Question

cells need to bring in molecules to carry out cellular processes. often, this requires moving the molecules across the cell membrane against the concentration gradient. how do these molecules get into the cell?
a. passive transport by diffusion
b. active transport using atp
c. passive transport by osmosis
d. phagocytosis

1. which type of transport does a represent? how do you know?
2. which type of transport does b represent? how do you know?
3. which type of transport does c represent? how do you know?

Explanation:

1. For A:

• Passive transport by diffusion. Molecules move from high to low concentration without energy (ATP) and without a protein channel (as seen in the diagram for A).

1. For B:

• Facilitated diffusion (a type of passive transport). Molecules move from high to low concentration through a protein channel (as in the diagram for B) and no ATP is used.

1. For C:

• Active transport using ATP. Molecules move from low to high concentration (against the concentration gradient) and ATP is involved (as in the diagram for C).

Answer:

1. A represents passive transport by diffusion. Molecules move down the concentration gradient without energy or protein channels.
2. B represents facilitated diffusion (passive transport). Molecules move down the concentration gradient through a protein channel.
3. C represents active transport using ATP. Molecules move against the concentration gradient with ATP use.