Simple diffusion requires __________.

• A. vesicle formation
• B. a concentration gradient
• C. energy from ATP
• D. carrier proteins

Answer: (B)

Verified step by step guidance

1. Understand the concept of simple diffusion: Simple diffusion is a passive transport process where molecules move from an area of higher concentration to an area of lower concentration without the need for energy or assistance from proteins.
2. Identify the key requirement for simple diffusion: A concentration gradient is necessary for simple diffusion to occur. This gradient provides the driving force for molecules to move across the membrane.
3. Eliminate incorrect options: Vesicle formation is associated with processes like endocytosis, not simple diffusion. Energy from ATP is required for active transport, not passive processes like diffusion. Carrier proteins are involved in facilitated diffusion, not simple diffusion.
4. Focus on the correct answer: The correct requirement for simple diffusion is a concentration gradient, as it allows molecules to move passively across the membrane.
5. Summarize the reasoning: Simple diffusion relies solely on the natural movement of molecules down their concentration gradient, without the involvement of energy, vesicles, or carrier proteins.