On the graph, the curve labeled No Cholesterol shows the fluidity of the fatty acids of a phospholipid bilayer as a function of temperature. The curve labeled +
Cholesterol shows the fluidity in the presence of cholesterol. The transition temperature, Tm,
is the temperature at which membranes transition between a rigid state and a more fluid state

What is the effect of cholesterol in the cell membrane?

Question

On the graph, the curve labeled No Cholesterol shows the fluidity of the fatty acids of a phospholipid bilayer as a function of temperature. The curve labeled +
 Cholesterol shows the fluidity in the presence of cholesterol. The transition temperature, Tm,
 is the temperature at which membranes transition between a rigid state and a more fluid state

What is the effect of cholesterol in the cell membrane?

BlackTom AI · Accepted Answer

The question asks about the effect of cholesterol on the cell membrane, as depicted by the No Cholesterol (pink) and + Cholesterol (blue) curves showing membrane fluidity versus temperature, with Tm indicating the transition temperature.
Option 1: 'Cholesterol regulates membrane fluidity over a wide temperature range.' This is consistent with the typical role of cholesterol: it broadens the phase transition, preventing membranes from becoming too rigid at low temperatures and too fluid at high temperatures. By flattening and broadening the transition curve, cholesterol maintains a more stable fluidity across temperatures, which matches the depiction where the presence of cholesterol (blue curve) shifts and smooths the transition relative to the no-cholesterol condition.
Option 2: 'Cholesterol facilitates an abrupt transition from a less fluid state to a more fluid state.' This contradicts the graph and the known function of cholesterol. Cholesterol tends to stabilize membranes and reduce the sharpness of the transition, not promote a sharp, abrupt shift from rigid to fluid; in the graph, the + Cholesterol curve does not show an abrupt jump compared to No Cholesterol.
Option 3: 'Cholesterol slows the passage of polar molecules over a wide temperature range.' While cholesterol does influence permeability to some extent, the question and graph focus on overall membrane fluidity rather than direct permeability of polar molecules. The statement is not the primary takeaway from the curves and misstates the observed effect on fluidity across temperatures.
Option 4: 'Cholesterol increases membrane fluidity at all temperatures.' This is incorrect because cholesterol does not uniformly increase fluidity; at low temperatures it prevents tight packing (increasing fluidity compared to overly rigid membranes) and at high temperatures it reduces excessive fluidity, acting as a buffer. The graph shows cholesterol changing the fluidity profile rather than simply increasing it across the board.
In summary, the most accurate interpretation given the curves is that cholesterol moderates or regulates membrane fluidity across a wide temperature range, preventing extreme rigidity or excessive fluidity, which aligns with option 1.

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