Movement into and out of cells
Diffusion and osmosis
Diffusion is the net movement of particles from a higher to a lower concentration, down a concentration gradient, because of random movement. It's faster with a steeper gradient, larger surface area, shorter distance and higher temperature. Osmosis is the net movement of water molecules from a dilute solution (high water potential) to a more concentrated solution (low water potential) through a partially permeable membrane. Plant cells in water become turgid; in strong sugar solution they become flaccid then plasmolysed. Animal cells in water may burst; in strong solutions they shrink.
≈ 40 minActive transport and surface area
Active transport moves particles against a concentration gradient (from low to high concentration) using energy from respiration and carrier proteins in the membrane. Root hair cells use it to absorb mineral ions from dilute soil water; gut cells use it to absorb glucose. Larger organisms have a smaller surface area to volume ratio, so they need specialised exchange surfaces and transport systems.
≈ 30 min