Photosynthesis Flashcards
What is found in chloroplast ?
- Photosynthetic pigments: chlorophyll a and b, carotenoids
- Photosystem
- Primary electron acceptor
Where are the photosynthetic pigments found ?
Embedded in thylakoid membrane in chloroplast
What feature of chlorophyll allows it to be embedded in the thylakoid membrane ?
- Hydrophobic tail, allowing it to be embedded in the hydrophobic core of the phospholipid bilayer of the thylakoid membrane
- Hydrophilic head allows it to be exposed to the aqueous stroma
What is the function of photosystems ?
Uses light energy form light harvesting antenna to excite electrons to donate to primary electron acceptor
Function of the primary electron acceptor ?
Accepts excited electrons from special pair of chlorophyll a and passes it long the ETC
What is the wavelength that
1. chlorophyll
2. Carotenoids
Absorb
- Red & blue-violet
- Blue-violet
What is the role of
1. Chlorophyll a
2. Cholorphyll b
3. Carotenoid
- Primary pigment that absorbs light energy t initiate LDR
2, 3. Accessory pigment that absorbs light energy and transfers it to chlorophyll a
Where does LDR occur ?
Thylakoids membranes
Outline LDR
- Photoactivation of chlorophyll
- light energy absorbed by photosynthetic pigments in the light harvesting antenna complex and passed from one pigment molecule to another until it reaches the special pair of chlorophyll a in the reaction centre.
- chlorophyll a using light energy to excite electrons and pass it to the primary electron acceptor to be passed to the ETC
- Generation of NADPH and ATP
- electrons pass along EC of progressively lower energy, hence lose energy.
- EC uses energy to pump H+ form the stroma into the thylakoid space, H+ builds up creating PMF
- H+ flows back into stroma via facilitated diffusion through ATP synthase. The movement of H+ allows ADP + Pi converted to ATP via chemiosmosis
- NADP acts has final electron acceptor at end of ETC, accepts H+ to form NADPH
- Photolysis of water
- H2O oxidised split into H+ and O2
- electrons produced replace the electrons that have been excited by the special pair of chlorophyll a
What are the products formed in LDR
NADPH
ATP
O2
How does NADP link LDR and Calvin cycle ?
NADP is the final electron acceptor at the end of ETC, forming NADPH.
NADPH diffuses for thylakoid membrane into the stroma where it is used to convert PGA (3-phosphoglycerate) into TP (triose phosphate) with energy form ATP hydrolysis, concerting NADPH back to NADP. NADP diffuses from stroma back into thylakoid membrane to be used for LDR
Why is light essential in Calvin cycle ?
PGA reduction and regeneration of RuBP requires NADPH and energy form ATP hydrolysis which are produced in LDR.
If there is no light, there is no LDR and no NADPH and ATP for Calvin cycle
Outline the Calvin cycle
- CO2 fixation
- CO2 combines with RuBP to form unstable 6C intermediate catalyst by Rubisco
- 6C intermediate split to form 2 3-phosphoglycerate molecule (PGA)
- PGA reduction
- PGA reduced by NADPH with energy from ATP hydrolysis producing triose phosphate (TP)
- 2 TP combine to form glucose phosphate and used to come other carbohydrates
- Regeneration of RuBP
- TP converts to RuBP using energy form ATP hydrolysis
Identify the features of chloroplast
What is the purpose of compartmentalisation of chloroplast envelope (from cytoplasm) ?
To maintain internal environment optimal for enzymes involved in photosynthesis to fucntion
What is the purpose of compartmentalisation of thylakoid membrane (away from stroma) ?
Allow proton gradient to form to create PMF so that H+ can flow back into stroma for ATP synthesis via chemiosmosis
What is light compensation point ?
Where
rate of photosynthesis = rate of respiration
What is light saturation point ?
Where light intensity stops being limiting any other factors become limiting
Explain how granum is adapted to its fucntion
Stack of thylakoid membranes
Increases SA
- more photosynthetic pigments can embed for more light absorption
- more EC and ATP synthases embedded for more NADPH and ATP synthesis
Impermeable to H+
- H+ build up to create proton motive force for ATP syntheise
What is the relative pH of stroma and thyalokoid during day and night ?
Day: pH of stroma higher than pH of thylakoid
Night: pH of stroma ~ pH of thylakoid
Day VS night: pH of stroma higher in day, pH of thylakoid lower in day
Day photosynthesis occurs, H+ pump into thylakoid space (LDR) less H+ in stroma more H+ in thylakoid
Night photosynthesis stops, no H+ pump into thylakoid from stroma, stroma pH falls, thylakoid pH increases
Define limiting factor
A factor which directly affects the rate of a process when tge magnitude of the factor is changed
How does light affected rate of photosynthesis ?
Limits Calvin cycle as the amount of ATP and NADPH is limited due to slower LDR
How does CO2 conc affect rate of Calvin cycle ?
Increases concentration of substrate for rubisco.
Increase rate of carbon fixation of Calvin cycle
