The cell does not need to expend energy (ATP) in order to perform facilitated diffusion (C) pinocytosis (B) osmosis (A) Both A and C are correct active transport (D)
The Correct Answer and Explanation is:
Correct Answer: (E) Both A and C are correct
Explanation:
Cells transport substances across their membranes using various mechanisms, which are broadly classified into passive transport and active transport. Passive transport does not require the use of cellular energy (ATP), while active transport does.
Osmosis (A) is a classic example of passive transport. It refers to the movement of water molecules from an area of lower solute concentration to an area of higher solute concentration across a selectively permeable membrane. This movement occurs due to the natural kinetic energy of water molecules and does not require ATP. Osmosis is essential in maintaining the cell’s internal environment and is vital in processes such as water absorption by plant roots and water reabsorption in the kidneys.
Facilitated diffusion (C) is another form of passive transport, used for molecules that cannot directly diffuse across the cell membrane due to their size, polarity, or charge. Instead, they move through protein channels or carrier proteins embedded in the membrane. Like osmosis, facilitated diffusion moves substances down their concentration gradient—from high to low concentration—and does not require cellular energy (ATP). Examples include the movement of glucose and amino acids into cells via carrier proteins.
On the other hand, pinocytosis (B) and active transport (D) do require ATP. Pinocytosis, often called “cell drinking,” is a form of endocytosis in which the cell engulfs extracellular fluid and its dissolved substances into vesicles. This process is energy-dependent. Similarly, active transport involves the movement of substances against their concentration gradient, which demands energy input from ATP. A well-known example is the sodium-potassium pump, which maintains ion gradients essential for nerve impulse transmission.
Therefore, since both osmosis and facilitated diffusion are passive processes that do not require energy, the correct answer is:
(E) Both A and C are correct.
