Final answer:
The plasma membrane of the Mojave Desert animal is likely to have a higher cholesterol content to maintain membrane stability in high temperatures, whereas the Mediterranean coast animal's membrane may be more fluid to support cell function in a milder climate.
Step-by-step explanation:
The composition of plasma membranes is influenced by the environment in which an organism lives. For the animal from the Mojave Desert, its cell membranes will have adaptations for a high-temperature environment, likely having a higher cholesterol content to reduce membrane fluidity and prevent it from becoming too permeable in the heat. In contrast, the animal from the Mediterranean coast may have cell membranes with a higher fluidity due to differences in environmental temperatures.
When compared to each other, the Mediterranean coast animal is expected to have more fluid plasma membranes to facilitate better function in its relatively milder environment. Conversely, the Mojave Desert mammal likely needs its plasma membranes to be more rigid to withstand extreme temperatures, thus having a higher concentration of cholesterol to achieve this effect is probable.
The fluid mosaic model helps explain why the plasma membrane's composition would vary between these animals. Both temperature and the saturation level of the membrane's phospholipid tail's affect fluidity. Unsaturated fatty acids make the plasma membrane more fluid, while cholesterol decreases fluidity, compensating for high-temperature environments.