Question

how do cholesterol molecules stabilize the cell membrane?
they hold phospholipids together when temperatures are high
they make new phospholipids when the membrane is damaged
they cause phospholipids to move in particular directions when temperatures are too hot
they act as spacers between phospholipids when temperatures are low

Explanation:

Cholesterol has a dual - role in the cell membrane. At high temperatures, it restricts the movement of phospholipids (prevents them from moving too freely). At low temperatures, it acts as a spacer between phospholipids, preventing them from packing too tightly.

• Option 1: Cholesterol does not "hold" phospholipids together at high temperatures in the sense described. At high temperatures, it reduces the fluidity by interacting with phospholipids (not just holding them).
• Option 2: Cholesterol does not synthesize new phospholipids. Phospholipids are synthesized through other biochemical pathways (e.g., in the endoplasmic reticulum).
• Option 3: Cholesterol does not direct the movement of phospholipids in a particular direction. It mainly affects their packing and fluidity.
• Option 4: At low temperatures, phospholipids tend to pack closely together, which can make the membrane rigid. Cholesterol acts as a spacer, maintaining some fluidity.

Answer:

they act as spacers between phospholipids when temperatures are low