AP BIOLOGY

Detailed explanation-1: -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. Active transport moves molecules against their concentration gradient, from an area of low concentration to an area of high concentration.

Detailed explanation-2: -Not everything enters the cell through passive transport. Only the smallest molecules like water, carbon dioxide, and oxygen can freely diffuse across cell membranes. Larger molecules or charged molecules often require an input of energy to be transported into the cell.

Detailed explanation-3: -Facilitated diffusion is the passive transportation of ions or molecules across the cell membrane through specific transmembrane integral proteins. The molecules, which are large and insoluble require a carrier substance for their transportation through the plasma membrane.

Detailed explanation-4: -There are two major ways that molecules can be moved across a membrane, and the distinction has to do with whether or not cell energy is used. Passive mechanisms like diffusion use no energy, while active transport requires energy to get done.