the markscheme answer which was used to evaluate student answers on the examination paper.
1. Draw a simple diagram of the gas exchange system in humans. 5 marks
For a diagram of the whole gas exchange system, award 1 mark for each of the following structures
clearly drawn and labeled correctly.
For a diagram of an alveolus only, award 1 mark for each of the following structures clearly drawn
and labeled correctly.
2. Outline the difference between breathing and cell respiration. 1 mark
3. State the role of the alveoli. 1 mark
4. Define, with examples, the term homeostasis. 4 marks
5. Explain why ventilation rate varies with exercise. 6 marks
exercise increases metabolism; increases production of CO2 ; increased CO2 causes more acidity in blood / decrease pH; chemoreceptors in aorta / carotid artery detect change in pH; message to breathing centre / (Pons) medulla oblongata; message to diaphragm / intercostal muscles to increase breathing rate; increase ventilation rate for more gas exchange; long term effects of increased lung surface area / vital capacity; breathing rate decreases with time; [6 max]
6. Option H Further human physiology
A major requirement of the body is to eliminate carbon dioxide (CO2 ). In the body, carbon
dioxide exists in three forms: dissolved CO2, bound as the bicarbonate ion, and bound to proteins
(e.g. haemoglobin in red blood cells or plasma proteins). The relative contribution of each of these
forms to overall CO2 transport varies considerably depending on activity, as shown in the table
a) Calculate the percentage of CO2 found as bicarbonate ions in the plasma of venous blood at rest. 
(b) (i) Compare the changes in total CO2 content in the venous plasma due to exercise. 
increases by 0.63 mmol l−1 of blood / rises from 15.59 to 16.22 mmol l−
(ii) Identify which form of transport shows the greatest increase due to exercise. 
(c) Explain the pH differences shown in the data. 
CO2 makes the blood more acidic and the pH drops; pH of venous blood at rest has decreased compared to arterial blood; because the blood is carrying waste CO2 (from cellular respiration) back to lungs for removal; pH of venous blood after exercise has decreased compared to arterial blood; and dropped even further than venous blood at rest; because the blood is carrying more waste CO2 than normal due to exercise;
7. Explain the way the body acclimatizes to gas exchange at high altitudes. (Option H)
at high altitude there is a low partial pressure of O2 / less O2 in the air; red blood cell production increases to increase O2 transport; ventilation rate increases to increase gas exchange; people living permanently at high altitude have greater lung surface area; and larger vital capacity than people living at sea level; muscles produce more myoglobin to encourage O2 to diffuse into muscles / store O2 in muscles; hemoglobin dissociation curve shifts to the right encouraging O2 release into the tissues;
8. Option H – Further human physiology
Research into how the lungs perform during general anesthetics has increased because there are so many pulmonary complications during operations. It is believed that many inhaled anesthetics affect pulmonary epithelial permeability.
Pulmonary clearing is an indication of whether the alveolar-capillary barrier has been damaged. It can be measured as the rate at which radioactivity decreases in lungs after inhalation of a radioactive aerosol. The greater the clearing rate, the greater the damage to the alveolar-capillary barrier. Smoking and lung diseases (such as cancers and asthma) also significantly increase the clearing rate of radioactive aerosols.
In an experiment, doctors wanted to test the effect of inhaled anesthetics on the permeability between the alveoli and capillaries. Patients were tested by inhaling a radioactive aerosol one day before their operation and one hour after their operation.
Three groups of patients each received a different type of anesthetic.
Group 1: 1% halotane (inhaled anesthetic)
Group 2: 1.5% isoflurane (inhaled anesthetic)
Group 3: intravenous anesthetic (phentanyl and propofol)
(a) Compare the effect of each inhaled anesthetic on the permeability of the alveoli. 
(a) mean permeability for G1 (halotane) changes little / from 1.25 to 1.3 (! 0.1) % but
the mean permeability for G2 (isoflurane) increases / from 0.75 to 1.10 (! 0.1) %;
deviation for permeability of G1 changes little / 0.7 to 0.8 % but the deviation for
the permeability of G2 increases / 0.4 to 0.7 %;
(b) Using the data from the graphs, explain whether or not inhaled anesthetics are more
dangerous than intravenous anesthetics. 
(b) conflicting data;
G2 has difference but not G1, so cannot say inhaled anesthetics cause change;
G3 has more difference than G1 (although not significant), so inhaled less harmful
not enough data / all start at different mean / patients not all the same;
(c) Suggest one reason why asthmatic patients were not used in this experiment. 
(c) higher rate / more clearing / results not exact / greater risk to asthmatics / unethical;
9. Explain the oxygen dissociation curve for adult haemoglobin and how it is affected by the
Bohr shift.  (Option H)
Diagrams are acceptable provided they are adequately annotated. initial uptake of one oxygen molecule by haemoglobin facilitates the further uptake of oxygen molecules / haemoglobin has an increasing affinity for oxygen / and vice versa; shows how the saturation of haemoglobin with oxygen varies with partial pressure of oxygen / dissociation curve for (oxy)haemoglobin is S/sigmoid-shaped; low partial pressure of oxygen corresponds to the situation in the tissue; when partial pressure of oxygen is low, oxygen released; high partial pressure of oxygen corresponds to the situation in the lungs; when partial pressure of oxygen is high, oxygen taken up by haemoglobin; Bohr effect occurs when there is lower pH / increased carbon dioxide / increased lactic acid; shifts the curve to the right; oxygen more readily releases to (respiring) tissue;
10. Option H Further human physiology
The symptoms of asthma vary according to the time of year. A study was carried out in New York to determine if an increase in the amount of pollen in the air caused an increase in the number of asthma attacks. Over a period of 270 days, the number of people admitted to New York hospitals with asthma attacks was recorded. The graph below shows this data together with the pollen count.
(a) Identify the greatest number of hospital admissions in one day. 
(b) Describe how the numbers of hospital admissions changed over the period of study. 
(c) Evaluate whether the hypothesis that pollen in the air increases asthma attacks is supported
by the data.
(d) State one effect of asthma on the gaseous exchange system.
(d) inflammation of airways / bronchioconstriction / constriction of airways /
increased mucus secretion in airways / coughing / lack of breath
11. Explain how chemical changes in the blood alter the breathing rate during exercise.
lower blood pH / more acidic due to higher concentration CO2; action of carbonic anhydrase / release of H+ ions from H2CO3; detected (by chemosensors) in aorta / carotid artery; send signal to brain / respiratory centre; brain sends signals to diaphragm / intercostal muscles to increase rate; under involuntary control; rate of ventilation increases; 12. Health in humans depends upon the efficient functioning of all parts of the body, including the lungs and defence against disease. (a) (i) State the role of alveoli. (i) gas exchange / absorption of oxygen and removal of carbon dioxide; 
(ii) State one health problem that could affect the functioning of the alveoli. (ii) asthma / emphysema / tuberculosis / lung cancer / bronchitis / cystic fibrosis /
pneumonia;  (Reject smoking.) 13. H2. (a) (i) State the main problem with gas exchange at high altitudes. (i) Less (available) oxygen in air / blood / decreased partial pressure of oxygen; (ii) State one symptom that may appear due to this problem. (ii) ( for any of the following; [1 max].)
headache / dizziness;
difficulty in breathing; (b) Compare the adaptations to high altitude of an indigenous person with the short-term
adaptations that develop in a traveller to high altitude.
(b) ( for one of the following comparisons; [2 max].)
indigenous larger lungs / pulmonary surface / larger vital capacity;
traveller faster breathing / rate of ventilation;
traveller (starts) producing more red blood cells / erythrocytes while indigenous has more;
14. State how the supply of oxygen to respiring tissues is helped by:
(a) the diaphragm.
(a) helps inflate the lungs when it contracts / increases thorax volume;
(b) myoglobin. 
(b) stores oxygen in the muscles;
(c) the Bohr shift. 
(c) causes more oxygen to be released in tissues with high CO2 levels;
15. List two ways carbon dioxide is carried by the blood. 
as dissolved CO2;
as hydrogencarbonate / bicarbonate / HCO3- ions;
as carbamino compounds / bound to haemoglobin;