Table of contents
- 1. Introduction to Biology2h 42m
- 2. Chemistry3h 37m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 44m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses19m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 6m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 53m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport1h 2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System1h 10m
- 40. Circulatory System1h 49m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System1h 4m
- 44. Animal Reproduction1h 2m
- 45. Nervous System1h 55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
7. Energy and Metabolism
Enzyme Activation Energy
Problem 6
Textbook Question
If you were to expose glucose to oxygen on your lab bench, why would you not expect to see it burn as described by the reaction in Figure 8.6?
a. The reaction is endergonic and requires an input of energy.
b. The reaction is not spontaneous unless an enzyme is added.
c. The sugar must first be phosphorylated to increase its potential energy.
d. Activation energy is required for the sugar and oxygen to reach their transition state.

1
Understand the chemical reaction: The reaction between glucose and oxygen is a redox reaction where glucose is oxidized to carbon dioxide and oxygen is reduced to water, releasing energy.
Identify the nature of the reaction: The reaction is exergonic, meaning it releases energy, as shown by the release of energy in the form of heat and light in the diagram.
Consider the role of activation energy: Even though the reaction is exergonic, it requires an initial input of energy to overcome the activation energy barrier, allowing the reactants to reach the transition state.
Recognize the need for a catalyst: In biological systems, enzymes act as catalysts to lower the activation energy, making the reaction proceed at a noticeable rate. Without an enzyme, the reaction would be too slow to observe under normal conditions.
Conclude why the reaction doesn't occur spontaneously on the lab bench: Without an enzyme or sufficient activation energy, the reaction between glucose and oxygen will not proceed spontaneously, which is why you wouldn't see it burn on the lab bench.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Activation Energy
Activation energy is the minimum energy required for a chemical reaction to occur. In the case of glucose burning in the presence of oxygen, this energy is necessary to initiate the reaction, allowing the reactants to reach a transition state where they can transform into products. Without sufficient activation energy, the reaction will not proceed, even if the reactants are present.
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Spontaneity of Reactions
A spontaneous reaction is one that occurs without the need for continuous external energy input. While the combustion of glucose is exothermic and releases energy, it is not spontaneous at room temperature without a catalyst or sufficient activation energy. Understanding the conditions under which a reaction becomes spontaneous is crucial for predicting its behavior in a lab setting.
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Endergonic vs. Exergonic Reactions
Endergonic reactions require an input of energy to proceed, while exergonic reactions release energy. The combustion of glucose is typically exergonic, but the initial activation energy needed to start the reaction can make it seem endergonic until that threshold is met. Recognizing the energy dynamics of these reactions helps clarify why glucose does not spontaneously ignite in the presence of oxygen.
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Related Practice
Multiple Choice
A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that __________.
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