Key concepts in biology Study Guide

Enzymes are biological catalysts, typically proteins, that speed up specific biochemical reactions. Their catalytic activity relies on their unique three-dimensional structure, particularly the active site. The active site is a specific region on the enzyme that binds to a substrate molecule. This binding is highly specific, often likened to a 'lock and key' mechanism, dependent on the complementary shapes of the active site and the substrate. If the environmental conditions, such as temperature or pH, deviate significantly from the enzyme's optimal range, the enzyme's structure can be altered. Extreme heat can cause the protein's bonds to break or rearrange, changing its shape. Similarly, large changes in pH can affect the charges on amino acid residues, altering the enzyme's folding. This change in the enzyme's overall three-dimensional shape, specifically affecting the active site, is called denaturation. When the active site changes shape, the substrate can no longer bind effectively, or the enzyme's catalytic efficiency is severely reduced or lost entirely, rendering the enzyme inactive. Denaturation is often irreversible.

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.