[单选题]
The diagram shows a
go:4j.w*0v:ipqbk(e2 w oqle7h zqj8 :ytbbyl:5 fcwhs zs:5 54- luwpolar bear (Ursus maritimus), which is native to the Arctic. Which statement about the composit
4:t:y:whbu5- lf5wbl yz c5ss ion of its plasma membranes is correct?
A. They contain a higher percentage of saturated fatty acids compared to unsaturated fatty acids.
B. They contain an equal percentage of saturated and unsaturated fatty acids.
C. They contain a higher percentage of unsaturated fatty acids compared to saturated fatty acids.
D. They only contain unsaturated fatty acids.
参考答案:
C
本题详细解析:
Unsaturated fatty acids have one or more double bonds in their hydrocarbon chains, creating kinks and preventing the fatty acids from packing tightly. This means that unsaturated fatty acids help to maintain membrane fluidity at lower temperatures, preventing the membrane from becoming too rigid and allowing cells to function properly even in the cold. However, the membrane does not just contain unsaturated fatty acids (Choice D), as a combination of saturated and unsaturated fatty acids contributes to the overall properties of the plasma membrane, such as permeability, stability, and responsiveness to environmental changes. Choice C is therefore correct.
Saturated fatty acids have no double bonds between the carbon atoms in their hydrocarbon chains, making them relatively straight and able to pack closely together. Having a high percentage of saturated fatty acids in the membrane (Choice A) would result in a more rigid and less fluid membrane. Choice B is incorrect as plasma membranes in polar bears do not have an equal percentage of saturated and unsaturated fatty acids as this, also, would not allow plasma membranes to maintain the required fluidity.
