Zadanie 8, Paper 2, maj 2026, TZ1, Biologia IB HL
Wzorowane na: Biology HL Paper 2, May 2026, TZ1, pytanie 8. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
During exercise, oxygen delivery must meet increased demand in mammalian tissues.
(a) Outline the molecular structure of haemoglobin.
(b) Explain how the Bohr effect improves delivery of oxygen to tissues with a high respiration rate.
(c) Describe features of mature mammalian erythrocytes that adapt them for gas transport.
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Odpowiedź z klucza
(a) Haemoglobin is a compact globular protein. ✔
It contains four associated polypeptide chains, two alpha and two beta in adult haemoglobin. ✔
Each subunit carries a non-protein haem group. ✔
An iron ion is located within each haem group. ✔
(b) Rapidly respiring cells release more carbon dioxide. ✔
Dissolved CO₂ reacts with water to produce carbonic acid. ✔
Carbonic acid dissociates, releasing hydrogen ions and hydrogen carbonate. ✔
The increased hydrogen-ion concentration lowers pH. ✔
Hydrogen ions binding to haemoglobin favour its lower-affinity conformation. ✔
CO₂ association with haemoglobin can also favour oxygen release. ✔
Haemoglobin therefore has reduced affinity for oxygen in these conditions. ✔
At a given oxygen partial pressure, its saturation is lower than under lower-CO₂ conditions. ✔
The oxygen-dissociation curve is displaced to the right. ✔
More oxygen is unloaded near the cells with greater respiratory demand. ✔
A correctly labelled oxygen partial pressure/saturation graph can show the shift. ✔
Correctly distinguished low- and high-CO₂ curves on that graph support the comparison. ✔
(c) Mature erythrocytes have a biconcave shape. ✔
Their shape increases the surface available for gas diffusion. ✔
A high surface-area-to-volume ratio promotes rapid gas exchange. ✔
A flexible cell membrane permits passage through narrow capillaries. ✔
Abundant haemoglobin binds oxygen reversibly. ✔
Loss of the nucleus provides more space for haemoglobin. ✔
Schemat punktowania
(a) Award any 3 listed structural points; maximum 3 marks. (b) Award any 8 listed explanatory or valid graph points; maximum 8 marks. (c) Award any 4 listed adaptation points; maximum 4 marks. Quality: award 1 additional mark for a response across all three parts that is readily understandable, concise and largely free of repetition or irrelevant material. Judge this independently of content marks. Maximum 16 marks overall.