- 8.1 An Overview of Energy Cycling
- At this very moment, millions of plants are carrying out the process of photosynthesis and millions of humans are eating food. Despite their obvious differences, explain how both of these events demonstrate the first law of thermodynamics.
- Humans and other mammals eat food in order to have enough energy to move, communicate and carry out other life processes. We also maintain nearly constant body temperature. Use both the first and second laws of thermodynamics to explain how mammals can “generate” their own body heat.
- Pythons might only eat once a week, but hyenas hunt daily. Use the two laws of thermodynamics to explain why hyenas eat so much compared to reptiles.
- List the reactants and products for the process of photosynthesis. List the reactants and products for cellular respiration. Describe the relationship between these processes.
- Although photosynthesis and respiration take place as reactions among molecules inside cells, explain how these two processes also sustain food chains and ecosystems.
- A tiger eats a deer, which fed on plants. Describe the energy transformations in this short food chain. Explain why food chains cannot be longer than 4 or 5 steps.
- 8.2 Storing and Releasing Energy
- Describe what happens during chemical reactions.
- Explain how molecules can store energy.
- Explain the role of activation energy in the burning of methane. What would happen if you had a tank of methane, but no source of activation energy?
- Explain the differences between endergonic and exergonic reactions. First, state which reactions release and which store energy. Second, compare the chemical potential energy of the reactants and products in both types of reactions. (Using terms like “high energy products” and “low energy reactants” is sufficient.)
- Can an endergonic reaction provide the energy to drive an exergonic reaction? Explain why or why not. Use the first law of thermodynamics to help explain your answer.
- Can two endergonic reactions form a pair of coupled reactions? Use the first law of thermodynamics to help explain your answer.
- Describe two different events that might occur when an atom or molecule is oxidized. Describe what happens during reduction.
- 8.3 Photosynthesis: Using the Sun’s Energy
- Besides plants, what other organisms can carry out photosynthesis?
- Describe exactly where the reactions of photosynthesis occur in a plant.
- Energy occurs in many forms, such as heat energy, electrical energy, chemical energy, etc. Which forms of energy are involved in the process of photosynthesis?
- Take a look at Figure 8.13 in your text. Suppose a plant cell experienced a change in the Pc molecule of Photosystem II, so it could no longer be held within the thylakoid membrane. Speculate what would happen to this plant’s ability to carry out photosynthesis.
- Describe the specific role of light energy in photosynthesis. If the light energy cannot be destroyed, where does it go?
- At the beginning of Photosystem II, light energy boosts the energy level of a pair of electrons. At the end of Photosystem I, these electrons are used to reduce the molecule NADP+ to NADPH+H+. At which point do these electrons have the greatest potential energy?
- Using the first law of thermodynamics, explain the events of the light-dependent reactions of photosynthesis.
- Do the electrons that reduce molecule Pc in Photosystem II have more or less energy than the electrons that reduce molecule Pq? Use the second law of thermodynamics to support your answer.
- What are the names of the two energy-carrying molecules produced during the light-dependent reactions of photosynthesis?
- Look at Figure 8.14 in your text. In step 5, ATP and NADPH are used to form PGAL from PGA. (Don’t worry about the exact names or details of this process.) At this step, we can see three reactions occurring: 1) 12 ATP --> 12 ADP; 2) 12 NADPH --> 12 NADP; and 3) 12 PGA --> 12 PGAL. Which of these processes are endergonic and which are exergonic?
Study the Calvin cycle illustration in Figure 8.14 and read through the short section titled Light-Independent Reactions beginning on page 238 of your text. The 5-carbon sugar RuBP combines with CO2, and the chemical products are later zapped by energy released from ATP and NADPH. Yet at the end of the Calvin cycle, RuBP is produced again. This is where we started!
- If energy cannot be destroyed, where did the energy from the ATP and NADPH go?
- If energy cannot be created, where did the ATP and NADPH get their energy from?
- Compare and contrast the ways C4 and CAM plants fix CO2 in ways that help them conserve water.
- 8.4 Cellular Respiration
- Which organelle is the site of oxidative cellular respiration?
Glycolysis is a collection of nine separate reactions, each of which is catalyzed by a different enzyme. (See Figure 8.18 for details.)
- Looking at the overall results of the nine reactions of glycolysis, identify the initial reactant. What chemical is the final product?
- Using the second law of thermodynamics, let us compare the potential energy content of glucose and pyruvate. Predict which of these chemicals should have more potential energy. Explain your reasons.
- What would happen to the process of glycolysis if oxygen were not present?
- Pyruvate is the product of glycolysis, but acetyl enters the Krebs cycle. What happens in between?
At the beginning of the Krebs cycle, a 2-carbon acetyl molecule combines with a 4-carbon OAA (oxaloacetate) to form a 6-carbon citrate molecule. Yet after many steps, we end up with OAA again.
- What happens to the carbon and other atoms of the acetyl molecule?
- What happens to the energy that held acetyl and citrate together at the beginning of the cycle?
The final steps of cellular respiration involve an electron transport system resembling Photosystems II and I in photosynthesis.
- Make a list of similarities between these two electron transport systems. List the differences you can identify between them.
- We often associate the word respiration with the process of breathing. Where does oxygen ultimately fit into the process of cellular respiration?
- 8.5 Alternate Energy Pathways
- In humans, when do our cells switch to lactate fermentation?
- Identify the source of electrons and H+ to form lactate in animal cells during fermentation.
- Identify at least two similarities and two differences between lactate and alcohol fermentation.
- Describe how the anatomical structure of fast and slow twitch muscles allows each to function under different conditions. Cite examples from both birds and humans in your answer.
- Briefly describe at least three unique metabolic processes found only in bacteria.