Which of the following factors affects enzyme activity?

Step 1: Analyze the question The question asks which factor affects enzyme activity. Enzymes are biological catalysts (proteins) that speed up chemical reactions in living things.

Step 2: Explain the concept Enzyme activity depends on the enzyme's three-dimensional shape, especially its active site. The main factors that affect it are:

• Temperature
• pH
• Substrate concentration
• Enzyme concentration
• Inhibitors and activators

How temperature works:

• At low temperatures, enzymes are inactive or work very slowly because molecules have little kinetic energy.
• As temperature rises, the rate increases until it reaches the optimum temperature. For human enzymes this is about 37 °C.
• Above the optimum, the enzyme is denatured. Its shape, including the active site, is destroyed and it can no longer work.

Step 3: Check each option

• A. Atmospheric pressure: This has no direct effect on enzymes in cells. ✗
• B. Oxygen: It is a reactant in respiration, but it is not a standard factor affecting enzyme activity. ✗
• C. Carbon dioxide: It is not a standard factor either. ✗
• D. Temperature: It directly changes the rate of enzyme action and can denature enzymes. ✓
• E. Rainfall: This is a weather condition with no direct effect on enzymes. ✗

Step 4: Answer The correct option is D. Temperature.

Exam tip: Remember the enzyme factors with "T-pH-SEI": Temperature, pH, Substrate concentration, Enzyme concentration, Inhibitors. If you see temperature or pH among the options in an enzyme question, it is almost always the answer.