Photosynthesis
Photosynthetic autotrophs

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Plants, some bacteria and protists
Autotrophs generate their own organic matter through photosynthesis
Sunlight energy is transformed to energy stored in the form of chemical bonds
Why are plants green?
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Chloroplasts (organelle) full of chlorophyll (organic molecule)
Chloroplasts absorb sunlight (light energy) and convert it to sugar (chemical
energy)
Photosynthesis

Process by which autotrophic organisms use light energy to make sugar and
oxygen gas from carbon dioxide and water
Plants:
photosynthesis occurs primarily in the chloroplasts
Algae & Cyanobacteria
also contain chloroplasts
A chloroplast contains:
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Stroma = a fluid
Grana = stacks of thylakoids
Thylakoids = contain chlorophyll
o Chlorophyll is the green pigment that captures light for photosynthesis
Other pigments (go through photsynthesis)
Plastids contain several pigments
All can conduct photosynthesis
Different pigments absorb light at different wavelengths
 Chlorophyll a
 Chlorophyll b
 Cartenoids
 Xanthophyll
Chemical Reaction
(LIGHT)
6CO2 + 6H2O C6H12O6 + 6O2
Steps of Photosynthesis: Part 1 light reaction
1.
2.
3.
4.
5.
Light (from sun) hits chlorophyll (found in chloroplasts)
Plant takes in Carbon dioxide from (leaves) and water from roots
Chlorophyll vibrates and causes water to break apart.
Oxygen is released into air.
Hydrogen remains in chloroplast attached to NADPH

Electron transport chains generate ATP, NADPH, & O

o Two connected photosystems collect photons of light and transfer the
energy to chlorophyll electrons
o The excited electrons are passed from the primary electron acceptor to
electron transport chains
Energy ends up in ATP and NADPH
2
Photosynthesis Part 2: Calvin Cycle (light independent reaction)
1. CO from atmosphere is joined to H from water molecules (NADPH) to form
2
glucose
2. Glucose can be converted into complex molecules (disaccharides =
carbohydrates)
3. The electron transport chains are arranged with the photosystems in the
+
thylakoid membranes and pump H through that membrane
+
a. The flow of H back through the membrane is harnessed by ATP synthase
to make ATP
+
+
b. In the stroma, the H ions combine with NADP to form NADPH
Calvin Cycle (light independent reactions)
1. Carbon from CO2 is converted to glucose
2. ATP and NADPH drive the reduction of CO2 to C H O
6
12
6
Calvin Cycle
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•
•
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CO2 is added to the 5-C sugar RuBP by the enzyme rubisco.
This unstable 6-C compound splits to two molecules of PGA or 3phosphoglyceric acid.
PGA is converted to Glyceraldehyde 3-phosphate (G3P), two of which bond to
form glucose.
G3P is the 3-C sugar formed by three turns of the cycle.