Final answer:
As haemoglobin saturation decreases, the affinity of haemoglobin for oxygen also decreases. A rightward shift in the oxygen dissociation curve indicates this decrease in affinity, which can be caused by increased carbon dioxide, lower pH, or higher body temperatures.
Step-by-step explanation:
The question is asking what happens to the haemoglobin saturation when it decreases. As haemoglobin saturation decreases, the affinity of haemoglobin for oxygen also decreases. This relation between oxygen saturation and affinity is depicted in the oxygen dissociation curve. When the curve shifts to the right, it indicates a decreased affinity for oxygen, which occurs in response to conditions such as increased carbon dioxide levels, decreased pH, or heightened body temperature. Conversely, a shift to the left would indicate an increased affinity.
Among the choices given, option C is correct: As haemoglobin saturation decreases, the affinity of haemoglobin for oxygen decreases. Conditions that can cause a rightward shift in the oxygen dissociation curve, leading to reduced haemoglobin affinity for oxygen, include an increase in carbon dioxide in the blood or a rise in body temperature, both of which are associated with increased physiological activity or pathology, as seen in disorders like sickle cell anaemia and thalassemia.