BIOL 241 Exam Review: Bioenergetics, Respiration, Photosynthesis and Ecosystem Energy Flow

Terms in this set (32)

1. State the first law of thermodynamics and what it means for organisms.Energy cannot be created or destroyed, only converted from one form to another. Organisms do not make energy; they convert light or chemical energy into ATP, work and heat.
2. State the second law of thermodynamics and what it means for living systems.Every energy conversion increases the total entropy of the universe, and some energy is lost as heat. Organisms stay highly ordered only by taking in energy constantly and releasing heat and disorder to their surroundings.
3. Gibbs free energy equation and its symbolsΔG = ΔH - TΔS. ΔG is the change in free energy, ΔH the change in enthalpy (heat content), T the absolute temperature in kelvin and ΔS the change in entropy. A negative ΔG means the reaction is spontaneous.
4. How does ΔG differ from the standard value ΔG°'?ΔG°' applies under standard conditions (1 M concentrations, pH 7). The actual ΔG = ΔG°' + RT ln Q depends on cell concentrations, so a reaction with a positive ΔG°' can still proceed if products are kept low.
5. How do cells drive endergonic reactions?By coupling them to exergonic reactions, usually ATP hydrolysis, so the combined ΔG is negative. Often a phosphate is transferred from ATP to a reactant, creating a more reactive intermediate.
6. Why is ATP a useful energy currency?Hydrolysis of its terminal phosphoanhydride bond releases a convenient amount of free energy (ΔG°' about -30.5 kJ/mol). ATP is quickly regenerated from ADP + Pi by respiration or photosynthesis.
7. Define oxidation and reduction, and give the role of NAD+.Oxidation is loss of electrons and reduction is gain of electrons (OIL RIG). NAD+ is reduced to NADH by accepting electrons (with H+) from food molecules, then carries those electrons to the electron transport chain.
8. What is the induced fit model of enzyme action?When the substrate binds, the active site changes shape slightly to grip it more tightly. This strains bonds and stabilizes the transition state, lowering the activation energy.
9. What does Km mean in Michaelis-Menten kinetics?Km is the substrate concentration at which the reaction rate is half of Vmax. A low Km means high affinity: the enzyme reaches half speed at a low substrate concentration.
10. What is feedback inhibition? Give a respiration example.The end product of a pathway inhibits an earlier enzyme, often allosterically, to prevent overproduction. High ATP and citrate inhibit phosphofructokinase (PFK), the key regulatory enzyme of glycolysis.
11. How do temperature and pH affect enzyme activity?Activity rises with temperature up to an optimum, then drops sharply as the enzyme denatures. Each enzyme also has an optimal pH; values far from it change the charges on R groups and disrupt the enzyme's shape.
12. Describe the two phases of glycolysis.Energy investment phase: 2 ATP are used to phosphorylate glucose and split it into two 3-carbon sugars. Payoff phase: 4 ATP and 2 NADH are produced, for a net gain of 2 ATP per glucose.
13. Substrate-level phosphorylation vs oxidative phosphorylationSubstrate-level: an enzyme transfers a phosphate directly from a substrate to ADP (in glycolysis and the citric acid cycle). Oxidative: ATP synthase makes ATP using the proton gradient produced by the electron transport chain.
14. About how many ATP does aerobic respiration yield per glucose, and where do most come from?About 30 to 32 ATP. Most come from oxidative phosphorylation powered by NADH and FADH2 (about 2.5 ATP per NADH and 1.5 per FADH2).
15. Why is oxygen essential for aerobic respiration, and how does cyanide kill?O2 is the final electron acceptor at the end of the electron transport chain, forming water. Cyanide blocks complex IV (cytochrome c oxidase), so electron flow, proton pumping and ATP synthesis stop.
16. What do uncoupling proteins do, for example in brown fat?They let H+ leak back across the inner mitochondrial membrane without passing through ATP synthase. The gradient's energy is released as heat instead of making ATP, which is how brown fat produces heat (non-shivering thermogenesis).
17. Anaerobic respiration vs fermentationAnaerobic respiration still uses an electron transport chain but with a final electron acceptor other than O2 (for example sulfate or nitrate). Fermentation uses no electron transport chain; it only regenerates NAD+ and makes 2 ATP per glucose.
18. How are fats used for energy, and why do they store so much?Triglycerides are broken into glycerol and fatty acids; beta-oxidation cuts the fatty acids into acetyl CoA for the citric acid cycle. Fats are highly reduced, so they yield about 9 kcal/g compared with about 4 kcal/g for carbohydrate or protein.
19. Photoautotroph vs chemoautotroph vs heterotrophPhotoautotrophs make organic molecules from CO2 using light. Chemoautotrophs make them from CO2 using energy from oxidizing inorganic chemicals (such as H2S at deep-sea vents). Heterotrophs get both energy and carbon by eating organic matter.
20. Why do plants look green, and what does an action spectrum show?Chlorophyll absorbs mainly blue and red light and reflects green. An action spectrum plots photosynthetic rate against wavelength, showing which wavelengths actually drive photosynthesis.
21. What are the roles of photosystem II and photosystem I in the light reactions?PSII uses light to energize electrons, replacing them by splitting water, which releases O2. Its electrons pass down a transport chain that pumps H+ for ATP. PSI re-energizes the electrons to reduce NADP+ to NADPH.
22. What is cyclic electron flow, and why do chloroplasts use it?Electrons from PSI cycle back to the electron transport chain instead of reducing NADP+. This makes extra ATP but no NADPH and no O2, balancing the Calvin cycle's higher demand for ATP.
23. Calvin cycle: what does it take to make one G3P?Three turns, fixing 3 CO2, use 9 ATP and 6 NADPH and produce one net G3P (a 3-carbon sugar). The cycle has three stages: carbon fixation by rubisco, reduction, and regeneration of RuBP.
24. What is photorespiration, and when does it occur?Rubisco binds O2 instead of CO2, which wastes energy and releases fixed carbon as CO2. It increases in hot, dry conditions, when stomata close and the O2:CO2 ratio inside the leaf rises.
25. C4 vs CAM plantsBoth fix CO2 first with PEP carboxylase, which does not bind O2, to reduce photorespiration. C4 plants (such as corn) separate the steps in space between mesophyll and bundle sheath cells. CAM plants (such as cacti) separate them in time: they open stomata at night and run the Calvin cycle by day.
26. Gross vs net primary productivityGPP is the total rate at which producers capture energy by photosynthesis. NPP = GPP - the energy producers use in their own respiration. NPP is the energy available to consumers.
27. Roughly what fraction of energy passes from one trophic level to the next, and why?About 10%, though it ranges from about 5 to 20%. Most energy is lost as heat from respiration, or is never eaten, digested or assimilated.
28. Why are food chains usually short, and why is a pyramid of energy never inverted?With only about 10% transferred at each step, too little energy remains to support more than about 4 or 5 trophic levels. Each level must have less energy than the level below it, so energy pyramids always narrow upward.
29. Endotherm vs ectothermEndotherms (mammals, birds) keep body temperature high mainly with metabolic heat, which needs high energy intake. Ectotherms (most reptiles, fish, invertebrates) rely mainly on external heat, so they need much less food for their size.
30. How does metabolic rate scale with body mass?Basal metabolic rate scales roughly with M^0.75 (Kleiber's law). So mass-specific metabolic rate (per gram) falls as body size rises: a mouse burns far more energy per gram than an elephant.
31. Why do small animals lose heat faster for their size?They have a higher surface area to volume ratio, so more surface is available for heat loss relative to the tissue that produces heat.
32. Write the basic energy budget of an animal.Ingested energy = egested energy (feces) + assimilated energy. Assimilated energy = energy used in respiration (maintenance and activity, lost as heat) + production (growth and reproduction).