Explanation:
When temperature decreases, the oxyhemoglobin (HbO2) dissociation curve becomes more steep.

Understanding the Oxy-Hb curve:
The oxyhemoglobin dissociation curve represents the relationship between the partial pressure of oxygen (PO2) and the saturation of hemoglobin with oxygen (SO2). It shows how readily hemoglobin binds to or releases oxygen molecules in response to changes in the partial pressure of oxygen.

Effect of temperature on Oxy-Hb curve:
Temperature affects the affinity of hemoglobin for oxygen. When the temperature decreases, the oxyhemoglobin dissociation curve shifts to the right, indicating a decreased affinity of hemoglobin for oxygen. This means that at any given partial pressure of oxygen, hemoglobin will release oxygen more readily.

Explanation of the answer:
When the temperature decreases, the oxyhemoglobin dissociation curve becomes more steep. This means that for a given decrease in partial pressure of oxygen, the amount of oxygen released by hemoglobin is greater compared to when the temperature is higher. This is because the decrease in temperature causes hemoglobin to have a lower affinity for oxygen, allowing it to release oxygen more readily.

Reason behind the steepening of the curve:
The steepening of the oxyhemoglobin dissociation curve with a decrease in temperature can be explained by the effect of temperature on the conformational changes in hemoglobin. Hemoglobin exists in two forms: the relaxed (R) form with high oxygen affinity and the tense (T) form with low oxygen affinity. When oxygen binds to hemoglobin, it stabilizes the R form, making it easier for other oxygen molecules to bind. On the other hand, when oxygen is released, it stabilizes the T form, making it easier for other oxygen molecules to be released.

A decrease in temperature stabilizes the T form of hemoglobin, reducing its affinity for oxygen and promoting the release of oxygen. This results in a more pronounced decrease in oxygen saturation for a given decrease in partial pressure of oxygen, leading to a steeper oxyhemoglobin dissociation curve.

In conclusion, when the temperature decreases, the oxyhemoglobin dissociation curve becomes more steep due to the decreased affinity of hemoglobin for oxygen, causing it to release oxygen more readily at any given partial pressure of oxygen.