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

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Bo’s friend says an enzyme speeds a reaction by giving the substrate the energy it needs. Use the diagram. Which response is best?

   • Disagree: it lowers the activation energy, so less is needed
   • Agree: the enzyme stores energy and hands it to the reaction
   • Agree: the energy it supplies pushes the substrate over the hill
   • Disagree: it lowers the energy of the products instead

2. Read this first

   Use this

   Model drawing, not to scale. Enzyme E has a notch, its active site, shaped to hold a round bead joined to a square bead. Molecule M1: a round bead joined to a square bead. Molecule M2: a round bead joined to a triangle bead.

3. 2.

   Esme’s friend says enzymes are tiny living things, so one can learn to work on any substrate. Which response is best?

   • Agree: an enzyme is alive because it works inside living cells
   • Disagree: an enzyme is a protein, so it fits any substrate equally
   • Disagree: an enzyme is a protein whose active site fits a matching substrate
   • Agree: living enzymes reshape their active site to fit any substrate

4. Use the table

   Investigation card (model data; a teacher handles every chemical). Question: How does temperature affect catalase? What is changed: the temperature of the catalase solution. What is measured: the height of the oxygen foam after 1 minute. What stays the same: 5 mL of catalase solution and 5 mL of hydrogen peroxide in each tube.

   temperature (°C)	foam height (mm)
   10	8
   30	30
   50	12
   80	0

5. 3.

   A teacher ran this catalase test while Jun’s class watched. Which conclusion do the data support?

   • Catalase was used up at 80 °C, which is why no foam formed
   • 30 °C is exactly the best temperature for catalase
   • More heat gave more foam, so catalase works best above 80 °C
   • Among the four, 30 °C gave the most foam and 80 °C gave none
6. 4.

   Kira’s class reads a teacher’s catalase test. What is the flaw in the test?

   • The catalase in Tube 1 was used up, so the tubes cannot be compared
   • The hydrogen peroxide amount should have changed in each tube
   • Tube 2 should have been hotter, since heat speeds up enzymes
   • Two things changed at once: the temperature and the catalase amount
7. 5.

   A teacher added water to Tube 2 on purpose, while Luz’s class watched. What does Tube 2 help show?

   • Water stops foam from forming, since the water tube had none
   • Catalase turns into foam, since the water tube had none
   • Catalase supplies the energy, since the water tube had none
   • Catalase is what makes the foam form: water alone made none

8. Use this

   Rate-versus-substrate graph with and without inhibitor I (model data). Substrate amount (units) across, 0 to 7, a mark every 1. Reaction rate (units per minute) up, 0 to 100, a mark every 20. Enzyme alone joins (0 units, 0), (1 unit, 30), (2 units, 55), (3 units, 75), (4 units, 85), (5 units, 90), (6 units, 90), (7 units, 90) with straight pieces. Enzyme with inhibitor I joins (0 units, 0), (1 unit, 15), (2 units, 32), (3 units, 50), (4 units, 65), (5 units, 78), (6 units, 86), (7 units, 90) with straight pieces. A small drawing beside the graph shows inhibitor I, shaped like the substrate, sitting in the enzyme’s active site.

9. 6.

   Milo sees inhibitor I sit in the enzyme’s active site in the drawing. Using the graph at substrate 2, what does I do, and why?

   • The rate rises, because I adds energy to the active sites
   • The rate falls, because I changes the substrate’s shape
   • The rate falls, because I takes up active sites
   • The rate falls, because I uses up the enzyme over time
10. 7.

    Noah sees the two lines meet at 90 at substrate 7. Which explanation fits both the graph and the drawing of inhibitor I?

    • I changes into whatever substrate the enzyme fits
    • The extra substrate outcompetes I for active sites
    • I is used up by the extra substrate that arrives
    • The extra substrate brings energy that cancels I
11. 8.

    Pia knows inhibitor I fits enzyme E’s active site, not F’s. Using the drawing and the table, which statement is best?

    • I slows E but not F, because I matches E’s active site
    • I slows both, because an inhibitor blocks any enzyme it meets
    • I slows E by using E up, while F is left untouched
    • I speeds F up, because F has no matching active site for I
12. 9.

    Ren sees the model enzyme was more active at 40 °C than at 20 °C, but nearly stopped at 60 °C. Which explanation fits the whole graph?

    • The enzyme was used up between 40 °C and 60 °C, so rates fell
    • Heat speeds reactions, so the 60 °C reading must be a measuring error
    • The enzyme gave away its energy as it got hotter, so it slowed
    • Heat helps up to a point, then changes the enzyme’s shape
13. 10.

    In Tala’s test, the rate did not change when the substrate rose from 6 to 7. Which explanation fits the graph?

    • The substrate stopped fitting once there was more of it
    • The enzyme was used up by the extra substrate added at 7
    • The extra substrate brought energy that slowed the enzyme down
    • Nearly all active sites were already busy