5.1 Photosynthesis Flashcards
Where does the light dependent reaction occur in plants?
Thylakoids of the chloroplasts
Where does the light independent reaction occur in plants?
Stroma of the chloroplasts
Explain the role of light of photoionisation.
Chlorophyll molecules absorb energy from photons of light
This raises 2 electrons to a higher energy level to release them from the chlorophyll
Name the 2 main stages involved in ATP production in the LDR.
- Electron Transfer Chain (ETC)
- Chemiosmosis
What happens in the ETC?
Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane
Undergo a series of redox reactions to release energy
How is a proton concentration gradient established during chemiosmosis?
Some energy released from ETC is coupled to the active transport of H+ ions from stroma into thylakoid space
How does chemiosmosis produce ATP in the light dependent stage?
H+ ions move down their concentration gradient from thylakoid space into stroma via the channel protein ATP synthase
What does ATP synthase catalyse?
ADP + Pi -> ATP
Explain the role of light in photolysis.
Splits molecules of water
Give the equation for the photolysis of water.
2H₂O -> 4H⁺ + 4e⁻ + O₂
What happens to the H⁺ produced in the photolysis of water?
Move out of thylakoid space via ATP synthase
Used to redyce the coenzyme ATP
What happens to the e⁻ produced in the photolysis of water?
Replace electrons lost from chlorophyll
What happens to the O₂ produced in the photolysis of water?
Used for respiration or diffuses out of leaf as waste gas
Where is reduced NADP produced in the LDR?
Stroma of chloroplasts
How is reduced NADP produced in the LDR?
NADP + 2H⁺ + 2e⁻ -> reduced NADP
Catalysed by dehydrogenase
Where do H⁺ ions used to reduce NADP come from?
Photolysis of water
Where do electrons used to reduce NADP come from?
NADP acts as the final electron acceptor of the ETC
Name the 3 stages of the Calvin Cycle.
Carbon fixation
Reduction
Regeneration
What happens during carbon fixation in the Calvin cycle?
Reaction between CO₂ & RuBP catalysed by rubisco
Forms unstable 6C intermediate that breaks down into 2GP
What is meant by RuBP?
Ribulose BisPhosphate
What is meant by GP?
Glycerate 3-Phosphate
What happens during reduction in the Calvin cycle?
2GP are reduced to 2TP
Requires 2NADP & 2ATP
Forms 2NADP & 2ADP
What is meant by TP?
Triose Phosphate
How does the LIR result in the production of useful organic substances?
1C leaves the cycle
What happens during regeneration in the Calvin cycle?
1C leaves the cycle
5C compound RuP forms
RuBP is regenerated from RuP using 1ATP
Forms 1ADP
State the role of ATP in the LIR.
Reduction of GP to TP
Provides phosphate group to convert RuP into RuBP
State the role of reduced NADP in the LIR.
Coenzyme transports electrons needed for reduction of GP to TP
What number of carbon atoms does RuBP have?
5
What number of carbon atoms does GP have?
3
What number of carbon atoms does TP have?
3
Describe the structure of a chloroplast.
Disc-shaped
Double membrane
Thylakoids
Intergranal lamellae
Stroma
What are the thylakoids of a chloroplast?
Flattened discs stack to form grana
What are the intergranal lamellae of a chloroplast?
Tubular extensions attach thylakoids in adjacent grana
What is the stroma of a chloroplast?
Fluid-filled matrix
How does the structure of a chloroplast maximase the rate of the LDR?
ATP synthase channels within granal membrane
Large SA of thylakoid membrane for ETC
Photosystems position chlorophyll to enable maximum absorption of light
How does the structure of a chloroplast maximase the rate of the LIR?
Own DNA & ribosomes for synthesis of enzymes e.g. rubisco
Concentration of enzymes & substrates in stroma is high
Define limiting factor.
Factor that determines maximum rate of a reaction, even if other factors change to become more favourable
Name 4 environmental factors that limit the rate of photosynthesis.
Light intensity
CO₂ levels
Temperature
Mineral/magnesium levels
What part of photosynthesis does light intensity affect?
Light dependent stage
What part of photosynthesis do CO₂ levels affect?
Light dependent stage
What part of photosynthesis does temperature affect?
Enzyme controlled steps
What part of photosynthesis do mineral levels affect?
Normal functioning of chlorophyll
Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis.
Artificial light
Artificial heating
Addition of CO₂ to greenhouse atmosphere
Why do farmers try to overcome the effect of limiting factors?
Increase yield
Additional cost balanced with yield to ensure maximum profit
State the purpose and principle of paper chromatography.
Molecules in a mixture are separated based on their relative attraction to the mobile phase vs stationary phase
Outline a method for extracting photosynthetic pigments.
Using a pestle and mortar to grind a leaf with an extraction solvent
Outline how paper chromatography can be used to separate photosynthetic pigments.
Use capillary tube to spot pigment extract onto pencil origin
Place chromatography paper in solvent with origin above solvent level
Allow solvent to run until almost at other end of paper
Pigments move different distances
Where does the origin line go?
1cm above bottom of paper
Why is origin line drawn in pencil?
Pencil isn’t soluble
What are Rf values?
Ratios that allow comparison of how far molecules have moved in chromatograms
How are Rf values calculated?
Distance to origin/distance to solvent front
