Final answer:
Cholesterol makes the cell membrane more rigid or less flexible at lower temperatures by filling in the gaps between phospholipids.
Step-by-step explanation:
Cholesterol plays a role in controlling the fluidity of the cell membrane. At lower temperatures, cholesterol makes the membrane more rigid or less flexible. This is because cholesterol fills in the gaps between phospholipids, reducing the amount of space and mobility in the membrane. As a result, the membrane becomes less fluid and less flexible.