AP BIOLOGY

Detailed explanation-1: -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-2: -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.

Detailed explanation-3: -Active transport moves molecules and ions from lower concentration to higher concentration with the help of energy in the form of ATP. On the other hand, passive transport moves molecules and ions from a higher concentration to lower concentration without any energy.

Detailed explanation-4: -Primary active transport moves ions across a membrane and creates a difference in charge across that membrane. The primary active transport system uses ATP to move a substance, such as an ion, into the cell, and often at the same time, a second substance is moved out of the cell.