Key concepts in biology Study Guide

Enzymes are biological catalysts that speed up biochemical reactions. They have an 'active site' which is specific to the 'substrate' they act upon, much like a lock and key. The activity of an enzyme is significantly affected by environmental factors, particularly temperature and pH. Each enzyme has an 'optimum pH' at which its activity is maximal. Deviations from this optimum pH, either too acidic or too alkaline, can cause the enzyme's active site to change shape, a process known as denaturation. When denatured, the enzyme can no longer bind effectively with its substrate, leading to a decrease in its activity or even complete loss of function. This practical investigates how varying pH levels influence the rate of an enzyme-catalysed reaction, typically using amylase and starch, or catalase and hydrogen peroxide. By accurately controlling the pH and measuring the reaction rate, we can determine the enzyme's optimum pH and understand the impact of pH changes on enzyme structure and function. Identifying the optimum pH for an enzyme-controlled reaction provides insight into the conditions under which that enzyme is most effective, reflecting its physiological role within an organism.

To compare how much water plant or animal tissue has absorbed or lost during osmosis, we use the percentage change in mass. The calculation uses the formula: ((final mass - initial mass) / initial mass) × 100. A positive result means the tissue gained water (mass increase), while a negative value means it lost water (mass decrease). This method allows for fair comparison between samples, regardless of their starting size, making experimental results more meaningful when analysing the effects of osmosis.