Chapter 5: Energy and Enzymes
What is the difference between kinetic and potential energy?
Kinetic energy is the energy of motion. Potential energy is stored energy due to position or structure.
What is the function of the mesophyll and stomata in a leaf?
Mesophyll = cells where photosynthesis occurs. Stomata = pores that allow CO₂ in and O₂/water vapor out.
Which bond in ATP is typically broken to release usable energy?
The bond between the last phosphate group (terminal phosphate) is broken — the phosphoanhydride bond.
Is cellular respiration exergonic or endergonic?
Cellular respiration is exergonic because it releases energy by breaking down glucose.
Identify the reactants and products of the light reactions and where they occur.
Reactants: light, water, ADP, NADP⁺ Products: ATP, NADPH, O₂ Location: thylakoid membranes.
Where does glycolysis occur, and what are its initial reactants and final products?
Location: cytosol Reactants: glucose, 2 ATP Products: 2 pyruvate, 2 ATP (net), 2 NADH
Define Gibbs free energy (∆G) and explain what a positive versus negative ∆G indicates.
Gibbs free energy = usable energy available to do work. Positive ∆G = reaction requires energy (endergonic). Negative ∆G = reaction releases energy (exergonic, spontaneous).
Describe the Z‑scheme and how it results in the production of ATP and NADPH.
The Z‑scheme describes electron flow from Photosystem II → ETC → Photosystem I, producing ATP (from the proton gradient) and NADPH (from reduction at PSI).
Explain how the electron transport chain creates a proton gradient, and identify the enzyme that uses this gradient to synthesize ATP.
Electrons move through ETC proteins → energy pumps H⁺ into intermembrane space → gradient powers ATP synthase, which makes ATP.
Explain how competitive and noncompetitive inhibitors differ in how they affect enzyme activity.
Competitive inhibitors bind the active site and can be overcome by adding more substrate. Noncompetitive inhibitors bind an allosteric site, changing enzyme shape; adding substrate does NOT overcome inhibition.
Trace the path of energy from light, through the light reactions and Calvin cycle, to the formation of glucose. Include the major intermediates.
Light excites electrons → ATP & NADPH made in light reactions → ATP & NADPH power the Calvin cycle → carbon fixation → G3P → glucose.
A poison blocks the final electron acceptor in the ETC. Predict what happens to the H+ gradient and ATP production.
If electrons cannot reach oxygen: • ETC stops • H⁺ gradient collapses • ATP production by oxidative phosphorylation stops
A reaction has a positive ∆G and will not proceed spontaneously. Explain how a cell can make this reaction occur using ATP coupling, and describe what happens energetically.
A positive ∆G reaction is endergonic. Cells make it occur by coupling it to ATP hydrolysis, which releases enough energy (negative ∆G) to drive the reaction forward.
Heavy oxygen isotope–labeled water is given to a plant. Predict which product of photosynthesis will contain the labeled oxygen and explain why based on the steps of the light reactions.
The labeled oxygen from H₂O ends up in O₂ gas, because water is split during the light reactions and its oxygen atoms are released as oxygen gas.
A muscle cell becomes oxygen‑limited during intense exercise. Explain how it keeps glycolysis running, what product is formed, and compare its ATP yield to aerobic respiration.
Muscle uses lactic acid fermentation. Pyruvate → lactate to regenerate NAD⁺ → glycolysis continues. ATP yield = 2 ATP per glucose, far less than aerobic respiration (~30–32 ATP).