5.6 PHOTOSYNTHESIS Flashcards
Structure of the chloroplast
What are thylakoids in the chloroplast?
- Folded membranes which contain photosynthetic pigment (chlorophyll) and photosystems
What is stroma in the chloroplast?
- fluid centre of the chloroplast with RUBISCO enzymes
What is the grana in the chloroplast?
- stacks of thylakoids
What is the outer membrane of a chloroplast?
- Highly permeable membrane that controls the entry/exit in chloroplast
What is a photosystem and where are they located?
- Photosystems are a bunch of photosynthetic pigments found in the thylakoids
What is meant by a photosynthetic pigment?
- Different pigments that absorb specific wavelengths of light
What are *accessory pigments**, where are they based in photosystems and what do they do?
- Chlorophyll B/ Carotenoids
- Light harvesting system
- Light energy absorbed is passed to the reaction centres
Where is the *primary pigment**, where is it based in photosystems and what does it do?
- Chlorophyll A
- Reaction centres
- Where light dependant stage happens
State the Rf value equation
Where does the light-dependant stage occur?
- Thylakoids
What reactions does the light-dependant stage consist of? (4)
1) Non-cyclic photophosphporilation
2) Cyclic photophosphporilation
3) Photolysis
4) Chemiosmosis
What two things are produced by the light-dependant stage?
- ATP
- Reduced NADP/NADPH
Name the two photosystems used in the light-dependant stage.
- PSII (used first) and PSI (used after)
Describe non-cyclic photophosphporilation
- Light energy absorbed by photosynthetic pigments causes electrons in the reaction centre chlorophyll of PSII to become excited & released to electron carriers
- Electron carriers combine with electron (to become reduced to Fe2+ then donates the electron to next electron carrier to become re-oxidised to Fe3+) which moves excited electrons along the electron transport system to PSI
- The movement of electrons through the electron transport chain results in ATP production at the end via chemiosmosis
- Electrons lost from the reaction centre chlorophyll of PSII are replaced by electrons from photolysis and electrons lost from reaction centre chlorophyll of PSI are replaced by electrons from PSII
- At PSI reaction centre the electrons are released and accepted by the coenzyme NADP along with H+ protons from photolysis to produce reduced NAPD (NADPH)
Describe cyclic photophosphporilation
- Some electrons released from the reaction centres of PSI are not picked up by the coenzyme NADP and are instead recyled back into PSI
- The movement of electrons along the electron transport chain still results in ATP production by chemiosmosis
- However reduced NADP (NADPH) is not produced
Describe photolysis
- Light energy absorbed by chlorophyll in PSII is used (along with an enzyme) to split water into oxygen, H+ and e-
- The H+ proton is picked up by NADP to produce reduced NADP (NADPH)
- The electron from this replaces the electrons lost from the reaction centre chlorophyll of PSII
- The oxygen is used for respiration or diffuses out the leaf
Describe chemiosmosis
- When excited electrons move along the electron transport chain through the embedded electron carriers in thylakoid membrane energy is released
- Some of this energy is used to pump H+ protons from photolysis across the thylakoid membrane from the stroma to the thylakoid space
- This creates an electrochemical gradient as many H+ protons are now in the thylakoid space
- As a result, H+ protons diffuse down the electrochemical gradient, back across the thylakoid membrane through the enzyme ATP synthase
- When H+ protons pass through, ATP synthase converts ADP + Pi into ATP
- The H+ protons now combine with the coenzyme NADP to form reduced NAPD (NAPH)
Describe the three roles of water in photosynthesis
1) Source of H+ protons for photophosphorilation (NADPH production)
2) Replaces electrons lost from reaction centre chlorophyll of PSII
3) Keeps plant turgid
Where does the light-independant stage occur?
- Stroma
What does the light-independant stage consist of?
- The calvin cycle
Draw and describe the calvin cycle
What is produced in the light-independant stage?
- Hexose sugar
State the uses of TP during the calvin cycle
- Can form the disaccarise sucrose
- Can form the polysaccarides starch or cellulose
- Can form amino acids
- Can form lipids
- Can regenerate RuBP for calvin cycle
The three limiting factors of photosynthesis?
How does decreasing light intensity affect levels of GP, TP and RuBP?
- Lower light intensity reduces GP, TP and RuBP because ATP and NADPH is reduced during the light dependent stage
How does **decreasing carbon dioxide* affect levels of GP, TP and RuBP?
- Lower carbon dioxide increases RuBP but reduces GP, TP because RuBP accumulates as it cannot react with low levels of carbon dioxide meaning GP and TP cannot be produced.
How does **increasing temperature* affect levels of GP, TP and RuBP?
- Higher temperature increases GP, TP and RuBP as more kinetic energy means more successful collisions until temperature is too high, RuBP denatures
