Enzymes: how they speed reactions, and what pH and temperature do

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Use this

   Enzyme drawing (model, not to scale).

3. 1.

   Ari studies an enzyme drawing. Letter A points to the notch on top where the small molecule sits. What is A called?

   • The substrate
   • The product
   • A notch that fits any molecule
   • The active site
4. 2.

   Esme looks at the right side of the drawing, after the reaction. Letter D points to the separate beads. What are they called?

   Use the picture in question 1.

   • The substrates
   • The cofactors
   • The enzyme, used up
   • The products
5. 3.

   Jun’s class compares two energy diagrams of one reaction, one with an enzyme and one without. Which curve shows the reaction with the enzyme?

   • Curve 1, because the enzyme gives the reaction extra energy to climb higher
   • Curve 2, because the enzyme is used up on the way up
   • Curve 2, because the enzyme lowers the energy needed to start
   • Curve 1, because the enzyme makes the reaction harder to start
6. 4.

   Kira compares curves A and B for one reaction. Only one curve has an enzyme. Which curve is it, and why?

   • Curve A, because enzymes make a reaction release more energy
   • Curve B, because its lower peak needs less energy to start
   • Curve A, because its higher peak shows the enzyme adding energy
   • Curve B, because the enzyme is gone before the reaction ends
7. 5.

   Luz reads two energy curves for one reaction: X without an enzyme and Y with one. Which statement about them is true?

   • Curve X ends lower, so it releases more energy
   • Curve Y starts higher, so the enzyme brings extra energy
   • Both curves start and end at the same energy; the peaks differ
   • Curve Y stops at its peak, so the enzyme is used up

8. Use this

   Enzyme drawing (model, not to scale).

10. 6.

    Milo reads that an enzyme is a catalyst. Which sentence tells what a catalyst does?

    • It speeds up a reaction and turns into a product
    • It is a tiny living helper that works on its own
    • It supplies the energy that the reaction releases
    • It speeds up a reaction and is not used up
11. 7.

    Pia reads that heat can denature an enzyme. What does denature mean here?

    Use the picture in question 6.

    • The enzyme splits into products and is used up by the heat
    • The enzyme, a tiny living thing, stops moving in the heat
    • The enzyme speeds up because it holds more energy from the heat
    • The enzyme’s shape changes, so the substrate no longer fits
12. 8.

    Ren graphs a model enzyme’s activity at different temperatures. At which temperature is the activity highest?

    • 70 °C, the hottest tested
    • 30 °C
    • 20 °C
    • 40 °C
13. 9.

    Use Tala’s graph of a second model enzyme. What is its activity at 40 °C?

    • 20
    • 100
    • 60
    • 70
14. 10.

    Zee reads a third model enzyme’s graph. What happens to its activity as the temperature rises from 50 °C to 70 °C?

    • It stays at 100, because the enzyme adjusts like a living thing
    • It falls, because heat changes the enzyme’s shape
    • It keeps rising, because more heat means more speed
    • It falls, because the heat uses up the enzyme