Which of the following statements about passive transport is FALSE?
Substances move down their electrical or chemical gradient.
An example is diffusion through cell membranes.
It requires protein channels or gates in the cell membrane.
It does not require energy input.
Substances move down their concentration gradient.
An example is facilitated diffusion through membrane proteins.
The correct answer and explanation is :
The correct answer is: “It requires protein channels or gates in the cell membrane.”
Explanation:
Passive transport is a biological process where substances move across a cell membrane without the need for energy input (ATP). This process occurs in the direction of the concentration gradient, meaning from an area of high concentration to an area of low concentration. Here’s a breakdown of each statement:
- “Substances move down their electrical or chemical gradient”: This is true. Passive transport depends on the movement of substances down their concentration gradient (or electrochemical gradient, if ions are involved), meaning molecules naturally move from areas of higher concentration to areas of lower concentration.
- “An example is diffusion through cell membranes”: This is true. Simple diffusion is one of the forms of passive transport where molecules move directly through the lipid bilayer of the membrane, typically small, nonpolar molecules like oxygen or carbon dioxide.
- “It requires protein channels or gates in the cell membrane”: This is false. Not all forms of passive transport require protein channels or gates. Simple diffusion, for example, does not need any protein channels; small, nonpolar molecules can pass directly through the phospholipid bilayer of the membrane. However, facilitated diffusion, a specific type of passive transport, does require proteins such as channels or carriers to assist in the movement of larger or polar molecules like glucose or ions.
- “It does not require energy input”: This is true. Passive transport does not require ATP or other energy sources because it occurs spontaneously due to the concentration gradient, which is a natural tendency for particles to move from high to low concentration.
- “Substances move down their concentration gradient”: This is true. Passive transport always involves the movement of substances down their concentration gradient, meaning from high to low concentration.
- “An example is facilitated diffusion through membrane proteins”: This is true. Facilitated diffusion is a type of passive transport where molecules that cannot pass directly through the lipid bilayer use membrane proteins (either channels or carriers) to move across the membrane.
In summary, passive transport involves movement of substances down their concentration gradient and does not require energy input. While facilitated diffusion does require protein channels, simple diffusion does not, making the statement about requiring protein channels or gates the only false one.