Week 2 Experiment Answer Sheet: Experiments 1A, 1B, And 2 ✓ Solved

Week 2 Experiment Answer Sheet: Experiments 1A, 1B, and 2. I

Week 2 Experiment Answer Sheet: Experiments 1A, 1B, and 2. Perform the following activities using the Bioman Enzymatic Procedure A simulation and the Cellular Respiration and Photosynthesis setup. For each exercise, identify independent and dependent variables, describe observed relationships, provide specific results and explanations, and cite sources.

Experiment 2 Exercise 1A — Effect of temperature on enzyme function (use the Bioman enzymatic simulation). Questions: (1) Identify the dependent and independent variables. (2) Describe the relationship between temperature and enzyme activity. (3) State the temperature at which enzyme activity was highest. (4) Explain what happens when temperature becomes too high (cite sources). (5) Explain what happens when temperature becomes too low (cite sources).

Experiment 2 Exercise 1B — Effect of pH on enzyme function (continue in the Bioman simulation). Questions: (1) Identify the dependent and independent variables. (2) Describe the relationship between pH and enzyme activity and state the pH at which optimum activity occurred. (3) Explain the results based on enzyme structure and factors affecting function and cite your source.

Experiment 2 Exercise 2 — Cellular Respiration and Photosynthesis. Predict results based on the experimental setup using test tubes in dark and light with combinations of snails and Elodea. Use the CO2 indicator color code: Blue = no CO2, Green = medium CO2, Yellow = high CO2. Complete Table 3 predicted results for tubes 1D–4D (dark) and 1L–4L (light) and explain each prediction. Answer these questions: (1) Which treatment(s) showed the greatest CO2 and why? (2) Which treatment(s) showed the least CO2 and what happened to the CO2 present? (3) Were there differences between tubes 3D and 3L and why? (4) How do results show that snails produce CO2? (5) What was the purpose of tubes 1D and 1L (controls)?

Paper For Above Instructions

Overview

This paper summarizes observations, predicted outcomes, and mechanistic explanations for three Week 2 experiments: (1) the effect of temperature on enzyme activity, (2) the effect of pH on enzyme activity, and (3) the interaction of photosynthesis and cellular respiration in an aquatic microcosm. Simulations from the Bioman Enzymatic Procedure A and a simple tube experiment with snails and Elodea are used as the basis for predictions and interpretation (Bioman, no date).

Experiment 1A — Temperature and Enzyme Activity

Independent variable: temperature. Dependent variable: enzyme activity (reaction rate/product formation).

Relationship: Enzyme activity typically increases with temperature up to an optimum because higher temperatures raise molecular kinetic energy and collision frequency between enzyme and substrate. Beyond the optimum, activity declines sharply as protein tertiary structure is disrupted and the active site is deformed (denaturation) (Alberts et al., 2015; Berg et al., 2002).

Observed/typical optimum: Many mesophilic enzymes reach maximum activity near physiological temperature (~37°C). In the Bioman simulation, peak activity commonly appears at a middle-range temperature consistent with physiological optima (Bioman, no date). Thermostable enzymes from thermophiles have higher optima, whereas psychrophilic enzymes peak at lower temperatures (Somero, 1995).

High temperature effects: At temperatures above the enzyme’s optimal range, thermal energy breaks noncovalent bonds (hydrogen bonds, ionic interactions, hydrophobic packing) that maintain tertiary structure. Loss of structure alters the active site geometry and substrate binding, causing irreversible loss of catalytic activity (denaturation) (Fersht, 1999; Lehninger, Nelson & Cox, 2008).

Low temperature effects: At low temperatures enzyme structure remains mostly intact, but reduced kinetic energy lowers substrate diffusion and collision frequency with active sites; catalytic turnover (kcat) decreases. This effect is typically reversible: warming restores activity because the protein fold is preserved (Voet & Voet, 2011).

Experiment 1B — pH and Enzyme Activity

Independent variable: pH. Dependent variable: enzyme activity.

Relationship and optimum: Enzyme activity shows a bell-shaped dependence on pH. Each enzyme has an optimal pH at which charged amino acid residues in the active site and substrate are in the correct ionization states for binding and catalysis. For many cytosolic enzymes the optimum is near neutral (pH ~7), whereas gastric enzymes (e.g., pepsin) are optimized for strongly acidic conditions (pH ~2) (Campbell & Reece, 2014; Berg et al., 2002). In the Bioman simulation, optimum activity often corresponds to the pH that maintains the active-site ionization state required for catalysis (Bioman, no date).

Mechanistic explanation: pH alters the protonation state of ionizable side chains (e.g., His, Asp, Glu, Lys) that may participate in substrate binding or acid–base catalysis. Deviations from the optimum change charges, disrupt hydrogen bonding networks and salt bridges, and can induce conformational changes that lower activity or cause denaturation at extremes (Alberts et al., 2015; Lehninger et al., 2008).

Experiment 2 — Cellular Respiration and Photosynthesis Predictions

Setup summary: Two racks of tubes (D = dark, L = light) each containing combinations of snails and Elodea; CO2 indicator initial color = Green (medium). Blue = no CO2, Green = medium CO2, Yellow = high CO2.

Predicted Table 3 End Colors and Explanations

• 1D (0 snails, 0 Elodea, dark): Blue — no organisms to produce CO2, indicator should show no CO2.
• 2D (1 snail, 0 Elodea, dark): Yellow — snail respires in the dark, producing CO2 with no photosynthesis to consume it, so CO2 increases to high levels.
• 3D (0 snails, 1 Elodea, dark): Yellow/Green tending to Yellow — Elodea in the dark cannot photosynthesize and will respire, releasing CO2; CO2 level will rise (likely Yellow).
• 4D (1 snail, 1 Elodea, dark): Yellow (high) — both organisms respire without photosynthesis, producing high CO2; combined respiration gives the greatest CO2 accumulation.
• 1L (0 snails, 0 Elodea, light): Blue — no organisms; indicator remains at no CO2.
• 2L (1 snail, 0 Elodea, light): Yellow — snail produces CO2 and with no plant in the tube to consume it, CO2 accumulates.
• 3L (0 snails, 1 Elodea, light): Blue — Elodea photosynthesizes in light, consuming CO2 and producing oxygen, which reduces CO2 to low/undetectable levels.
• 4L (1 snail, 1 Elodea, light): Green — snail respiration produces CO2 while Elodea photosynthesis consumes CO2; if rates are roughly balanced the result is an intermediate CO2 level (medium, Green). If photosynthesis outpaces respiration, color may trend Blue.

Questions and Explanations

(1) Greatest CO2: Dark tubes containing animals and/or plants that only respire (2D, 3D, 4D) show the greatest CO2 because photosynthesis is suppressed and respiration produces CO2 continuously; 4D likely has the highest due to two organisms respiring (Wetzel, 2001).

(2) Least CO2: Light tubes containing only Elodea (3L) or empty tubes (1L) show the least CO2. In 3L CO2 produced by respiration is rapidly consumed by photosynthesis; in empty tubes there is minimal gas exchange and no respiration (Raven et al., 2005).

(3) Differences between 3D and 3L: Yes. 3D will accumulate CO2 because Elodea in dark respires; 3L will reduce CO2 because Elodea in light photosynthesizes and consumes CO2. This demonstrates the diurnal shift between net respiration (dark) and net photosynthesis (light) in plants (Campbell & Reece, 2014).

(4) Evidence that snails produce CO2: Tubes with snails but no plants (2D and 2L) show increased CO2 (yellow), indicating that animal metabolism releases CO2 as a byproduct of cellular respiration; the effect is observed regardless of light because snails respire continuously (Alberts et al., 2015).

(5) Purpose of tubes 1D and 1L: They serve as negative controls to show the baseline indicator response in the absence of biological CO2 sources or sinks; they allow attribution of color changes to organismal activity rather than to experimental artifacts.

Conclusions

Temperature and pH are critical determinants of enzyme activity: temperature modulates kinetic energy and stability while pH influences active-site ionization states. Enzymes have narrow optima beyond which activity declines due to reversible kinetic effects (low temperature) or irreversible denaturation (high temperature) (Fersht, 1999; Somero, 1995). The aquatic microcosm predictions illustrate the complementary roles of photosynthesis and respiration: photosynthetic organisms consume CO2 and produce O2 in the light, while all aerobic organisms produce CO2 continuously via respiration; light conditions therefore determine net changes in CO2 levels (Raven et al., 2005; Wetzel, 2001).

References

• Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2015). Molecular Biology of the Cell (6th ed.). Garland Science.
• Berg, J. M., Tymoczko, J. L., & Stryer, L. (2002). Biochemistry (5th ed.). W. H. Freeman.
• Lehninger, A. L., Nelson, D. L., & Cox, M. M. (2008). Lehninger Principles of Biochemistry (5th ed.). W. H. Freeman.
• Voet, D., & Voet, J. G. (2011). Biochemistry (4th ed.). John Wiley & Sons.
• Campbell, N. A., & Reece, J. B. (2014). Biology (10th ed.). Pearson.
• Raven, P. H., Evert, R. F., & Eichhorn, S. E. (2005). Biology of Plants (7th ed.). W. H. Freeman.
• Wetzel, R. G. (2001). Limnology: Lake and River Ecosystems (3rd ed.). Academic Press.
• Fersht, A. (1999). Structure and Mechanism in Protein Science: A Guide to Enzyme Catalysis and Protein Folding. W. H. Freeman.
• Somero, G. N. (1995). Proteins and temperature. Annual Review of Physiology, 57, 43–68.
• Bioman Biology. (no date). Enzymes—Enzymatic Procedure A (online simulation). Bioman Biology. https://www.biomanbio.com/