IGCSE BIO 3. movement in and out of cells

diffusion

net movement of particles from a region of their higher concentration to a region of their lower concentration, down a concentration gradient, as a result of their random movement

factors affecting rate of diffusion

temperature, diffusion distance, concentration gradient, surface area

role of water in living organisms

as a solvent (as cytoplasm, for metabolic reactions to happen, for transport, for excretion), makes plant cells turgid and prevent wilting, raw material for photosynthesis

osmosis

net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane

when plant cell is in solution with higher water potential…

it becomes turgid

when plant cell is in solution with lower water potential…

it becomes flaccid → plasmolysed

active transport

movement of particles through a cell membrane from a region of lower concentration to a region of lower concentration, against concentration gradient, using energy from respiration, involving shape changes of carrier proteins on cell membrane