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Chapter 8 (photosynthesis) - Coggle Diagram
Chapter 8 (photosynthesis)
Molecular features of photosstem
Enhancement Effect
Simultaneous flashes of light at both 680nm and 700nm more than doubles the rate of photosynthesis
Simultaneous flashes of light at both 680nm and 700nm more than doubles the rate of photosynthesis
680nm light strongly activates PSII
700nm light strongly activates PSI
Z scheme
Photosynthesis involves increases and decreases in the energy of an electron as it moves from PSII through PSI to NADPH
Electron on a nonexcited pigment molecule in PSII starts with the lowest energy
Zigzag shape of energy curve
Light excites the electron in PSII
Photosystem I boosts the electron to an even higher energy level
Photosystem II (PSII)
Reaction center
Electron transfers to primary electron acceptor and captured
P680* is relatively unstable, so
energy is transferred quickly
Water is oxidized to replace the electron on P680+, producing oxygen gas in the process
n P680 →P680*
Light-harvesting complex
Directly absorbs photons
Energy transferred via resonance energy transfer
Investigating the redox machine
Photosystem II is an amazing redox machine
Removes high energy electrons from pigment and transfers them to primary electron acceptor
PSII can also remove electrons from water (normally quite stable)
Recent research
biochemical composition of protein complex and role of components
Reactions That Harness Light Energy
Noncyclic and cyclic electron flow
Noncyclic
Electrons begin at PSII and eventually transfer to NADPH, a linear process
Produces both ATP and NADPH in equal amounts
Cyclic photophosphorylation (cyclic electron flow)
Electron cycling releases energy to transport H+ into lumen driving ATP synthesis
Produces only ATP
PSI electrons excited, release energy and eventually return to PSI
Three chemical products
Oxygen, O2: Produced in thylakoid lumen by oxidation of H2O by PSII, Two electrons transferred to P680+ molecules
NADPH: Produced in the stroma from high-energy electrons that start in PSII and are boosted in PSI, NADP+ +2electrons+H+ →NADPH
ATP
Produced in stroma by ATP synthase using the H+ electrochemical gradient
H+ gradient generated three ways: 1) ↑ H+ in thylakoid lumen by splitting of water 2) ↑ H+ by ETC pumping H+ into lumen 3) ↓ H + in stroma from formation of NADPH
ATP synthesis in chloroplasts: Achieved by chemiosmotic mechanism called photophosphorylation……Driven by flow of H+ from thylakoid lumen into stroma via ATP synthase
Photosystems I and II
Captured light energy can be transferred to other molecules to produce energy intermediate molecules for cellular work
PSI
1)Primary role to make NADPH
2)Addition of H+ to NADP+ contributes to H+ gradient by depleting H+ from the stroma
PSII
The initial step in photosynthesis
Excited electrons travel from PSII to PSI
Oxidizes water, generating O2 and H+
Releases energy in electron transport chain (ETC) Energy used to make H+ electrochemical gradient
Absorption vs. action spectrum
Absorption spectrum
that are absorbed by different pigments
Action spectrum
Rate of photosynthesis by whole plant at specific wavelengths
Photosynthetic pigments
Pigments absorb some light energy and reflect others
Leaves are green because they absorb red and violet, and reflect green wavelengths
Absorption boosts electrons to higher energy levels
Having different pigments allows plants to absorb light at many different wavelengths
behaves as particles called photons
Shorter wavelengths have more energy
Travels as waves Short to long wavelengths
Photosynthesis
stages of photosynthesis
Light reactions
Use light energy
Take place in thylakoid membranes
Produce ATP, NADPH and O2
Calvin cycle
Occurs in stroma
Uses ATP and NADPH to incorporate CO2 into carbohydrate
Chloroplast
in plants and algae
Green pigment is chlorophyll
occurs internally in leaves, in the mesophyll
Carbon dioxide enters and oxygen exits leaf through pores called stomata
Chloroplast anatomy
Outer and inner membrane separated by intermembrane space
A third membrane, the thylakoid membrane contains pigment molecules
Granum stack of thylakoids
Membrane forms thylakoids Enclose thylakoid lumen
Tropic levels
Heterotroph Autotroph Photoautotroph
Must eat food (organic molecules from their environment) to sustain life
Makes organic molecules from inorganic sources
Use light as a source of energy Green plants, algae, cyanobacteria
Energy cycle
cells use organic molecules for energy and plants replenish those molecules using photosynthesis
In the process plants also produce oxygen
Variations in Photosynthesis
CAM plants
C4 plants separate processes using time
Crassulacean Acid Metabolism
open their stomata at night
CO2 enters and is converted to malate
Stomata close during the day to conserve water
Oxaloacetate converted to malate
Malate broken down into CO2 to drive Calvin cycle during the day
C4 plants
1)minimize respiration 2)Hatch-Slack pathway
3)Leaves have two-cell layer organization
Photorespiration
Rubisco functions as a carboxylase
Rubisco can also be an oxygenase
in hot and dry environments
Favored when CO2 low and O2 high
Environmental conditions can influence both the efficiency and way the Calvin cycle works
Synthesizing Carbohydrates via the Calvin Cycle
Phases
1)Carbon fixation 2)reduction and carbohydrate production3)regeneration of RUBP