Photosynthesis

Photosynthesis consists of two processes
– The light reactions
 Occur in the grana
 Split water, release oxygen, produce ATP, and form NADPH

– The Calvin cycle
 Occurs in the stroma
 Forms sugar from carbon dioxide, using ATP for energy and NADPH for reducing power


• Overview: The Process That Feeds the Biosphere
• Photosynthesis
– Is the process that converts solar energy into chemical energy

• The leaves of plants
– Are the major sites of photosynthesis

• Photosynthesis is summarized as

6 CO2 + 12 H2O + Light energy ® C6H12O6 + 6 O2 + 6 H2 O

• Chloroplasts
– Are the organelles in which photosynthesis occurs
– Contain thylakoids and grana

• Photosynthesis consists of two processes
– The light reactions
 Occur in the grana
 Split water, release oxygen, produce ATP, and form NADPH

– The Calvin cycle
 Occurs in the stroma
 Forms sugar from carbon dioxide, using ATP for energy and NADPH for reducing power
• Pigments
– Are substances that absorb visible light
- Chlorophyll a
Is the main photosynthetic pigment
- Chlorophyll b
Is an accessory pigment


• An overview of photosynthesis

Produces NADPH, ATP, and oxygen

• The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
• The Calvin cycle
– Is similar to the citric acid cycle
– Occurs in the stroma
• The Calvin cycle has three phases
– Carbon fixation
– Reduction
– Regeneration of the CO2 acceptor

The Calvin cycle

• Chloroplasts and mitochondria
– Generate ATP by the same basic mechanism: chemiosmosis
– But use different sources of energy to accomplish this

Differs in chloroplasts and mitochondria

• In both organelles
– Redox reactions of electron transport chains generate a H+ gradient across a membrane
• ATP synthase
– Uses this proton-motive force to make ATP