Stages of Photosynthesis
Stage 1 ‐‐ Energy is captured from sun.
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Leaves contain light absorbing substances called pigments
Pigments absorb certain wavelengths of light and reflect others
Chlorophyll: the primary pigment involved in photosynthesis
Absorbs blue & red light
Reflects green & yellow light (causes plants to look green)
2 types of chlorophyll:
Chlorophyll a (bright green)
Chlorophyll b (yellow‐green)
Carotenoids: pigments that produce red, orange, & yellow colors (fall leaves, fruits, flowers,
etc.)
Clusters of pigments are embedded inside the chloroplasts (specifically, in the thylakoids)
Light strikes the thylakoids inside the chloroplasts & energy is transferred to the chlorophyll.
Water molecules are split to form oxygen gas (O2).
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Stage 2 ‐‐ Light energy is converted to chemical energy.
 Excited electrons jump to nearby molecules in the thylakoid membrane
 Then the electron is passed down a series of molecules along the thylakoid membrane (electron
transport chain)
 Electron transport chains provide the energy needed to make ATP
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Stage 3 ‐‐ Energy is stored in organic compounds (sugars).
 Carbon dioxide fixation: the transfer of CO2 from atmosphere to organic compounds
 Calvin cycle: a series of enzyme‐assisted chemical reactions that produces a 3‐carbon sugar
(uses energy from ATP)
 3 CO2 molecules enter the cycle & produce a 3‐carbon sugar
 These sugars provide organisms energy to maintain life