Passive Transport
Passive transport is when molecules move "down" the concentration gradient, or from high to low concentration. This does not require ATP energy from the cell.
Learn about 3 types of Passive Transport below!
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Simple Diffusion
Simple Diffusion
Diffusion is the movement of molecules through the cell membrane from a region of higher concentration to a region of lower concentration. Molecules move "down" the concentration gradient. The molecules pass freely through the lipids in the cell membrane.
Diffusion is passive. This means that diffusion does NOT require ATP energy to happen. Diffusion will continue to occur until molecules are in equilibrium, which means their concentrations are equal on both sides of the membrane.
Examples include carbon dioxide and oxygen diffusing through the cell membrane.
Watch the video on the left from 0:00 to 2:00.
Facilitated Diffusion
Facilitated Diffusion
Facilitated diffusion is when molecules that are unable to slip through the lipid bilayer pass through protein channels, which act like tunnels through the cell membrane.
Like regular diffusion, molecules still move from high concentration to low concentration through the cell membrane until equilibrium is reached.
Facilitated diffusion is passive, which means ATP is NOT necessary for it to happen.
An example is glucose passing into the cell through a protein channel.
Watch the video on the left.
Osmosis
Osmosis
Osmosis is the diffusion of water molecules through a cell membrane. The netmovement of water into a cell will cause it to swell. The net movement of water out of a cell will cause it to shrink.
Just like other molecules that can diffuse through the membrane, water (H2O) moves from a region of higher concentration to a region of lower concentration. Molecules move "down" the concentration gradient. The molecules pass freely through the lipids and pores in the cell membrane.
An example is when you water a wilted plant. The water passes into the plant cells by osmosis, and the plant regains its shape because its cells are now full of water pressure.
Osmosis is passive. This means that diffusion does NOT require ATP energy to happen.
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