Cell Membrane Transport

Very small, nonpolar molecules like oxygen (O₂) and carbon dioxide (CO₂) cross freely across the phospholipid bilayer. This is an example of -

• Simple diffusion

• Facilitated diffusion

• Osmosis

• Protein pumps

Most water molecules cross the cell membrane using specific channel proteins called aquaporins. They are always open for water molecules to pass through and don't require energy. This is an example of -

• Simple diffusion

• Facilitated diffusion

• Protein pumps

• Endocytosis

The diffusion of water molecules across a cell membrane.

Water molecules move from the side with the highest water concentration to the side with the lowest water concentration until equilibrium is reached. This is an example of -

• Endocytosis

• Exocytosis

• Cellular respiration

• Osmosis

Glucose molecules cross the cell membrane through carrier proteins embedded in the membrane. The proteins change shape when glucose binds to them, which allows the glucose to enter the cell. No energy is needed for the protein to change shape. This is an example of -

• Simple diffusion

• Facilitated diffusion

• Osmosis

• Protein pumps

Sodium ions are moved across the cell membrane through special carrier proteins. These proteins require ATP energy to change shape, but this energy allows the sodium ions to be pushed against the concentration gradient. This is an example of -

• Exocytosis

• Facilitated diffusion

• Simple diffusion

• Protein pumps

A cell engulfs food by infolding its cell membrane and forming a vesicle to bring the nutrient-rich food into the cytoplasm. This is an example of -

• Facilitated diffusion

• Protein pumps

• Endocytosis

• Exocytosis

A cell can release certain substances by packaging them in vesicles. The vesicles migrate to the cell membrane and merge with it. This creates an opening for the substances to be released. This is an example of -

• Exocytosis

• Endocytosis

• Facilitated diffusion

• Protein pumps

Doesn't require energy (ATP)

Substances move from [high] to [low]

Very tiny, nonpolar molecules can freely move across cell membrane

• Simple diffusion

• Facilitated diffusion

• Endocytosis

• Protein pumps

Doesn't require energy (ATP)

Substances move from [high] to [low]

Molecules cross the cell membrane through channel proteins

These channel proteins are like pores or tunnels that remain open 24/7

• Simple diffusion

• Facilitated diffusion

• Endocytosis

• Protein pumps

Requires energy (ATP) for substances to move across cell membrane

Substances move from [low] to [high]

Molecules cross the cell membrane through special channel proteins that change shape with the help of energy (ATP).

• Simple diffusion

• Facilitated diffusion

• Endocytosis

• Protein pumps