MYP Biology sample question: Enzymes and temperature

A student measures how quickly the enzyme amylase breaks down starch at different temperatures. The rate is slow at 10 °C, fastest at 37 °C, and zero at 70 °C.

1. (a)Explain why the rate is slow at 10 °C.[2]
   Show the mark scheme for (a)

   • • Particles have less kinetic energy and move more slowly (1)
   • • so there are fewer collisions between enzyme and substrate (1)
2. (b)Explain why there is no reaction at 70 °C.[3]
   Show the mark scheme for (b)

   • • The enzyme has been denatured (1)
   • • The shape of the active site has changed (1)
   • • so the substrate can no longer fit into it (1)
3. (c)State what is meant by the optimum temperature of an enzyme.[1]
   Show the mark scheme for (c)

   • • The temperature at which the enzyme works fastest (1)

Use the words active site, substrate and denatured. Low temperature slows an enzyme; high temperature destroys it.