🌿 Chapter 10: Photosynthesis—The Life-Giving Process
Photosynthesis is the process that converts light energy into chemical energy (sugar), performed by
plants, algae, and some bacteria (photoautotrophs).
6CO2 + 12H2 O + Light Energy → C6 H12 O6 + 6O2 + 6H2 O
1. Photosynthesis Overview: The Two Stages
Photosynthesis occurs in the chloroplast and is divided into two interdependent stages:
Stage Location Inputs Outputs Purpose
Light Thylakoid Membranes H2 O, ADP,
ATP, NADPH, Convert light energy into
Reac NADP+ , Light O2 chemical energy (ATP
tions and NADPH).
Calvi Stroma CO2 , ATP,
Sugar (G3P), Use the energy to fix
n NADPH ADP, NADP+ CO2 into organic sugar
Cycle molecules.
2. The Light Reactions: Capturing Energy
The light reactions use two main Photosystems (I and II), both containing light-harvesting pigment
complexes.
A. Key Components
Pigments: Molecules that absorb specific wavelengths of light.
Chlorophyll a: The primary pigment, participates directly in light reactions (absorbs blue-
violet and red).
Chlorophyll b: An accessory pigment (absorbs blue and orange).
Carotenoids: Yellow/orange accessory pigments; also provide photoprotection (dissipate
excess light energy that could damage chlorophyll).
Photosystems (PS): Complexes of pigments and proteins embedded in the
thylakoid membrane.
PS II (P680): Functions first; splits water.
PS I (P700): Functions second; reduces NADP+ .
B. The Process (Linear Electron Flow)
1. Water Splitting: Light strikes PS II (P680), exciting electrons. Water (H2 O) is split to replace the
lost electrons, releasing O2 as a byproduct.
2. Electron Transport Chain (ETC): Excited electrons travel from PS II to PS I. This movement
pumps H+ ions into the thylakoid space.
3. Chemiosmosis (Photophosphorylation): The resulting H+ gradient powers ATP
Photosynthesis is the process that converts light energy into chemical energy (sugar), performed by
plants, algae, and some bacteria (photoautotrophs).
6CO2 + 12H2 O + Light Energy → C6 H12 O6 + 6O2 + 6H2 O
1. Photosynthesis Overview: The Two Stages
Photosynthesis occurs in the chloroplast and is divided into two interdependent stages:
Stage Location Inputs Outputs Purpose
Light Thylakoid Membranes H2 O, ADP,
ATP, NADPH, Convert light energy into
Reac NADP+ , Light O2 chemical energy (ATP
tions and NADPH).
Calvi Stroma CO2 , ATP,
Sugar (G3P), Use the energy to fix
n NADPH ADP, NADP+ CO2 into organic sugar
Cycle molecules.
2. The Light Reactions: Capturing Energy
The light reactions use two main Photosystems (I and II), both containing light-harvesting pigment
complexes.
A. Key Components
Pigments: Molecules that absorb specific wavelengths of light.
Chlorophyll a: The primary pigment, participates directly in light reactions (absorbs blue-
violet and red).
Chlorophyll b: An accessory pigment (absorbs blue and orange).
Carotenoids: Yellow/orange accessory pigments; also provide photoprotection (dissipate
excess light energy that could damage chlorophyll).
Photosystems (PS): Complexes of pigments and proteins embedded in the
thylakoid membrane.
PS II (P680): Functions first; splits water.
PS I (P700): Functions second; reduces NADP+ .
B. The Process (Linear Electron Flow)
1. Water Splitting: Light strikes PS II (P680), exciting electrons. Water (H2 O) is split to replace the
lost electrons, releasing O2 as a byproduct.
2. Electron Transport Chain (ETC): Excited electrons travel from PS II to PS I. This movement
pumps H+ ions into the thylakoid space.
3. Chemiosmosis (Photophosphorylation): The resulting H+ gradient powers ATP
