Photosynthesis Flashcards
Where does the light-dependent reaction occur in plants?
In the thylakoids of chloroplasts
Where does the light-independent reactions occur in plants?
In the stroma of chloroplasts
Explain the role of light in photoionisation
- chlorophyll molecules absor energy from photons of light
- excites 2 electrons causing them to be released from the chlorophyll
What does exciting an electron mean?
Raising it to a higher energy level
What are the 2 main stages involved in ATP production in the light-dependent reaction?
- ETC
- chemiosmosis
What happens in the ETC?
Electrons released from chlorophyll moved down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reaction, 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 H+ ions 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 back into the stroma via the channel protein ATP synthase
Explain the role of light in photolysis
Light energy splits molecules of water
What are the products of photolysis of water?
- H+ ions
- e-
- O2
What happens to H+ ions in photolysis?
Move out of thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
What happens to electrons in photolysis?
Replace electrons lost from chlorophyll
What happens to oxygen in photolysis?
Used for 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 ETC
Name the 3 main stages in the Calvin cycle
- carbon fixation
- reduction
- regeneration
What happens during carbon fixation?
- Reaction between CO2 & RuBP catalysed by rubisco
- Forms unstable 6C intermediate that breaks down into 2x GP
What happens during reduction in the Calvin cycle?
- 2x GP are reduced to 2x TP
- requires 2x reduced NADP & 2x ATP
- forms 2x NADP & 2x ADP
How does the light-independent reaction result in the production of useful organic substances?
1C leaves the cycles
- some of the TP is converted into useful organic molecules
What happens during regeneration in the Calvin cycle?
- after 1C leaves the cycle, the 5C compound RuP forms
- RuBP is regenerated from RuP using an ATP
- forms 1 ADP
State the roles of ATP & reduced NADP in the light-independent reaction
- ATP: reduction of GP to TP & provides phosphate group to convert RuP into RuBP
- reduced NADP: coenzyme transports electrons needed for reduction of GP to TP
How many carbon atoms in RuBP, GP & TP?
RuBP: 5
GP: 3
TP:3
Describe the structure of a chloroplast
- usually disc-shaped
- double membrane
- thylakoids
- integranal lamellae
- stroma
What is a thylakoid?
Flattened disc that stacks to form grana
