The rate of diffusion through a semipermeable membrane will be lowest when which of the

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Trpko B

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following is (are) tru? I. Concentration gradients are steep.
II. Temperatures are low.
III. Solutes are small molecules.

a. I only
b. II only
c. I and III
d. II and III
e. I, II and III
 
The answer is B because of the following reasons:

When the concentration gradients are steep there is one side with a lot of solute. The solute molecules pump into one another frequently and therefore are more likely to be "launched" through the membrane.

When the temperature is low, the solute particles move slowly (this is basic ke = 1/2mv^2 where ke, which can be measured in temperature, is directly proportional to the square of the velocity). Because the particles are moving slowly, they bump into each other less often and therefore do not pass through the membrane as frequently.

Lastly, when solutes are small molecules they pass through the membranes smaller holes more easily.
 
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