Question

Which of the following statements is/are true for a system in which a cation (an ion that is positively charged; e.g., Na+) is freely permeable?

Pick all true statements

a. In the absence of a chemical gradient, the net diffusion of a cation will be from an area of positive charge to an area of negative charge.

b. In the absence of a chemical gradient, the net diffusion of a cation will be from an area of negative charge to an area of positive charge.

c. In the absence of an electrical gradient, the net diffusion of a cation will be from an area of high concentration to an area of low concentration.

d. The net diffusion rate for a cation will be maximal when it is moving from an area of high concentration to an area of low concentration, and from an area of positive charge to an area of negative charge.

e. The net diffusion rate for a cation will be maximal when it is moving from an area of high concentration to an area of low concentration, and from an area of negative charge to an area of positive charge.

f. It is possible for the net diffusion rate of a cation to be zero even in the presence of a concentration gradient.

g. It is possible for the net diffusion rate of a cation to be zero even in the presence of an electrical gradient.

Answer 1

For a cation freely permeable across a membrane, net diffusion occurs from positive to negative areas in the absence of a chemical gradient, from high to low concentration in the absence of an electrical gradient, and the diffusion rate can be zero if gradients counterbalance each other.

Step-by-step explanation:

For a system in which a cation is freely permeable:

• a. In the absence of a chemical gradient, the net diffusion of a cation will be from an area of positive charge to an area of negative charge, following the electrical gradient.
• c. In the absence of an electrical gradient, the net diffusion of a cation will be from an area of high concentration to an area of low concentration, following the concentration gradient.
• f. It is possible for the net diffusion rate of a cation to be zero even in the presence of a concentration gradient. This can occur when the electrical gradient counterbalances the concentration gradient, leading to electrochemical equilibrium.

The statements b, d, e, and g are not true because they either depict incorrect movement based on charge or imply scenarios that do not apply to the diffusion of ions across a concentration or electrical gradient.