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Photosynthesis worksheet: light reactions and the Calvin cycle

A free, printable worksheet for high school and AP Biology. Students follow light energy from chlorophyll through both photosystems to ATP and NADPH, track every carbon through the Calvin cycle, and compare photosynthesis with cellular respiration.

Download the PDF (free)Answer key (Teacher plan)

What's inside

  1. Vocabulary (10 terms)
  2. The big picture (2 questions)
  3. The light-dependent reactions (7 questions)
  4. Making ATP (3 questions)
  5. The Calvin cycle (5 questions)
  6. Photosynthesis and cellular respiration (3 questions)

Teach it with the 3D lesson

Every question matches a step in CytoTour's 3D chapter on photosynthesis, built from real spinach and pea protein structures at true size. Read the steps with pictures on photosynthesis, step by step, or project the lesson in class — Chapter 1 is free, and the Teacher plan opens every chapter.

The worksheet

This is the printable sheet (21 questions). Printing this page prints only the worksheet.

CytoTour · cytotour.com · free to print and copy for your classes

Photosynthesis

NameDatePeriod

Part 1 · Vocabulary

1. Write the letter of the matching description next to each term.

  1. Thylakoid
  2. Granum
  3. Stroma
  4. Chlorophyll
  5. Reaction center
  6. NADPH
  7. Chemiosmosis
  8. RuBisCO
  9. Carbon fixation
  10. G3P
  1. AThree-carbon product of the Calvin cycle; one leaves for every three CO₂ fixed
  2. BTurning inorganic CO₂ into organic molecules
  3. CProtons flowing back through ATP synthase drive the formation of ATP
  4. DThe enzyme that joins CO₂ to RuBP
  5. EPigment that absorbs blue and red light and reflects green
  6. FA stack of thylakoids
  7. GEnergy carrier made when photosystem I reduces NADP⁺
  8. HDisc-shaped membrane sac inside the chloroplast
  9. IThe fluid around the grana, where the Calvin cycle happens
  10. JWhere a special pair of chlorophyll a gives up an excited electron

Part 2 · The big picture

2. Write the overall equation for photosynthesis. What supplies the energy?

3. Complete the table for the two stages of photosynthesis.

Where in the chloroplastTakes inGives out
Light-dependent reactions
Calvin cycle

Part 3 · The light-dependent reactions

4. Why do most leaves look green?

  1. AChlorophyll absorbs green light best
  2. BChlorophyll absorbs blue and red light and reflects green
  3. CLeaves are full of green carotenoids
  4. DGreen light carries the most energy

5. In a photosystem's antenna, what is passed from chlorophyll to chlorophyll after a photon is absorbed, and where does it end up?

6. P680 in photosystem II has just given away an excited electron. Where does the electron that replaces it come from?

  1. AWater
  2. BOxygen gas
  3. CCarbon dioxide
  4. DNADPH

7. The O₂ that plants release — where do its oxygen atoms come from?

  1. AFrom water
  2. BFrom carbon dioxide
  3. CFrom glucose
  4. DThey are created from light energy

8. Put these in the order the electrons from water pass through them. Number them 1–6.

  1. NADP⁺
  2. Plastocyanin (Pc)
  3. Photosystem I (P700)
  4. Cytochrome b6f complex
  5. Photosystem II (P680)
  6. Plastoquinone (Pq)

9. Why do the electrons need a second photon at photosystem I?

10. Photosystem I energizes the electrons once more. Which molecule finally receives them?

  1. ANADP⁺, which becomes NADPH
  2. BO₂, which becomes water
  3. CADP, which becomes ATP
  4. DCO₂, which becomes sugar

Part 4 · Making ATP

11. During the light reactions, where is the pH lowest?

  1. AIn the thylakoid lumen
  2. BIn the stroma
  3. CIn the cytoplasm
  4. DIt is the same everywhere

12. Explain how the light reactions make ATP.

13. The chloroplast ATP synthase has 14 c-subunits; one full turn moves 14 protons and makes 3 ATP. About how many protons does each ATP take? The human mitochondrial enzyme moves 8 protons per turn — how many per ATP there?

Part 5 · The Calvin cycle

14. Complete the table for three turns of the Calvin cycle (three CO₂ fixed).

Molecules inMolecules outEnergy used
1 · Fixation
2 · Reduction
3 · Regeneration

15. One G3P (three carbons) leaves the Calvin cycle. How many CO₂ molecules had to be fixed to make it?

  1. A1
  2. B3
  3. C6
  4. D18

16. Show that carbon atoms are conserved in the fixation stage of three turns.

17. How many turns of the Calvin cycle does one glucose take? Why?

18. Why is "dark reactions" a misleading name for the Calvin cycle?

Part 6 · Photosynthesis and cellular respiration

19. Compare photosynthesis and cellular respiration.

PhotosynthesisCellular respiration
Organelle (in eukaryotes)
Takes in
Gives out
Electron transport chain in
ATP made by

20. Which statement is true?

  1. APlants photosynthesize instead of respiring
  2. BPlants carry out both photosynthesis and cellular respiration
  3. COnly animals carry out cellular respiration
  4. DOnly plants carry out photosynthesis

21. Which organisms first carried out photosynthesis, and how did they change Earth?