Why must active transport of molecules across plasma membranes function continuously? a. Diffusion cannot occur in certain cells. b. Diffusion is constantly moving solutes in opposite directions. c. Facilitated diffusion works in the same direction as active transport. d. Not all membranes are amphiphilic.
The correct answer and explanation is:
The correct answer is b. Diffusion is constantly moving solutes in opposite directions.
Active transport across plasma membranes is necessary to maintain the proper concentrations of ions and other molecules inside and outside the cell, despite the fact that diffusion continually moves solutes in opposite directions. Diffusion is a passive process where molecules move from areas of higher concentration to areas of lower concentration. However, this movement is random and does not support the maintenance of specific concentrations of molecules that cells require for their functions.
In certain cases, diffusion can result in substances moving in opposite directions across the membrane. For example, sodium ions (Na⁺) might diffuse into the cell while potassium ions (K⁺) diffuse out, but this doesn’t maintain the concentrations required for cellular functions. Active transport is an energy-requiring process that moves molecules against their concentration gradients. This is critical for functions such as nutrient uptake, waste removal, and maintaining electrical gradients across the cell membrane.
An example of active transport is the sodium-potassium pump (Na⁺/K⁺ ATPase), which moves sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients. Without this continuous action, the concentrations of sodium and potassium inside and outside the cell would become imbalanced, disrupting vital cellular processes such as nerve impulse transmission, muscle contraction, and overall cell homeostasis.
Thus, active transport functions continuously to counteract the effects of diffusion and to ensure that cells maintain the proper conditions for metabolic activities and to prevent harmful imbalances in the concentrations of key molecules.