Key concepts in biology Study Guide

Enzymes are biological catalysts, speeding up biochemical reactions without being used up. Their activity is sensitive to environmental conditions. Temperature affects enzymes by increasing kinetic energy; initially, this speeds up reactions, but excessively high temperatures cause denaturation, permanently altering the active site and rendering the enzyme inactive. Substrate concentration influences reaction rate because more substrate molecules mean more frequent collisions with enzyme active sites, leading to increased product formation up to a saturation point. pH also plays a crucial role; each enzyme has an optimum pH at which its active site structure is maintained, allowing maximum activity. Deviations from this optimum pH can alter the enzyme's three-dimensional shape, causing denaturation and reducing efficiency.

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.