Question

which of these is an example of active transport?
multiple choice
the diffusion of oxygen from a place of high concentration to a place of lower concentration
the facilitated diffusion of k+
the transport of glucose down its concentration gradient
the transport of na+ from a place of low concentration to a place of higher concentration
the transport of cl- following its concentration gradient

Explanation:

Active transport moves substances against their concentration gradient, requiring energy. The options with substances moving along their concentration gradients (diffusion, facilitated diffusion) are passive transport. Only the transport of Na⁺ from low to high concentration is against the gradient and is active transport.

Answer:

The transport of Na⁺ from a place of low concentration to a place of higher concentration