How does the structure of hemoglobin change in low oxygen conditions?

In low oxygen conditions, hemoglobin transitions to a tense state, also known as the T state. This state has a lower affinity for oxygen compared to the relaxed state (R state). In the T state, the hemoglobin molecule is less dynamic and more compact, allowing it to release oxygen more effectively to the tissues that need it.

When oxygen levels drop, hemoglobin's alteration to the T state enhances its ability to deliver oxygen where it is most needed, such as in actively metabolizing tissues. This conformational change facilitates the release of oxygen from hemoglobin, making the protein particularly efficient in environments where oxygen is scarce.

The other choices do not accurately describe the behavior of hemoglobin under low oxygen conditions. The rigidity of hemoglobin (first option) is not a characteristic that facilitates oxygen release, while a dome shape (second option) is not an accurate description of hemoglobin's structural changes. Additionally, binding more oxygen (fourth option) is contrary to the nature of how hemoglobin operates under low oxygen conditions. Thus, the transition to the tense state is key for oxygen delivery in low oxygen scenarios.