Practical skills Study Guide

Enzymes are biological catalysts that speed up the rate of biochemical reactions without being used up themselves. Their activity is sensitive to changes in certain environmental factors, such as temperature, pH, and substrate concentration. Understanding how these factors influence enzyme reaction rates is crucial in biology. When designing an investigation, we aim to measure the rate of a reaction, which often involves monitoring the disappearance of a substrate or the appearance of a product over time. For instance, in an experiment with catalase enzyme, which breaks down hydrogen peroxide into water and oxygen, we could measure the volume of oxygen gas produced over a set time period or the time taken to produce a certain volume of oxygen. This allows us to calculate a reaction rate. Another example is amylase, which breaks down starch. The disappearance of starch can be monitored using iodine solution, which changes colour in the presence of starch. The independent variable is the factor we purposefully change (e.g., temperature), the dependent variable is what we measure (e.g., reaction rate), and control variables are factors we keep constant to ensure a fair test (e.g., enzyme concentration, substrate volume, pH). Safe experimental practice involves wearing safety goggles, handling chemicals carefully, and being aware of any heated apparatus. Reproducible methods are vital for valid scientific conclusions, requiring clear steps and appropriate equipment use.

Food contains various biological molecules essential for life, such as carbohydrates (sugars and starch), proteins, and lipids (fats and oils). To determine which of these molecules are present in a food sample, we can use specific chemical tests, often called qualitative reagents. Each reagent reacts with a particular biological molecule in a characteristic way, usually by changing colour. For example, Benedict's reagent is used to detect reducing sugars. When heated with a sample containing reducing sugars, it changes from blue to green, yellow, orange, or brick-red, depending on the concentration. Iodine solution tests for starch, turning from yellow/brown to blue/black in its presence. Biuret reagent, composed of potassium hydroxide and copper sulfate solutions, is used for proteins; it changes from blue to lilac/purple if protein is present. Finally, ethanol emulsion test detects lipids. A positive result is indicated by the formation of a cloudy white emulsion. Many of these tests require heating using sensible safety precautions, such as a water bath, to speed up the reaction or to allow the reaction to occur. This practical involves careful measurement, safe handling of chemicals, and accurate observation of colour changes to identify the components of food samples.