Which statement best explains the difference between active and passive transport?

• A. Active transport only occurs in plant cells, while passive transport only occurs in animal cells.
• B. Active transport requires energy input from the cell, while passive transport does not.
• C. Both active and passive transport require ATP to move molecules across the membrane.
• D. Passive transport moves substances against their concentration gradient, while active transport moves them down their gradient.

Answer: (B)

Verified step by step guidance

1. Step 1: Begin by understanding the key concepts of active and passive transport. Active transport is a process where molecules are moved across a cell membrane against their concentration gradient (from low to high concentration) and requires energy input, typically in the form of ATP. Passive transport, on the other hand, moves molecules down their concentration gradient (from high to low concentration) and does not require energy input.
2. Step 2: Evaluate the first statement: 'Active transport only occurs in plant cells, while passive transport only occurs in animal cells.' This statement is incorrect because both active and passive transport occur in all types of cells, including plant and animal cells.
3. Step 3: Evaluate the second statement: 'Active transport requires energy input from the cell, while passive transport does not.' This statement is correct because active transport relies on ATP or other energy sources, while passive transport occurs naturally without energy expenditure.
4. Step 4: Evaluate the third statement: 'Both active and passive transport require ATP to move molecules across the membrane.' This statement is incorrect because passive transport does not require ATP or any energy input; it relies on the natural movement of molecules down their concentration gradient.
5. Step 5: Evaluate the fourth statement: 'Passive transport moves substances against their concentration gradient, while active transport moves them down their gradient.' This statement is incorrect because it reverses the definitions of active and passive transport. Active transport moves substances against their gradient, while passive transport moves them down their gradient.