Final answer:
Cholesterol rings in the phospholipid membrane help to regulate the membrane's fluidity and rigidity, acting as a temperature buffer and contributing to the membrane's shape and stability.
Step-by-step explanation:
Cholesterol rings in the phospholipid membrane help regulate the fluidity and rigidity of the membrane. Animals have an additional membrane constituent that assists in maintaining fluidity. Cholesterol, interspersed between phospholipids, functions as a buffer against the effects of temperature changes. It prevents lower temperatures from inhibiting fluidity and high temperatures from increasing fluidity excessively. Therefore, cholesterol allows the plasma membrane to maintain an appropriate level of fluidity across a range of temperatures, which is crucial for cellular function and structural integrity.
Additionally, cholesterol plays a role in organizing lipid rafts, which are clusters of transmembrane proteins that are critical in cellular processes. In the cell membrane, it works as antifreeze and is more abundant in animals that live in cold climates. Alongside other molecules such as embedded proteins and carbohydrates, cholesterol helps the plasma membrane keep its shape, contributing to the overall stability and functionality of the cell.