The effect of pH on enzymes (core practical): Key concepts in biology: Biology: GCSE (9:1)

Enzyme

Biological catalysts which speed up reactions without being used up

Enzymes and temperature

The enzyme rate increases as temperature increases up to an optimum, after which the enzyme becomes denatured

Enzymes and pH

The reaction rate decreases as the pH moves away from the enzyme's optimum pH

Denature

When the active site changes shape and can no longer bind to a substrate due to unsuitable temperature or pH

Active site

The part of an enzyme where the substrate binds

Substrate

Reactant of an enzyme catalysed reaction

Product

A substance produced in a chemical reaction

Lock and key theory

When a substrate fits into its enzyme just like a key fits a lock

Optimum rate

An ideal pH or temperature value that results in maximum enzyme activity

Amylase

A carbohydrase enzyme that breaks starch down into sugars

Starch

A large carbohydrate found in plants made up of many glucose molecules

Iodine solution

Turns from orange to blue-black in the presence of starch, will remain orange if starch has been broken down by amylase

Buffer solution

A solution that controls and keeps the pH of a solution to a specific range

Water bath

A container of water heated to a given temperature for control purposes

Spotting tile

Equipment used to observe the colour changes of small quantities of reacting mixtures

Time taken for starch to break down

The dependent variable or factor that is measured in this experiment to investigate pH and enzyme activity

pH condition

The independent variable or factor that is changed in this experiment to investigate pH and enzyme activity

Temperature

A variable that should be controlled in this experiment to ensure the results are valid

End of reaction

The reaction can be confirmed as complete when iodine on the spotting tile no longer changes colour from orange to blue-black

Examples of other control variables

To ensure the results are valid the volumes and concentrations of all solutions should be controlled

Expected results

Amylase will break down starch effectively at an optimum pH, this can be identified as the pH condition that causes iodine to remain orange the quickest