8.3 Photosynthesis

Question 1

Where do light dependent reactions occur?

Answer 1

Thylakoid membrane (electron transport chain)

Question 2

What are the processes of the light dependent reaction? (7)

Answer 2

1. Light energy strikes PSII an excited electrons
2. the excited e- are lost from PSII, oxidising it
3. In a series of redox reactions, the e- are transported along electron transport chain, releasing energy
4. Energy used to actively move H+ ions from stroma to thylakoids lumen
5. A chemiosmotic gradient of H+ is set up
6. H+ return to stroma down the concentration gradient through ATP synthase producing ATP from ADP+Pi
7. PSI is reduced by received electrons from the photolysis of water

Question 3

What is the chemical equation for photolysis? At photosystem I

Answer 3

H2O -> H+ + e- +O2
2H2O -> 4H+ + 4e-+O2

Question 4

What is photolsysis? And what does it do? (2)

Answer 4

Breaking down H2O by light
Photosytem is reduced by photolysis of water

Question 5

What are the processes of light independent reaction? (3)

Answer 5

1. CARBON FIXATION
   - 5C compound RuBP -> rubisco catalyses attachment of CO2 to RuBP, (6C) from forms
   - 6C compound is unstable and breaks down into two 3C compounds (GP)
2. REDUCTION of 3C compound (TP -triose phosphate)
   - converted to triode phosphate using NADPH and ATP
   - ATP hydrolysis provides energy
   - NADPH reduction transfers H+ ions to compound
3. REGENERATION OF RuBP
   - TP can be combines with organic molecules or recombines by ATP to reform RuBP stocks

Question 6

What does cyclic phosphorylation involve? (4)

Answer 6

• Use of one photosystem I doesn’t involve reduction fo NADP+
• when light is absorbed by PI, the excited electron may enter into an electron transport chain to produce ATP
• then the de-energised electron returns to photosystem restoring electron supply
• as electron returns to photosytem NADP+ is not reduced and water is not needed to replenish the electron supply

Question 7

What does non-cyclic phosphorylation involve? (4)

Answer 7

1. Involves two photsystmes and involves reduction of NADP+
2. When light is absorbed by PII and excited electrons enter into electron transport chain to produce ATP
3. photoactivation of photosystem I results in the release of electrons whic reduce NADP+ (forms NADPH)
4. Photolysis of water releases electrons which replace those lost by Photosystem II

Question 8

What are the differences between cyclic and non-cyclic phosphorylation? (5)

Answer 8

Cyclic. Non-cyclic
Only PS I involved & PS I and I involved
Water not required & photolysis of water required
Oxygen is not evolved & oxygen is evolved
NADPH not synthesised & NADPH is synthesised
Used to produce additional ATP in order to meet cell energy demands & oviducts can be used for LDR

Question 9

What do the thylakoids do in the chloroplast?

Answer 9

Flattened discs have a small internal volume to maximise hydrogen gradient upon proton accumulation

Question 10

What does the grana do in chloroplasts?

Answer 10

Thylakoids are arranged into stacks to increase SA:Vol ratio of thylakoid membrane

Question 11

What does photosystems in the chloroplasts do?

Answer 11

Pigments organized into photosystems in thylakoid membrane to maximise light absorption

Question 12

What does the stroma do in the chloroplast?

Answer 12

Central cavity that contains appropriate enzymes and a suitable pH for the Calvin cycle to occur

Question 13

What does the lamellae do in the chloroplast?

Answer 13

Connects and separated thylakoid stacks (grana) maximizing photosynthetic efficiency