Photosynthesis Flashcards
Carbon fixation?
- Process by which inorganic carbon (CO2) is converted into an organic molecule
- Excited electrons from photolysis power this process
Photosynthesis Reactants
6 CO2
6 H2O
Photosynthesis Products
1 Glucose
6 O2
Photosynthesis process features
Non-spontaneous
Endergonic (anabolic)
Produces glucose
Cellular Respiration features
Spontaneous
Exergonic (catabolic)
Breaks down glucose
Leaf Anatomy:
Epidermis
Outer layer of cells
Provides protection & prevents water loss
Leaf Anatomy:
Palisade mesophyll cells
Right below upper epidermis
Many chloroplasts
Most photosynthesis occurs here
Leaf Anatomy:
Spongy mesophyll cells
Bottom of leaf
Gas exchange occurs here
Some chloroplasts for mid amounts of photosynthesis
Leaf Anatomy:
Stomata
Pores on underside of leaf where gas can enter & exit.
Leaf Anatomy:
Guard cells
Surround stomata & control their opening/closing.
Leaf Anatomy:
Chloroplasts
Found in plants & photosynthetic algae
NOT in cyanobacteria
Similar to mitochondria & Contain these structures (outermost to innermost):
- Outer mem
- Inter mem
- Inner mem
- Stroma
- Thylakoids
- Thylakoid lumen
Leaf Anatomy:
Stroma
Fluid inside the inner membrane
Calvin cycle occurs here!!
Leaf Anatomy:
Thylakoids
Within the stroma
Light dependent reactions occur here!!!
Individual membrane= are thylakoids
Stack=granum
Leaf Anatomy:
Thylakoid lumen
Interior of the thylakoid & H+ ions accumulate here, making it acidic
Light dependent reactions produce what
ATP and NADPH
What kind of special pigments absorb photons?
Chlorophyll and carotenoids
What is the reaction center?
A special pair of chlorophyll molecules in the center
What kind of ring structure does chlorophyll have?
A porphyrin ring structure w/ a magnesium atom bound in its center
What photosystems are involved in photosynthesis?
Photosystem II (P680) and Photosystem I (P700) are used in photosynthesis.
__________ is carried out by the light-dependent reactions.
Non-cyclic photophosphorylation
Non-cyclic photophosphorylation steps
- Photolysis (electrons sent to PS2 & protons into thylakoid lumen
- Excited electrons in PS2, electrons passed to primary electron acceptor
- Electrons sent to ETC, protons from stroma to thylakoid lumen, electrons to PS1
- Photons excite pigments in PS1
- NADP+ reductase reduces NADP+ into NADPH
- Electrochemical gradient created, ATP produced (ATP synthase)
What is cyclic photophosphorylation and its specific features?
- PSI passes electrons back to 1st ETC instead of the 2nd ETC
- More proton pumping & ATP production
- NO NADPH is generated.
What is the Calvin cycle
Light-independent reactions
- DO NOT directly use light energy
- Can only occur if the light-dependent rxns provide ATP & NADPH
Where does the calvin cycle take place
- Chloroplast stroma of plant mesophyll cells
- Fixes carbon dioxide that enters stomata
Calvin Cycle Steps
- Carbon fixation
- Reduction
- Regeneration
- Carbohydrate Synthesis
Carbon fixation
- Forms 6-carbon molecules, which quickly break down into 3-carbon phosphoglycerates (PGA)
- Catalyzed by RuBisCo.
Reduction
PGA is phosphorylated by ATP & reduced by NADPH to form G3P
Regeneration
G3P is converted back to RuBP.
Carbohydrate synthesis
G3P is used to make glucose.
What is photorespiration
Produces phosphoglycolate
Oxygen binds to RuBP
NO new glucose made
Net loss of fixed carbon atoms
Also called C2 photosynthesis
Where does photorespiration occur?
Stroma
In photorespiration, where is the phosphoglycolate shuttled to? What is it converted into?
Peroxisomes and mitochondria
Conversion into PGA.
Why are stomata closed?
What accumulates in the leaf? What binds to Oxygen?
- To minimize water loss
- Oxygen accumulates inside the leaf while carbon dioxide is used up
- RuBisCo binds oxygen and photorespiration occurs.
C3 photosynthesis
Normal photosynthesis, where 3-carbon PGA is produced.
What does C4 photosynthesis produce and where does it occur?
- Produces 4-carbon oxaloacetate
- Occurs in plants living in hot environments
In C4 photosynthesis, CO2 is first converted into ________ and this intermediate is produced in _____
oxaloacetate, mesophyll cell
C4 photosynthesis steps
- PEP carboxylase fixes CO2 into PEP molecule, produces oxaloacetate then converted to malate in the mesophyll cell.
- Malate transferred to bundle sheath cells (lower O2)
- Malate decarboxylated to release CO2, spatially isolating where CO2 is fixed by RuBisCo
- Pyruvate converted back into PEP
What type of photosynthesis do plants found in hot, dry climates use? Why?
C4
To limit photorespiration, a wasteful process whereby RuBisCo binds oxygen to ribulose-1,5-bisphosphate (RuBP) instead of carbon dioxide (CO2).
C4 photosynthesis _____ isolates the Calvin cycle to bundle sheath cells to limit ______ since these cells are relatively impermeable to gases, including oxygen.
spatially, photorespiration
What is the drawback to having spatially isolated where CO2 is fixed by RuBisCo?
Pyruvate is also produced & needs to be shuttled back to mesophyll cells using ATP
Crassulacean acid metabolism (CAM) photosynthesis
Uses temporal isolation of carbon dioxide to prevent photorespiration in hot environments
CAM photosynthesis steps
- DAY: stomata are closed to prevent transpiration (evaporation of water from plants)
- NIGHT: stomata are open so CO2 comes in
- PEP carboxylase fixes CO2 into PEP, producing oxaloacetate and afterwards malate
- Malate is stored in vacuoles instead of being shuttled to bundle sheath cells
- NEXT DAY: the stomata are closed again, malate converted back to oxaloacetate, which releases CO2 and PEP
- CO2 accumulates in the leaf for use in the Calvin cycle through temporal isolation
Products of non-cyclic photophosphorylation
O2, ATP and NADH
