Free Transport in mammals questions for AS Level Biology (9700), part of Transport & disease. Each question has the answer and the marking points an examiner would look for.
Generate a full Transport in Mammals worksheet →All Transport & disease questionsHaemoglobin and the Bohr shift.
Which row describes the effect of increased carbon dioxide concentration?
| affinity of haemoglobin for oxygen | oxygen dissociation curve | oxygen released to respiring tissue | |
|---|---|---|---|
| A | decreases | shifts to the left | increases |
| B | increases | shifts to the right | increases |
| C | increases | shifts to the left | decreases |
| D | decreases | shifts to the right | increases |
Answer: D
Which term is described by this statement?
“Decreased haemoglobin affinity for oxygen at high carbon dioxide concentration.”
Answer: C
The cardiac cycle is controlled by the sinoatrial node.
1 The atrioventricular node delays the impulse so the atria empty before the ventricles contract.
2 The heart muscle is myogenic.
3 The atrioventricular valves are open during ventricular systole.
Which statements are correct?
Answer: B
The percentage saturation of haemoglobin at different partial pressures of oxygen is shown.
| pO2 / kPa | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|
| % saturation | 16 | 57 | 81 | 90 | 95 |
Explain the S-shape of the oxygen dissociation curve.
Calculate the percentage of oxygen released when blood moves from lungs (pO2 = 10 kPa) to tissues at pO2 = 4 kPa.
Explain how carbon dioxide from respiring tissues increases oxygen release (the Bohr shift).
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | first O2 binds with difficulty; binding changes shape of haemoglobin (cooperative binding) making next easier; last site harder to fill first oxygen binds less readily B1 conformational change increases affinity B1 levels off as saturation approached B1 | 3 |
| (b) | 38 difference in saturation C1 38 A1 | 2 |
| (c) | CO2 + H2O → H2CO3 by carbonic anhydrase; dissociates to H+ and HCO3−; H+ binds haemoglobin forming HHb; lowers affinity, more O2 released; curve shifts right carbonic anhydrase forms carbonic acid B1 H+ released B1 H+ combines with haemoglobin (haemoglobinic acid) B1 lower affinity, curve shifts right B1 | 4 |
This question is about transport of oxygen and carbon dioxide in mammals.
Describe the shape of the oxygen dissociation curve for adult haemoglobin and explain it.
Describe how most carbon dioxide is transported in the blood.
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin. Explain why this is important.
State the roles of the sinoatrial node and atrioventricular node in the cardiac cycle.
Explain why the wall of the left ventricle is thicker than that of the right ventricle.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | S-shaped (sigmoid); first O₂ binds with difficulty; cooperative binding changes shape; later O₂ binds easily, saturates sigmoid / S-shaped B1 binding of the first O₂ is difficult B1 it changes the shape of haemoglobin (cooperative binding) so the next O₂ molecules bind more easily B1 the curve levels off near full saturation B1 | 4 |
| (b) | enters red cell; carbonic anhydrase forms carbonic acid; dissociates to H⁺ and HCO₃⁻; HCO₃⁻ diffuses into plasma, chloride shift Any 3 of: CO₂ diffuses into red blood cells; carbonic anhydrase catalyses CO₂ + H₂O → H₂CO₃; which dissociates into H⁺ and HCO₃⁻; hydrogencarbonate ions diffuse into the plasma and chloride ions move in (chloride shift) B3 | 3 |
| (c) | fetal Hb can load oxygen from mother’s blood at the placenta, where pO₂ is low at the placenta the partial pressure of oxygen is low B1 fetal haemoglobin can still become saturated and take oxygen from the mother’s haemoglobin B1 | 2 |
| (d) | SAN initiates wave of excitation across atria; AVN delays, then passes down Purkyne fibres to ventricle apex SAN (pacemaker) sends a wave of excitation across the atria causing atrial systole B1 the AVN delays the impulse so atria empty first B1 the impulse then passes down the Purkyne tissue to the ventricle base so ventricles contract from the apex upwards B1 | 3 |
| (e) | pumps blood to the whole body at higher pressure it pumps blood through the systemic circulation at higher pressure B1 | 1 |
The cardiac cycle is controlled by the heart’s own conducting tissue.
Describe the roles of the SAN, AVN and Purkyne tissue.
| Part | Answer and marking points | Marks |
|---|---|---|
| SAN pacemaker; AVN delay; Purkyne to apex SAN initiates wave of excitation (pacemaker) B1 atria contract B1 AVN delays impulse so atria empty B1 Purkyne tissue carries impulse to apex so ventricles contract from base upwards B1 | 4 |
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