Question

estion 14

Which of the following factors would decrease (slow down) diffusion rates?

		greater membrane surface area
		higher temperature
		higher molecular weight
		steep gradient
		None of the above

Answer 1

Question 14. Diffusion is a physical process in which the ions or molecules are distributed from higher concentration region to lower concentration region along with the concentration gradient. The rate of diffusion is dependent on several factors.

The rate of diffusion is decreased (slowed down) when the molecular weight of the molecules in the solution are higher. The rate of diffusion is inversely proportional to the square root of molecular weight of the molecules in that solution. This is the law of Graham, it states that when the molecular weight of molecules are higher then the diffusion rate of that molecules are decreased. So higher molecular weight (option 3) is the correct option for the above question.

Greater membrane surface area wouldn't decrease the diffusion rate of molecules. The greater surface area of a molecule increases the diffusion rate in the solution. Surface area to volume ratio is a important factor for the diffusion. Greater surface area increases the ratio and increase diffusion rate. So greater membrane surface area is not the correct option (option1) for decreasing the diffusion rate of molecules.

High temperature (option2) is the incorrect option for the above question because, in increasing temperature the velocity of the molecules in a solution is increased this increase in velocity also enhance the diffusion rate of the molecules. So, temperature of the solution should be lower for decreasing the diffusion rate of the molecules. So high temperature is a incorrect option.

Steep gradient (option 4) for decreasing the diffusion rate of the molecules is a incorrect option because, Fick's law states that diffusion rate is proportional to the concentration gradient. So bigger concentration difference between two area, there is more steep concentration gradient and this will enhance the diffusion rate and molecules will move faster from higher concentration to lower concentration region. So steep gradient increases the diffusion rate. So the steep gradient is not a correct option fir decreasing the diffusion rate.

• Higher molecular weight is the only option in the above question which can decrease the diffusion rate.