Osmosis

Osmosis

Movement of water across a selectively permeable membrane from low solute concentration to high solute concentration

Diffusion

Passive movement of molecules from an area of high concentration to low concentration due to random molecular motion

Passive transport

Movement of molecules across the cell membrane without energy input, following the concentration gradient

Active transport

Movement of molecules across the cell membrane using ATP, often against the concentration gradient

Isotonic solution

A solution with the same solute concentration as the cell; no net water movement occurs

Hypertonic solution

A solution with higher solute concentration than the cell; water moves out and the cell shrinks

Hypotonic solution

A solution with lower solute concentration than the cell; water moves in and the cell swells

Endocytosis

Process where the cell membrane engulfs material to bring it inside the cell

Exocytosis

Process where vesicles fuse with the cell membrane to release substances outside the cell

Phagocytosis

A type of endocytosis where the cell engulfs large particles or microorganisms (“cell eating”)

Phospholipids and cholesterol

Help compartmentalize water and maintain membrane structure

Protein channels

Allow specific molecules to cross the membrane selectively

Intramembrane proteins

Can function as enzymes and recognition molecules

Transmembrane proteins

Act as receptors, passing signals into the interior of the cell

Importance of diffusion

Disperses molecules, balancing concentrations and supporting essential cellular functions

Kinetic energy of molecules

Determined by temperature; in mammals it’s ~38°C, with energy linked to mass and velocity

Movement of molecules in diffusion

Molecules collide and ricochet randomly, changing direction constantly, leading to even distribution over time