GCE O Level Biology: Movement of Substances, Enzymes and Nutrients

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

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