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Photosynthesis
Ecological Significance
Ecological Significance Photosynthesis- the process that converts light
energy to chemical energy
Autotrophs- “self + feeders”
Photoautotrophs- “light + self + feeders”
Heterotrophs- “ other + feeders”
Consumers- eat other things
Decomposers- break down dead organic material
Chloroplast Structure Leaf Structure
The leaf is the major site of photosynthesis
Stomata- small pores in the leaf where CO2 enters an O2 and H2O leave
Mesophyll Tissue in center of the leaf Where chloroplasts are found
Chloroplast Structure Double Membrane
Stroma- fluid inside the inner membrane but outside the thylakoid
Thylakoid interconnected membranous sacks
Granna (granum)- stacks of thylakoids
Thylakoid Space- the space inside the thylakoid
Chlorophyll- green pigment found inside (embedded in) the thylakoid membrane
Chemical Context of Photosynthesis General Equation
6CO2 + 6H2O + light energy → C6H12O6 + 6O2
Redox Reaction
Reverse of cellular respiration
Electrons increase in potential energy as they move from water to sugar
Anabolic reaction- builds up large organic molecules from smaller ones
Requires energy that is supplied by the sun
Light and Pigments Pigments- molecules that absorb light
Visible Light- 750nm-380nm (ROYGBIV)
Absorbance vs. Transmittance/Reflection Absorbance- wavelengths that are absorbed
(colors that you don’t see)
Transmittance- wavelengths that bounce off or go through a substance (colors that you do see)
Plant Pigments Chlorophyll a- reflects blue-green wavelengths
(all others are captured)
Chlorophyll b- reflects yellow-green wavelengths (all others are captured)
Carotenoids- reflects yellow and orange wavelengths
Major function of carotenoids= photoprotection- absorbs excessive light energy that could otherwise be harmful
The Big Picture of Photosynthesis
Light Reactions “photo” = light
Also known as: Light Dependent Reactions
Location: thylakoid membrane (photosystems I & II and the electron transport chain)
Input: light (photons) + H2O + NADP+ + ADP + P
Output: O2 + NADPH + ATP
Reaction: light + H2O → O2
Calvin Cycle “synthesis”= make, put together
Also known as: Light Independent Reactions, Dark Reactions
Location: stroma
Input: NADPH + ATP + CO2
Output: G3P (later converted to glucose) + NADP+ + ADP + P
Reaction: CO2 → C6H12O6
The Light Reaction Photosystems- a protein complex embedded
in the thylakoid membrane that contains two parts:
Reaction Center- protein complex that holds a special chlorophyll a molecule and a primary electron acceptor
Light-harvesting complex- pigment molecules that capture light and transfer excited electrons to the special chlorophyll a molecues
Two Kinds of Photosystems Photosystem II:
Special chlorophyll a= P680 Functions 1st
Photosystem I: Special chlorophyll a= P700 Functions 2nd
P680 and P700 Very unstable when oxidized so electrons
must be replenished immediately
P700 is replenished with electrons moving down the ETC from P680
P680 is replenished by the splitting of water molecules
Noncyclic Electron Flow
Cyclic Electron Flow the calvin cycle uses more ATP than NADPH
a build up of NADPH triggers the switch from noncyclic to cyclic electron flow
Uses only PSI
Electrons cycle back from Ferredoxin (Fd) to the cytochrome complex to replenish P700
Does not produce NADPH or O2 but does produce ATP
Chemiosmosis in the Chloroplast Energy from sunlight, not food
Build up of H+ occurs in the thylakoid space
Enzyme: ATP synthase
Overall Result of the Light Reactions: solar power generates ATP and NADPH providing chemical energy and reducing power to the Calvin cycle
Overall Result of the Light Reaction Solar power generates ATP and NADPH
providing chemical energy and reducing power to the Calvin cycle
The Clavin Cycle Input: 3 CO2 (one at a time) + 9 ATP +
6NADPH
Output: glucose
Three Major Steps of the Calvin Cycle Carbon Fixation- carbon is incorporated into
organic forms from carbon dioxide
CO2 is converted into carbohydrates using the energy provided by ATP and NADPH from the light reactions
Back to the Big Picture of Photosynthesis