What is active transport?

What is active transport?

• A. The movement of molecules into lower concentration without energy
• B. The movement of molecules into higher concentration that does require energy
• C. The diffusion of water through a membrane
• D. The formation of waste products

Answer: (B)

Active transport moves substances across a cell membrane from where they are less concentrated to where they are more concentrated, which is against their natural gradient, and it requires energy. The energy often comes from ATP and is used to power transport proteins like pumps that carry specific molecules (for example, the sodium–potassium pump) or to drive processes such as endocytosis. This is different from passive transport, where substances diffuse down their gradient without energy input. So the description that says movement into a higher concentration that requires energy best captures active transport. The other ideas describe diffusion or unrelated processes, which don’t fit active transport.

Active transport moves substances across a cell membrane from where they are less concentrated to where they are more concentrated, which is against their natural gradient, and it requires energy. The energy often comes from ATP and is used to power transport proteins like pumps that carry specific molecules (for example, the sodium–potassium pump) or to drive processes such as endocytosis. This is different from passive transport, where substances diffuse down their gradient without energy input. So the description that says movement into a higher concentration that requires energy best captures active transport. The other ideas describe diffusion or unrelated processes, which don’t fit active transport.