AP BIOLOGY

Detailed explanation-1: -Active transport: moving against a gradient To move substances against a concentration or electrochemical gradient, a cell must use energy. Active transport mechanisms do just this, expending energy (often in the form of ATP) to maintain the right concentrations of ions and molecules in living cells.

Detailed explanation-2: -Some molecules even need an input of energy to help get them across the cell membrane. The movement of molecules across a membrane without the input of energy is known as passive transport. When energy (ATP) is needed, the movement is known as active transport.

Detailed explanation-3: -There are two basic ways that substances can cross the plasma membrane: passive transport, which requires no energy; and active transport, which requires energy.

Detailed explanation-4: -Diffusion is the movement of particles from high concentration to low concentration in a substance. This process is essential for life on Earth, allowing for the movement of molecular compounds into and out of the cell.