Key concepts in biology study guide

Enzyme activity is significantly influenced by various environmental factors, including temperature, substrate concentration, and pH. Each enzyme has an optimum temperature and an optimum pH at which its activity is maximal. Deviations from these optimal conditions can reduce the rate of reaction. For temperature, increasing it generally increases the kinetic energy of enzyme and substrate molecules, leading to more frequent collisions and a faster reaction rate, up to the optimum. Beyond this, high temperatures cause the enzyme's active site to change shape irreversibly, a process known as denaturation, which dramatically reduces or eliminates its function. Similarly, each enzyme functions best within a narrow pH range. Extreme pH values alter the enzyme's three-dimensional structure, including its active site, leading to denaturation. Substrate concentration also affects reaction rate. Initially, increasing substrate concentration increases the reaction rate as more active sites are occupied. However, once all active sites are saturated with substrate, further increases in substrate concentration will not increase the reaction rate, as the enzyme is working at its maximum capacity.

Osmosis is the net movement of water molecules through a partially permeable membrane from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution). When studying osmosis in living tissues, such as potato cylinders, we often measure changes in mass. If the tissue gains mass, it has absorbed water via osmosis. If it loses mass, it has lost water. To quantify these changes, we calculate the percentage change in mass. This involves finding the difference between the final and initial masses, dividing by the initial mass, and then multiplying by 100. This percentage allows for a standardised comparison between experiments, regardless of the initial mass of the sample.