concentration gradient? None of these is correct Active transport Simple diffusion Phagocytosis Facilitated diffusion 1 pts
Question 42 What type of movement is passive and down a concentration gradient? None of these is correct Active transport Simple diffusion Phagocytosis Facilitated diffusion 1 pts
The Correct Answer and Explanation is:
Correct Answer:
Simple diffusion
Explanation
Movement across a cell membrane can happen in different ways depending on whether the process uses energy and the direction of the concentration gradient. A concentration gradient exists when there is a difference in the concentration of a substance across a space, such as across a membrane. Movement down a concentration gradient means particles are moving from an area of higher concentration to an area of lower concentration.
The correct answer to the question asking for a type of movement that is passive and moves down the concentration gradient is simple diffusion.
Simple diffusion is the movement of molecules without the use of energy or assistance from proteins. It happens naturally as molecules spread out evenly in a space. This process is passive because it does not require the cell to expend any energy, such as ATP. It is driven purely by the kinetic energy of the molecules themselves.
Examples of simple diffusion include oxygen and carbon dioxide passing through the cell membrane. These molecules are small and non-polar, so they can easily move through the lipid bilayer of the cell membrane.
Other options listed in the question are incorrect in this context:
- Active transport requires energy and moves substances against their concentration gradient.
- Phagocytosis is a form of endocytosis in which the cell engulfs large particles, which also requires energy.
- Facilitated diffusion is passive but involves protein channels or carriers to help move molecules across the membrane. While it is also down the gradient, it is not “simple” diffusion because it requires a protein.
- None of these is correct is not valid since one option (simple diffusion) fits perfectly.
Therefore, simple diffusion is the best answer for a passive process that moves substances down their concentration gradient.
