2.51: Understand why simple, Unicellular Organisms can Rely on Diffusion for Movement of Substances In and Out of the Cell

DIFFUSION: Passive net movement of particles down the concentration gradient (from region of high concentration to region of low concentration) until equilibrium

UNICELLULAR ORGANISMS: Organisms composed of a single cell - Bacteria, Fungus, Yeast

DIFFUSION IN UNICELLULAR ORGANISMS

Diagram showing the Relation between Surface area and Volume

EXPLANATION: As Unicellular organisms are composed of a single cell, they have a larger surface area in relation to their volume, and hence have a large surface area to volume ratio With a large surface area to volume ratio, Unicellular organisms therefore have efficient rate of diffusion, allowing cell to rely solely on diffusion to transport necessary substances in and out of the cell

COMMON FEATURES OF EXCHANGE SURFACES: Thin Cell Walls Thin cell walls (one cell thick) to minimise distance of diffusion, increasing the rate of diffusion Large Surface Area to Volume Ratio Unicellular organisms are commonly long, thin, flat or folded to increase surface area to volume ratio, increasing the rate of diffusion Moist Unicellular organisms have moist membranes to allow substances to diffuse easily