The overall equation for photosynthesis is

Answer: 6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂ Carbon fixation + water splitting drives glucose production and oxygen release.

The "dark reactions" / "light-independent reactions" of photosynthesis are also called the

Answer: Calvin cycle Calvin cycle. They don't directly require light, but they need ATP and NADPH from the light reactions.

The oxygen released during photosynthesis comes from

Answer: H₂O (split during the light reactions at PSII) Isotope-labeling experiments confirmed that the oxygen released is from water, not CO₂. Carbon atoms from CO₂ end up in glucose.

AP Biology · Topic 3.5

Photosynthesis Practice

Part of Cellular Energetics.(ENE-1.P)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$The overall equation for photosynthesis is$
- A
  $6 CO₂ + 6 H₂O + light \to C₆H₁₂O₆ + 6 O₂$
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- B
  $ADP + Pi + light \to ATP + H₂O + heat$
- C
  $6 N₂ + 18 H₂ \to 12 NH₃ + 6 light$
- D
  $C₆H₁₂O₆ + 6 O₂ \to 6 CO₂ + 6 H₂O + ATP$
Why
$Carbon fixation + water splitting drives glucose production and oxygen release.$
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Sample 2difficulty 1/5
$The "dark reactions" / "light-independent reactions" of photosynthesis are also called the$
- A
  $Light reactions$
- B
  $Krebs cycle$
- C
  $ETC chain$
- D
  $Calvin cycle$
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Why
$Calvin cycle. They don't directly require light, but they need ATP and NADPH from the light reactions.$
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Sample 3difficulty 1/5
$The oxygen released during photosynthesis comes from$
- A
  $Atmospheric O₂ (recycled in the thylakoid)$
- B
  $Glucose (broken down in stroma releasing O₂)$
- C
  $H₂O (split during the light reactions at PSII)$
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- D
  $CO₂ (split during the Calvin cycle)$
Why
$Isotope-labeling experiments confirmed that the oxygen released is from water, not CO₂. Carbon atoms from CO₂ end up in glucose.$
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Sample 4difficulty 2/5
$The blue thylakoid stacks are the site of$
- A
  $Pyruvate oxidation reactions of cellular respiration$
- B
  $Light-dependent reactions of photosynthesis$
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- C
  $Light-independent reactions of photosynthesis$
- D
  $Oxidative phosphorylation of cellular respiration$
Why
$Thylakoid membranes house PSII, PSI, the cytochrome complex, and ATP synthase — all the light-reaction machinery.$
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Sample 5difficulty 2/5
$A spectrophotometer recorded the absorbance of a chlorophyll a extract across visible wavelengths. The graph below shows the absorption spectrum.$
$Which wavelengths are reflected (not absorbed) by chlorophyll a, giving plants their color?$
- A
  $Around 670 nm (red)$
- B
  $Around 550 nm (green)$
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- C
  $Around 425 nm (blue-violet)$
- D
  $Both 425 and 670 nm$
Why
$Chlorophyll a absorbs strongly in blue (<del> 425) and red (</del> 670) and absorbs least at green wavelengths (~550), which are reflected and reach our eyes.$
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