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 M3, because enzymes work on any molecule they touch
- Molecule M2, because it shares a round bead with the active site
- Molecule M2, because a triangle bead is a better fit than a square
- Molecule M1, because its beads match the active site
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 breaks the starch down, because stomach acid supplies the energy
- Nothing happens, because starch does not fit pepsin’s active site
- Pepsin splits the starch, and then pepsin is used up
- Pepsin breaks the starch down, because enzymes work on any food molecule
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 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
Milo reads an energy diagram for one reaction with and without an enzyme. What is the activation energy with the enzyme?
- 55 energy units
- 95 energy units
- 20 energy units
- 60 energy units
Using Noah’s energy diagram, by how much does the enzyme lower the activation energy?
- 50 energy units
- 15 energy units
- 35 energy units
- 45 energy units
Which statement describes what the enzyme does to Pia’s energy diagram?
- It lowers the peak from 110 to 75, and then the enzyme is used up
- 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
Ren tests two model enzymes, X and Y, across temperatures. Which is more active at 60 °C, and why?
- Enzyme Y, because 60 °C is close to its best temperature
- Enzyme X, because it is the stronger of the two enzymes
- Enzyme Y, because it is alive and gets used to the heat
- Enzyme X, because more heat speeds up an enzyme
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 it is most active near pH 2
- Enzyme P, but stomach acid will use it up
- Enzyme Q, because its ideal pH is close to neutral, like water
- Enzyme P, because the acid supplies the energy it needs
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 starts working on protein, because enzymes fit any substrate
- It speeds up, because the acid adds energy
- It keeps working the same, because acid does not affect enzymes