Enzymes: how they speed reactions, and what pH and temperature do
Grade 9 Science Worksheet
Circle the best answer.
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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. Molecule M3: a square bead joined to a square bead.
Enzyme E has an active site shaped for a round bead joined to a square bead. Which molecule can Ari’s enzyme E work on?
- Molecule M1, because its beads match the active site
- Molecule M2, because a triangle bead is a better fit than a square
- Molecule M2, because it shares a round bead with the active site
- Molecule M3, because enzymes work on any molecule they touch
Two digestive enzymes (real data, from OpenStax Biology)
enzyme works in substrate it breaks down pepsin stomach protein salivary amylase mouth starch Pepsin works on proteins in the stomach. Bo wonders what pepsin does if it meets a starch molecule. Use the table.
- Pepsin splits the starch, and then pepsin is used up
- Nothing happens, because starch does not fit pepsin’s active site
- Pepsin breaks the starch down, because enzymes work on any food molecule
- Pepsin breaks the starch down, because stomach acid supplies the energy
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 N2, because its three beads match in order
- Molecule N3, because it has the same number of beads
- Molecule N1, because two matching beads is close enough
- Molecule N4, because the enzyme reshapes to fit anything
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 stays at 100, because the enzyme is alive and adjusts
- Activity rises, because more heat makes reactions faster
- Activity falls, because the heat changes the enzyme’s shape
- Activity falls, because the heat uses the enzyme up
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 100, because the added liquid supplies extra energy to the reaction
- Near 0, because pH 7 is far outside the enzyme’s best range
- Near 0, because pH 7 uses up the enzyme
- Near 100, because a neutral pH is gentler on most enzymes
Milo reads an energy diagram for one reaction with and without an enzyme. What is the activation energy with the enzyme?
- 60 energy units
- 95 energy units
- 55 energy units
- 20 energy units
Using Noah’s energy diagram, by how much does the enzyme lower the activation energy?
- 50 energy units
- 15 energy units
- 45 energy units
- 35 energy units
Ren tests two model enzymes, X and Y, across temperatures. Which is more active at 60 °C, and why?
- Enzyme Y, because it is alive and gets used to the heat
- Enzyme X, because it is the stronger of the two enzymes
- Enzyme X, because more heat speeds up an enzyme
- Enzyme Y, because 60 °C is close to its best temperature
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, because the acid supplies the energy it needs
- Enzyme Q, because its ideal pH is close to neutral, like water
- Enzyme P, but stomach acid will use it up
- Enzyme P, because it is most active near pH 2
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 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 stops working, because the stomach’s acid is far from the pH it needs
- It keeps working the same, because acid does not affect enzymes
- It starts working on protein, because enzymes fit any substrate
- It speeds up, because the acid adds energy