Question

endocytosis and exocytosis are forms of active transport. what is active transport? (1 point)
○ the movement of molecules down a concentration gradient from high to low, using energy
○ the movement of molecules up a concentration gradient from low to high, using no energy
○ the movement of molecules down a concentration gradient from high to low, using no energy
○ the movement of molecules up a concentration gradient from low to high, using energy

Explanation:

To determine the correct definition of active transport, we recall the key characteristics: active transport moves molecules against (up) the concentration gradient (from low to high concentration) and requires energy (usually ATP). Let's analyze each option:

• First option: Movement down (high to low) gradient with energy is incorrect; down - gradient with no energy is passive (like diffusion).
• Second option: Movement up gradient with no energy is wrong, as active transport needs energy.
• Third option: Movement down gradient with no energy is passive transport (e.g., diffusion, osmosis).
• Fourth option: Movement up (low to high) concentration gradient and using energy matches the definition of active transport.

Answer:

the movement of molecules up a concentration gradient from low to high, using energy