Photosynthesis Flashcards
Where does the light dependent reaction take place?
In the thylakoids of the chloroplasts
Where does the light independent reaction take place?
Stroma of the chloroplasts
Explain the role of photoionisation
Chlorophyll molecules absorb energy from photons of light
This ‘excites’ 2 electrons causing them to be released from the chlorophyll
Name the two main stages involved in ATP production in the light dependent reaction
Electron transfer chain
Chemiosmosis
What happen in the electron transport chain?
Electrons are released from chlorophyll move down a series of carrier proteins in the thylakoid membrane and undergo a series f redox reactions which releases energy
How is a proton concentration gradient established during chemiosmosis?
Some energy released from the ETC is coupled to the active transport of protons from the stroma into the thylakoid space
How does chemiosmosis produce ATP in the light dependent stage?
Protons move down their concentration gradient from the thylakoid space into the stroma via ATP synthase
Explain the role of light in photolysis
Light energy splits molecules of water
2 H20 = 4H+ + 4e- + O2
What happens to the products of the photolysis of water?
H+ ions: move out of the thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
e-: replace electrons lost from chlorophyll
O2: used to respiration or diffuses out of leaf as waste gas
How and where is reduced NADP produced in the light dependent reaction?
NADP + 2H+ + 2e- = reduced NADP
Catalysed by dehydrogenase enzymes
Stroma of chloroplasts
Where do the H+ ions and electrons used to reduce NADP come from?
H+ ions: photolysis of water
Electrons: NADP acts as the final electron acceptor of the electrons transport chain
Name the 3 stages in the Calvin cycle
- Carbon fixation
- Reduction
- Regeneration
What happens during carbon fixation?
Reaction between CO2 and ribulose bisphosphate catalysed by rubisco
Forms unstable 6C intermediate that breaks down into 2x glycerate 3 phosphate
What happens during reduction?
2x glycerate-3-phosphate are reduced to 2x triose phosphate
Requires 2 x reduced NADP and 2 x ATP
How does the light independent reaction result in the production of useful organic substances?
1C leaves the cycle
What happens during regeneration?
After 1C leaves the cycle the 5C compound Rup forms
RuBP is regenerated from RuP using 1x ATP
Forms 1x ADP
State the roles of ATP and reduced NADP in the light independent reaction
ATP: reduction of glycerate 3 phosphate to triose phosphate and provides a phosphate group to convert RuP into RuBP
Reduced NADP: coenzyme transports electrons needed for reduction of glycerate 3 phosphate to trios phosphate
State the number of carbon atoms in RuBP, glycerate 3 phosphate and triose phosphate
RuBP: 5
Glycerate-3-phosphate: 3
Triose phosphate: 3
Describe the structure of a chloroplast
Disc shaped
Double membrane
Thylakoids: flattened discs stack to form grana
Intergranal lamellae
Stroma
How does the structure of chloroplasts maximise the rate of the light dependent reaction?
ATP synthase channels with granal membrane
Large surface area of thylakoid membrane for ETC
Photosystems position chlorophyll to enable maximum absorption of light
How does the structure of the chloroplasts maximise the rate of the light independent reaction?
Own DNA and ribosomes for synthesis of enzymes
Concentration of enzymes and substrates in stroma is high
What is a limiting factor?
A factor that determines maximum rate of a reaction even if other factors change to become more favourable
Name 4 environmental factors that can limit the rate of photosynthesis
Light intensity
CO2 levels
Temperature
Mineral levels
Outline some agricultural practices used to overcome the effect of limiting factors in photosynthesis
Artificial light
Artificial heating
Addition of CO2 to greenhouse atmosphere
