Photosynthesis
Concepts of Photosynthesis
Cells are highly order
Entropy is when cells become disordered
Entropy cannot be prevented
Sunlight maintains and increases order
Directly
Indirectly
Through photosynthesis
Through respiration
Two types of organisms
Photoautotrophs
Heterotrophs
gather energy from light
gather energy from organic materials
Tissues and organs
Can be photoautotrophic
Chlorophyllous leaves and stems
Can be heterotrophic
Roots, wood, and flowers
Tissues can change metabolism
Seedlings are heterotrophs during germination
Become photoautotrophic when exposed to sunlight
Immature fruits photosynthesize
During maturation, chloroplasts convert to chromoplasts
Energy and Reducing Power
Energy Carriers
Sunlight is captured by pigments
ATP is an essential molecule
Energized pigments enter into two reactions
Despite thousands of different reactions
Two theories of transport
Allow pigments into necessary reactions
Allow pigments to be less energized
Problem: Pigments are large and not mobile
ATP is produced for for energy
Guanosine triphosphate is also made
However, it's a small fraction of plant bodies
It is recycled and reused
There are 3 ways ATP is produced
Photophosphorylation
Substrate level phosphorylation
Oxidative phosphorylation
Involves light energy
Occurs in the last stage of respiration
When compounds give their phosphate away
Reducing power
Oxidation is where an atom has less electrons (e-)
Reduction is when e- are gained
Oxidative compounds often have oxygen
Reduced compounds contain hydrogen
Reducing power is the ability to force e- onto a compound
Especially important in plants
NAD+ and NADP+ move e-
They are oxidizing agents
NADH and NADPH are formed
Reducing agents
Has redox potential
The ability to accept and donate e-
Other e- carriers
Cytochromes
Small proteins that contain iron atom
Moves e- short distances
Plastoquinones
Also carry e- short distances
Plastocyanin
Contains copper atom
Carries small distances
Photosynthesis
Light-dependent reactions
Light is part of the Electromagnetic radiation spectrum
Most materials absorb certain wavelengths
These are called pigments
Photosynthetic pigments captures light energy
Chlorophyll a captures red and blue light
Causes an e- to be activated
Goes from a grounded state to an excited state
The release of light is called fluorescence
Absorption spectrum
Shows which wavelength is most absorbed
Action spectrum
Shows which wavelength is most effective
Accessory pigments
Other pigments that absorb light
They form an antenna complex
Energy is transferred to the reaction center
All pigments are carriers are in a photosynthetic unit
Photosystem I
Reaction center P700
The e- is then passed to Fx
Fx reduces the e- and passes it to ferredoxin
Then passed to ferredoxin-NADP+ reductdase
NADPH is formed
Photosystem II
Reaction center P680
Then goes to the plastoquinone
Gives e- to cytochrome b6f
Then donated to a plastocyanin to give to PSI
ATP synthesis
chemiosmotic phosphorylation
Hydrogen ions are pumped from stroma into lumen
Hydrogen ions are then diffused through the ATP synthase
Noncylic electron transport
When e- flow smoothly from water
Cylic electron transport
E- go back through the photosystems to get more energy
Stroma reactions
Also known as the Calvin cycle
An acceptor molecule reacts with CO2
2 3-phosphoglycerates are formed
RUBISCO is the enzyme that carries out this cycle
3-phosphoglycerates are converted to 1,3-diphoshpoglycerates
Then reduced to 3-phoshpoglyceraldehyde
Anabolic Metabolism
Used to store energy
Short-term
Intermediate-term
Long-term
ATP and NADPH
Glucose and Sucrose
Starch and lipids
Polysaccharide synthesis
Glucose is made by gluconeogenesis
PGAL is converted to dihydroxyacetone
Then fructose-1,6-biphosphate
Loses a phosphate to become fructose-6-phosphate
Rearranged into glucose-6-phosphate
Made into glucose
Starch is made from many glucose molecules bonding together
Environmental and Internal Factors
Light
Quality
Depends on the different colors of light coming to
Quantity
The intensity of the light
Duration
Number of hours of light available
Leaf Structure
Controls how much sunlight, water, and CO2 can be used
Water
Water is essential, so plants can store water for needed use
C4 metabolism
Used to improve condition for RUBISCO
This will increase stromal reaction rates
Crassulacean Acid Metabolism
Another process that helps conserve water while still doing photosynthesis
Not particularly effective, but can be useful for hot and dry areas