Step-by-Step Guidance for Photosynthesis Study Questions

Q1. Using the overall chemical reaction for photosynthesis, answer the following questions:

6 CO2 + 6 H2O + light → C6H12O6 + 6 O2

• a) Where in the cell is each of the input molecules used?

• b) For what purpose is each of the input molecules used?

• c) Where in the cell is each of the output molecules produced?

• d) Why is each of the output molecules produced?

Background

Topic: Photosynthesis – Inputs, Outputs, and Cellular Locations

This question tests your understanding of the overall process of photosynthesis, including where reactants are used and products are formed within the chloroplast, and the roles of these molecules.

Key Terms and Concepts:

• Chloroplast: Organelle where photosynthesis occurs.

• Thylakoid membrane: Site of light reactions.

• Stroma: Site of the Calvin cycle.

• Inputs: CO2, H2O, light energy.

• Outputs: Glucose (C6H12O6), O2.

Step-by-Step Guidance

1. Identify where each input molecule (CO2, H2O, light) enters the chloroplast and which part of the organelle uses it. Consider the stroma and thylakoid membrane.

2. Determine the role of each input: For example, is it a source of electrons, carbon, or energy?

3. Locate where each output molecule (glucose, O2) is produced within the chloroplast. Think about which reactions generate these products.

4. Explain the biological significance of each output: Why does the plant produce glucose and oxygen?

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Q2. Photosynthesis is a collaboration between the light reactions and the Calvin cycle. Answer the following questions about these metabolic reactions:

• a) How much ATP is consumed by photosynthesis?

• b) Where is ATP used?

• c) For what purpose is ATP used?

• d) How much NADPH is consumed by photosynthesis?

• e) Where is NADPH used?

• f) For what purpose is NADPH used?

Background

Topic: Energy and Electron Carriers in Photosynthesis

This question focuses on the roles of ATP and NADPH in the light reactions and Calvin cycle, including where and why they are used.

Key Terms and Concepts:

• ATP: Adenosine triphosphate, energy currency of the cell.

• NADPH: Electron carrier, provides reducing power.

• Calvin cycle: Uses ATP and NADPH to fix carbon.

Step-by-Step Guidance

1. Recall that ATP and NADPH are produced during the light reactions and consumed during the Calvin cycle.

2. Identify the steps of the Calvin cycle where ATP and NADPH are specifically used (e.g., reduction and regeneration phases).

3. Consider the stoichiometry: How many ATP and NADPH are required to produce one molecule of glucose?

4. Explain the purpose of ATP (energy input) and NADPH (reducing power) in the Calvin cycle.

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Q3. Light reactions:

• a) What pigments are used to capture sunlight energy? How are these pigments arranged to transfer captured light energy to non-pigment molecules?

• b) How are protons transferred across the thylakoid membrane? In which direction does this movement occur? Why is this movement important?

Background

Topic: Light Reactions – Pigments and Proton Gradient

This question examines your understanding of the roles of pigments in capturing light and the mechanisms of proton movement during the light reactions.

Key Terms and Concepts:

• Chlorophyll a, chlorophyll b, carotenoids: Main pigments.

• Photosystems: Complexes that organize pigments.

• Proton gradient: Created across the thylakoid membrane.

• ATP synthase: Uses the proton gradient to make ATP.

Step-by-Step Guidance

1. List the main pigments involved in light absorption and describe their arrangement in the light-harvesting complexes of photosystems.

2. Explain how energy is transferred from pigment to pigment and eventually to the reaction center.

3. Describe how the electron transport chain moves protons from the stroma into the thylakoid lumen, creating a proton gradient.

4. Discuss why the direction of proton movement is important for ATP synthesis.

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Q4. Calvin cycle:

• a) What are the 3 phases of the Calvin cycle? What does each phase accomplish?

• b) What is the major synthetic product of the Calvin cycle? How is it utilized by plant cells?

• c) For each molecule of glucose created by a plant cell, how many molecules of CO2 are “fixed?” How many molecules of O2 are produced?

Background

Topic: Calvin Cycle – Phases, Products, and Stoichiometry

This question tests your knowledge of the steps of the Calvin cycle, its products, and the relationship between carbon fixation and oxygen production.

Key Terms and Concepts:

• Phases: Carbon fixation, reduction, regeneration.

• G3P: Glyceraldehyde 3-phosphate, main product.

• Stoichiometry: Relationship between CO2 fixed and O2 produced.

Step-by-Step Guidance

1. Name and briefly describe each phase of the Calvin cycle and its main outcome.

2. Identify the main carbohydrate product and explain how it is used by the plant (e.g., for energy, storage, or structure).

3. Relate the number of CO2 molecules fixed to the number of glucose molecules produced, using the overall photosynthesis equation.

4. Connect the production of O2 to the splitting of water during the light reactions.

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Q5. Be able to trace the movements of high-energy electrons, protons, and carbon molecules through the light reactions and the Calvin cycle.

Background

Topic: Electron, Proton, and Carbon Flow in Photosynthesis

This question asks you to integrate your understanding of how energy and matter move through the stages of photosynthesis.

Key Terms and Concepts:

• Electron transport chain

• Proton gradient

• Carbon fixation

• NADP+/NADPH

• ATP synthase

Step-by-Step Guidance

1. Start by identifying the source of high-energy electrons (e.g., water) and follow their path through photosystem II, the electron transport chain, and photosystem I.

2. Describe how the movement of electrons is coupled to the movement of protons across the thylakoid membrane, creating a proton gradient.

3. Explain how ATP and NADPH produced in the light reactions are used in the Calvin cycle to fix carbon from CO2 into organic molecules.

4. Trace the fate of carbon atoms from CO2 through the Calvin cycle to the formation of glucose.

Try solving on your own before revealing the answer!