From Light Energy to Glucose: The Chloroplast Pathway

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Part 1: Chloroplast Pathway and Key Terms

Directions: Use the word bank to complete the pathway labels and definitions. Some terms may be used more than once.

Word Bank: chloroplast, thylakoid, granum, stroma, chlorophyll, light-dependent reactions, electron transport chain, ATP, NADPH, Calvin cycle, carbon dioxide, glucose

1. Complete the pathway diagram by filling in the blanks.

Sunlight → __________ and __________ located in the ____________________ → ____________________ → __________ and __________

H₂O enters: ______________________________ O₂ leaves: ______________________________

__________ enters the stroma → ____________________ in the stroma → ____________________

2. Match each structure or molecule with its best description.

A. Chloroplast

B. Thylakoid

C. Stroma

D. Chlorophyll

E. ATP

F. NADPH

1. Green pigment that absorbs light energy

2. Fluid-filled region surrounding the thylakoids

3. Energy-carrying molecule used in cell reactions

4. Organelle where photosynthesis occurs

5. Membrane sac containing photosystems

6. Electron carrier that provides high-energy electrons and hydrogen

3. What is a granum, and how is it related to a thylakoid?

4. Define the Calvin cycle in your own words. Include its location in the chloroplast.

Part 2: Energy, Inputs, Outputs, and Evidence

5. Which process directly captures light energy?

The Calvin cycle

The light-dependent reactions

Glucose breakdown

Carbon dioxide diffusion

6. Put these events in the correct order by numbering them 1–4.

_____ The Calvin cycle uses carbon dioxide to build carbohydrate.

_____ Light excites electrons in chlorophyll.

_____ ATP and NADPH carry energy to the stroma.

_____ The electron transport chain helps produce ATP and NADPH.

7. Identify the inputs and outputs of the light-dependent reactions.

Inputs: ________________________________________________________________

Outputs: _______________________________________________________________

8. Explain how ATP and NADPH connect the light-dependent reactions to the Calvin cycle.

9. Annotate the balanced photosynthesis equation. Circle the reactants, underline the products, and label where light energy is used.

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

Reactants: __________________________ Products: __________________________

Which product stores chemical energy? __________________________

10. Higher-order scenario: A plant is moved from bright light to very dim light. Predict what happens to ATP and NADPH production and to the Calvin cycle. Explain your reasoning.

Answer Key — Final Page

1. Sunlight → chlorophyll and photosystems located in the thylakoid membranes → electron transport chain → ATP and NADPH. H₂O enters the light-dependent reactions; O₂ leaves. Carbon dioxide enters the stroma → Calvin cycle in the stroma → glucose.

2. A–4, B–5, C–2, D–1, E–3, F–6.

3. A thylakoid is a membrane sac containing photosystems. A granum is a stack of thylakoids.

4. The Calvin cycle is a series of reactions that uses carbon dioxide, ATP, and NADPH to produce carbohydrate. It occurs in the stroma.

5. The light-dependent reactions.

6. Calvin cycle uses carbon dioxide: 4; light excites electrons: 1; ATP and NADPH carry energy: 3; electron transport chain produces ATP and NADPH: 2.

7. Inputs: light energy and water. Outputs: oxygen, ATP, and NADPH.

8. ATP supplies energy and NADPH supplies high-energy electrons and hydrogen to the Calvin cycle. They transfer energy captured during the light-dependent reactions to the reactions that build carbohydrate.

9. Reactants: 6CO₂, 6H₂O, and light energy. Products: C₆H₁₂O₆ and 6O₂. Glucose stores chemical energy. Light energy is used in the light-dependent reactions.

10. Dim light reduces the rate of the light-dependent reactions, so less ATP and NADPH are produced. The Calvin cycle slows because it has less ATP and NADPH available, which generally reduces glucose production.