AP BIOLOGY

Detailed explanation-1: -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: -Gases like carbon dioxide and oxygen can move across the cell membrane via diffusion. Diffusion is the movement of gas molecules from a region of higher concentration, to a region of lower concentration through a semi-permeable membrane.

Detailed explanation-3: -Basic types of membrane transport, simple passive diffusion, facilitated diffusion (by channels and carriers), and active transport [8]. Even simple passive diffusion requires energy to cross a bilayer membrane.

Detailed explanation-4: -Osmosis. Osmosis is the diffusion of water through a semipermeable membrane according to the concentration gradient of water across the membrane.

Detailed explanation-5: -An example of passive transport across a cell membrane is the diffusion of oxygen from the alveoli into the blood. Passive transport is a type of transport that does not use energy. There are three main types of passive transport, diffusion, facilitated diffusion and osmosis.