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Biology · 3. Enzymes and metabolism

Enzymes, temperature and reaction rate

Design a fair test for the effect of temperature or substrate concentration.

40 minutesContent version: 2.1
Start the interactive pathwayOpen the virtual experiment

Driving question

Why does warming accelerate an enzyme reaction only up to a limit?

Curriculum coverage

Vietnam 2018 and Cambridge: enzymes, reaction rate and environmental effects.

Model scope and limitations

The model shows idealised trends; optimum temperature depends on the enzyme, pH and organism.

Learning objectives

  • Explain temperature effects through collision and denaturation.
  • Identify independent, dependent and control variables.
  • Calculate rate from product or substrate change over time.

Prerequisite knowledge

  • Proteins and three-dimensional structure
  • Concept of rate

Core knowledge

Below the optimum

Increasing temperature generally raises kinetic energy and successful collision frequency.

Above the optimum

Bonds maintaining structure are disrupted; the active site changes shape and rate falls.

Fair test

When testing temperature, keep enzyme, substrate, pH, volumes and timing consistent.

Worked example

If 18 cm³ of product forms in 3 minutes, the mean rate is 6 cm³/min; comparisons require the same interval and conditions.

Misconceptions to avoid

  • Enzymes lower activation energy but do not change ΔG or the equilibrium position.
  • Denaturation is not simply an enzyme “dying”; structure and activity change, sometimes irreversibly.

Virtual experiment procedure: Enzyme kinetics

  1. Choose one independent variable: temperature or substrate concentration.
  2. Use at least five levels and repeat each where possible.
  3. Record product over time, calculate initial rate and plot a graph.

Safety and cautions

  • In a real lab, use a water bath and suitable protection.
  • Do not generalise one enzyme’s optimum to all enzymes.

Evidence to collect

  • A condition–rate table with units and stated control variables.
  • A graph showing rising, optimum and falling regions with a molecular explanation.
Open the virtual experiment

Diagnostic check

1. Which reaction property is mainly changed by an enzyme?

  1. Activation energy
  2. Total product energy
  3. Final equilibrium position
Show answer and explanation

Correct answer: Activation energy

An enzyme provides a pathway with lower activation energy.

2. When testing temperature, which quantity should be controlled?

  1. pH
  2. Temperature
  3. Measured rate
Show answer and explanation

Correct answer: pH

Temperature is independent; pH is an important control variable.

3. How can rate be calculated?

  1. Change in amount / time
  2. Time / change in amount
  3. Amount × time
Show answer and explanation

Correct answer: Change in amount / time

Average rate is the change in quantity divided by elapsed time.

Application practice

1. 24 cm³ of gas is produced in 60 s. What is the mean rate?

  1. 0.40 cm³/s
  2. 2.5 cm³/s
  3. 1440 cm³/s
Show answer and explanation

Correct answer: 0.40 cm³/s

24/60 = 0.40 cm³/s.

2. Why does rate fall sharply above the optimum temperature?

  1. The active site changes through denaturation
  2. All molecules stop moving
  3. Substrate becomes enzyme
Show answer and explanation

Correct answer: The active site changes through denaturation

Heat disrupts interactions maintaining protein structure.

3. What should a strong graph conclusion include?

  1. Trend, numerical evidence and limitation
  2. Only “the graph rises”
  3. A copy of the aim
Show answer and explanation

Correct answer: Trend, numerical evidence and limitation

A scientific conclusion links a claim to measured evidence.

Academic references

  1. OpenStax Biology 2e — peer-reviewed foundational biology

This lesson is maintained against the cited sources below. Simulations are learning models and do not replace supervised physical-laboratory safety procedures.

Content publisher
WebLab STEM
Technical maintainer
Đức Tiến — Control & Automation Engineer