Edexcel A Level (IAL) Biology -5.21 The Effect of Temperature on Enzyme Reactions- Study Notes- New Syllabus

Effect of Temperature on Enzyme Activity (with Q₁₀)

🌱 Introduction

Enzymes control almost every reaction in living organisms. Temperature directly affects how fast enzymes work, which then impacts growth, metabolism, reproduction and survival in plants, animals and microorganisms.

🌡️ How Temperature Affects Enzyme Activity

Key Points

• Enzymes work best at an optimum temperature.
• Below optimum: reactions are slow.
• At optimum: reactions are fastest.
• Above optimum: enzymes denature because their active site loses shape.

Why this happens?

• Heat gives molecules more kinetic energy, increasing enzyme-substrate collisions.
• Too much heat breaks bonds in the enzyme structure, causing denaturation.

🔢 Q₁₀ Value (Temperature Coefficient)

What is Q₁₀?

Q10 tells how much the rate of a biological reaction increases when temperature rises by 10°C.

Formula:

Q₁₀ = Rate at higher temp / Rate at lower temp

Most biological reactions have a Q₁₀ of around 2 – meaning the reaction rate roughly doubles for every 10°C increase.

🌿 Impact on Plants

• Higher temperature increases photosynthesis and respiration up to optimum.
• Above optimum, enzymes of photosynthesis and germination denature, slowing growth.
• Flowering, seed formation and nutrient uptake drop at high temperatures.
• In cold conditions, seed germination and enzyme-controlled growth slow down.

Example
Starch-converting enzymes in seeds slow down in cold soil, delaying germination.

🐾 Impact on Animals

• Metabolic rate rises with temperature because enzyme activity increases.
• In warm environments, ectotherms (fish, reptiles) show faster movement and feeding.
• Extremely high temperatures denature enzymes, reducing survival.
• Temperature influences digestion rate, muscle activity and reproduction.

Example

Fish in warmer water have higher Q10-driven metabolic rates.

🦠 Impact on Microorganisms

• Bacteria and fungi grow fastest near their enzyme optimum temperature.
• High temperatures denature enzymes and kill cells.
• Low temperatures slow down enzyme-driven processes like respiration and division.
• Pathogens multiply faster in warm conditions because their enzymes work quicker.

Example
Bread molds grow rapidly in warm, moist environments but slowly in the fridge.

📊 Summary Table