Bio Common Defns

Complied by Mrs Eunice Chan/Oct2012, revised Aug2020 ©The Biology Jotter Book Glossary of key terms for O Level Biology Word Definition Diffusion Net movement of molecules from a region of their higher concentration to a region of their lower concentration, down a concentration gradient Osmosis Movement of water molecules from a region of higher water potential to a region of lower water potential, across a partially permeable membrane Water potential A measure of the tendency of water to move from one place to another Concentration gradient Difference in concentration between two regions Plasmolysis Shrinking of cytoplasm away from the cell wall when the plant cells are immersed in a solution more concentrated than their cell sap Turgor pressure Pressure exerted outwards on the plant cell wall due to the water in the cell, giving the cell its turgidity. Active transport Process in which energy from respiration is used to move molecules against a concentration gradient, from a region of lower concentration to a region of higher concentration Condensation reaction A chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one molecule of water Hydrolysis A chemical reaction in which water molecule is needed to break up a complex molecule into smaller molecules Reducing sugars Sugars which can reduce the copper (II) to copper (I) E.g. glucose, maltose, fructose, lactose Saturated fats Fats with straight fatty acid chains and are found mostly in animals Unsaturated fats Fats with bent fatty acid chains and are found mostly in vegetables Emulsion A suspension of small drops of a liquid in another liquid Kwashiorkor Protein-deficiency disease in which children have swollen stomachs and dry, scaly skin Enzymes Biological catalysts made with proteins which alter the rate of chemical reactions without themselves being chemically changed at the end of the reactions Activation energy Energy needed to start a chemical reaction Active site Depression on the surface of an enzyme molecule into which the substrate molecule can fit

Complied by Mrs Eunice Chan/Oct2012, revised Aug2020 ©The Biology Jotter Book Word Definition Optimum temperature Temperature at which enzyme is most active, catalysing the largest number of reactions per second Optimum pH pH value at which enzyme is most active, catalysing the largest number of reactions per second Denaturation Change in the three-dimensional structure of an enzyme or any other soluble protein, caused by heat or extreme pH changes Limiting factor Any factor that directly affects a process if its quantity is changed Peristalsis Rhythmic wave-like contractions of the wall of the gut caused by alternate contractions of the circular and longitudinal muscles in the walls to help push food along the gut Emulsification of fats Occurs when bile break big blobs of fat into smaller fat droplets Egestion Removal of undigested food from th