Cell Transport System

Passive transport

Substances move from high concentration to low concentration (like rolling downhill). The cell does NOT use energy.

Diffusion

Movement of small molecules (like oxygen, carbon dioxide) from an area of high concentration to low concentration

Facilitated Diffusion

• Large or charged molecules (like glucose or ions) can’t pass directly through the membrane

• They pass through protein channels or carrier proteins

• Still moves from high to low concentration

• No energy is needed

Osmosis

• Special type of diffusion: movement of water molecules through a semi-permeable membrane

• Moves from high water concentration to low water concentration

• Water tries to balance solute concentrations on both sides

Hypotonic

A type of osmosis where water enters cell making the cell swell or burst

Hypertonic

A type of osmosis where water leaves cell making the cell shrink

Active transport

The cell uses energy (ATP) to move substances against the concentration gradient (from low to high concentration).

Protein Pumps

• Transport proteins use energy to push molecules against the gradient

• Example: Sodium-potassium pump (important in nerve cells)

Endocytosis

• The cell engulfs materials by folding its membrane around it

• Creates a vesicle to bring substances inside

• Used for large molecules like nutrients or bacteria

Phagocytosis

“cell eating” (solids like bacteria)

Pinocytosis

“cell drinking” (liquids)

Exocytosis

• Vesicles inside the cell fuse with the membrane and release substances outside

• Used to get rid of waste, or release hormones/enzymes