Diffusion Osmosis Diffusion is the movement of molecules

Diffusion & Osmosis � � � Diffusion is the movement of molecules - from an area of high concentration - to an area of low concentration This continues until the concentration is equal The difference between 2 areas is called the concentration gradient Movement is always from high to low concentration

Diffusion (Single celled organisms) � � � Single celled organisms use up oxygen & food & produce CO 2 & waste There is generally a gradient between the inside & outside of the cell The cell membrane allows oxygen, CO 2 food across freely (freely permeable) Oxygen/food will diffuse into the cell CO 2/waste will diffuse out of the cell

Food diffusion -single celled organisms � � � Single celled animals (e. g. Amoeba) engulfs food by phagocytosis Food becomes engulfed in a food vacuole Food is digested by enzymes (inside lysosomes) Inside the vacuole there is a high conc. of food products, a low conc. in the cytoplasm The food diffuses from high conc. to low conc.

Multicellular organisms � � � � � In animals Diffusion is important for exchange of gases Blood returning to lungs - high conc. of CO 2, low conc. of oxygen CO 2 diffuses out of blood into air sacs Oxygen diffuses from air sacs into blood Diffusion also important for dissolved food & wastes In plants - CO 2 diffuses from the air into the leaves - water diffuses from the soil into the roots

Role of Cell Membrane � � Cell membrane is semi-permeable Allows small molecules (e. g. water, oxygen) to pass across freely Won’t allow large molecules (e. g. starch) to pass across Membranes have tiny pores or gaps

Water Concentrations � � A solution with the higher water conc (HWC) is said to be HYPOTONIC The solution with the lower water conc (LWC) is HYPERTONIC If the 2 solutions are of equal conc, they are ISOTONIC Molarity (M) is the conc of solute (e. g. sugar/salt) dissolved in water

Effect of osmosis on cells � � � � If a solution outside a cell is hypotonic, water will diffuse in The cell will expand Animal cells will eventually burst Plant cells will swell and become hard - TURGID If a solution outside the cell is hypertonic, water will diffuse out The cell will shrink & shrivel up Plant cells are said to be PLASMOLYSED

Osmosis & Cells � � � � In plants, useful for: - Soil to roots (water into plant) - Xylem to stem (for stem support) - xylem to green leaves (for photsynthesis) In single celled organisms: e. g Paramecium contractile vacuoles control water levels (OSMOREGULATION)