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

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Model drawing, not to scale. Esme’s enzyme G holds three beads in a row: round, square, round. Which substrate fits it? Use the drawing.

   • Molecule N1, because two matching beads is close enough
   • Molecule N4, because the enzyme reshapes to fit anything
   • Molecule N2, because its three beads match in order
   • Molecule N3, because it has the same number of beads
2. 2.

   Jun warms a mixture holding the model enzyme in the graph from 40 °C to 60 °C. Predict the activity and choose the reason.

   • Activity falls, because the heat uses the enzyme up
   • Activity falls, because the heat changes the enzyme’s shape
   • Activity stays at 100, because the enzyme is alive and adjusts
   • Activity rises, because more heat makes reactions faster
3. 3.

   The model enzyme in the graph works best near pH 2. Kira changes the mixture to pH 7. Predict the activity and choose the reason.

   • Near 0, because pH 7 is far outside the enzyme’s best range
   • Near 100, because a neutral pH is gentler on most enzymes
   • Near 0, because pH 7 uses up the enzyme
   • Near 100, because the added liquid supplies extra energy to the reaction
4. 4.

   A mixture holds a fixed amount of enzyme. Luz raises the substrate from 5 to 7. Using the graph, predict the rate and the reason.

   • It stays near 90, because the active sites are full
   • It rises, because each extra substrate adds to the rate
   • It falls, because the extra substrate uses up the enzyme
   • It rises, because the extra substrate brings extra energy
5. 5.

   Milo reads an energy diagram for one reaction with and without an enzyme. What is the activation energy with the enzyme?

   • 55 energy units
   • 20 energy units
   • 95 energy units
   • 60 energy units
6. 6.

   Using Noah’s energy diagram, by how much does the enzyme lower the activation energy?

   • 45 energy units
   • 50 energy units
   • 15 energy units
   • 35 energy units
7. 7.

   Which statement describes what the enzyme does to Pia’s energy diagram?

   • It raises the end from 20 to 50, adding energy to the products
   • It raises the start from 50 to 75, so the reaction begins sooner
   • It lowers the peak from 110 to 75; the start and end stay at 50 and 20
   • It lowers the peak from 110 to 75, and then the enzyme is used up
8. 8.

   Ren tests two model enzymes, X and Y, across temperatures. Which is more active at 60 °C, and why?

   • Enzyme X, because more heat speeds up an enzyme
   • Enzyme X, because it is the stronger of the two enzymes
   • Enzyme Y, because it is alive and gets used to the heat
   • Enzyme Y, because 60 °C is close to its best temperature
9. 9.

   Tala knows the stomach’s pH is between 1.5 and 2.5. Which model enzyme, P or Q, suits the stomach, and why?

   • Enzyme P, but stomach acid will use it up
   • Enzyme P, because it is most active near pH 2
   • Enzyme Q, because its ideal pH is close to neutral, like water
   • Enzyme P, because the acid supplies the energy it needs

10. Read this first

    Where two enzymes work (real data, from OpenStax Biology and OpenStax Anatomy and Physiology)

    enzyme	works in	pH there
    pepsin	stomach	1.5 to 2.5
    salivary amylase	mouth	6.35 to 6.85

11. 10.

    Zee reads that salivary amylase has a working range of pH 6.35 to 6.85. Use the table. What happens to it in the stomach?

    • It starts working on protein, because enzymes fit any substrate
    • It keeps working the same, because acid does not affect enzymes
    • It speeds up, because the acid adds energy
    • It stops working, because the stomach’s acid is far from the pH it needs