Questions: A primary active transport process is one in which - an intracellular vesicle fuses with the plasma membrane and releases its contents to the extracellular fluid - molecules pass directly through the phospholipid bilayer of the plasma membrane - molecules move through transport proteins that have been activated by ATP - molecules move across the plasma membrane without an input of energy - the plasma membrane folds inward to form a vesicle containing extracellular material

The answer is the third one: molecules move through transport proteins that have been activated by ATP.

Explanation for each option:

• An intracellular vesicle fuses with the plasma membrane and releases its contents to the extracellular fluid: This describes exocytosis, a form of vesicular transport, not primary active transport.

• Molecules pass directly through the phospholipid bilayer of the plasma membrane: This describes simple diffusion, which is a passive transport process, not requiring energy.

• Molecules move through transport proteins that have been activated by ATP: This is the correct description of primary active transport. In this process, molecules are moved against their concentration gradient through transport proteins that use energy from ATP.

• Molecules move across the plasma membrane without an input of energy: This describes passive transport, such as diffusion or facilitated diffusion, which does not require energy.

• The plasma membrane folds inward to form a vesicle containing extracellular material: This describes endocytosis, another form of vesicular transport, not primary active transport.

In summary, primary active transport involves the movement of molecules through transport proteins that are activated by ATP, allowing the molecules to move against their concentration gradient.