lesson
An active site supports a particular reaction
1 · Learn
Enzymes are biological catalysts. Their active sites interact with particular substrates, helping reactions occur faster without the enzyme being used up overall. Temperature and pH can affect activity.
High temperatures or unsuitable pH can alter an enzyme's structure and active site. A lower rate at a low temperature is not automatically evidence that the enzyme has been permanently denatured.
2 · Worked example
Heating above an enzyme's suitable range can change the active site so the substrate no longer interacts effectively. Cooling a working reaction can instead slow collisions without necessarily destroying the enzyme.
3 · Your turn
Why is 'any decrease in rate proves denaturation' an unsafe conclusion?
Check your answer
Other factors, including lower temperature or substrate availability, can reduce rate without permanent structural change.
4 · Apply your learning
Analyse a supplied rate-temperature graph and distinguish the observed pattern from the proposed molecular explanation.
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Use supplied data and approved diagrams. Laboratory work requires qualified supervision, suitable equipment and a risk assessment. No independent chemical, electrical, heating, radiation or biological-culture experiments. Human biology is general education, not personal diagnosis or treatment.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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