Photosynthesis

Question 1

What is the equation for photosynthesis?

Answer 1

CO2 + H2O –(light)—> (CH2O) + O2

Question 2

What are the 2 stage processes in photosynthesis?

Answer 2

2H2O —(light)—-> O2 + 4[H*]

4[H*] + CO2 —–> (CH2O) + 4H2O

Question 3

Where does photosynthesis occur?

Answer 3

The chloroplast

Question 4

What are the 6 key points about a chloroplast?

Answer 4

1. 5um long
2. 1 to 1000 per cell
3. Impermeable inner barrier
4. Permeable outer membrane
5. Stroma contrains carbohydrate enzymes
6. Thylakoid is a highly folded vesicle

Question 5

What is the structure of a chloroplast? (7)

Answer 5

Chloroplast envelope
Thylakoid (membrane and space)
Stroma
Grana
Strach granules
Nuceloid
Ribosomes

Question 6

What is the principle photoreceptor?

Answer 6

Chlorophyll

Question 7

What is chlorophyll also known as?

Answer 7

Light harvesting complex

Question 8

How is light energy transferred to chemical energy?

Answer 8

Electromagnetic radiation is propagated as ‘photons’ (photooxidation)

Question 9

What are the 2 reaction centres in photosynthesis and what do they do?

Answer 9

Photosystem 2 - oxidises H2O (P680)

Photosystem 1 - reduces NADP+ (P700)

Question 10

How do electron pass from PS2 to PS1?

Answer 10

Electron transport chain

Question 11

What light does PS1 respond to and what does this stimulate it to do?

Answer 11

<700nm

Creates biosynthetic reducing power in the form of NADPH

Question 12

What does the cytochrome b6f complex do? (3)

Answer 12

Electrons travel from PS2 to PS1
Homologous to complex 3 (oxidative phosphorylation)
Generates a H+ gradient

Question 13

What light does PS2 respond to and what does this stimulate it to do? (3)

Answer 13

<680nm
Generates a molecule of O2
Transfers e- from H2O to plastoquinone
Generates a H+ gradient

Question 14

What is the structure of PS2 and where is it located?

Answer 14

Large protein assembly - 20 subunits
Thylakoid membrane (Stroma/ TM / Lumen)

Question 15

What are the key processes that occur in PS2?

Answer 15

Catalyses that transfer of e- from H2O to plastoquinone

P680+ (light) extracts e- from H2O

Question 16

What is the equation in PS2?

Answer 16

2Q + 2H2O –(light)—> O2 + 2QH2

Question 17

Why are electrons transferred from H2O to QH2?

Answer 17

QH2 e- are at a higher redox than in H2O

Question 18

How does light P680nm extract e- from H2O? (4)

Answer 18

• Oxygen evolving complex
• Each time photon kicks electron from P680, e- are extracted from Mn
• 4 photons absorbed to extract 4 e-
• 4 e- used to reduce Q2 to QH2

Question 19

What is occurs in PS2 that is vital for e- transfer?

Answer 19

Proton gradient

Question 20

What does the cytochrome bf complex do?

Answer 20

Catalyse the transfer of e- from QH2 to plastocyanin

Question 21

What occurs in the 2nd half of the Q cycle? (3)

Answer 21

Cytochrome bf reduces plastoquinone to plastoquinol

• takes up 2 H+
• oxidation, 2H+ released on stromal side

Question 22

What is the proton gradient aided by?

Answer 22

Enzyme positioning

Question 23

What is the structure and location of PS1?

Answer 23

Transmembrane complex - 14 polypeptides

Thylakoid membrane

Question 24

What are the 3 activities that happen in PS1?

Answer 24

1. E- from P700
2. Ferredoxin contains FeS centre, transfers e- to NADP+
3. P700 captures e- from reduced PC

Question 25

What happens once the electron is captured from P700? (2)

Answer 25

Travels down through the chlorophyll to the FeS cluster

Transferred to ferredoxin

Question 26

What happens once an electron isn transferred to ferredoxin? (3)

Answer 26

• Transfer of e- to NADP+
• Catalysed by ferredoxin-NADP+ reductase
• Uptake of protons occurs on the stromal side (enhance gradient)

Question 27

What is the Z scheme? (4)

Answer 27

1. P680 captured and excited e- passes up PS2
2. e- turns into QH2 down the middle z and binds with cytochrome b6f
3. P700 e- is excited in PS1
   2NADPH produced

Question 28

What occurs in photophosphorylation? (3)

Answer 28

• transmembrane proton gradient occurs
• This capitalised on by the chloroplast ATP synthase
• Photosynthesis with non-cyclic transport produces 1 ATP per absorbed photon

Question 29

What is produced from chloroplast ATP synthase?

Answer 29

1 ATP for every 3 protons

Question 30

How do plants harness energy from CO2?

Answer 30

Calvin cycle (dark reactions)

Question 31

Explain the Calvin cycle steps (6):

Answer 31

1. Ru5P binds with CO2
2. Produces 3PG
3. ATP and NADPH are added in
4. This produces GAP (glycerolaldehydes- 3 -phosphate)
5. Carbs are released
6. Ru5P reforms

Question 32

How much ATP and NADPH is used in the Calvin cycle?

Answer 32

9 ATP

6 NADPH

Question 33

How is CO2 fixed in a plant?

Answer 33

Ribulose bisphosphate carboxylase

Question 34

How is the Calvin cycle stimulated? (2)

Answer 34

pH increases

Mg2+ efflux stimulates RuBP

Question 35

What inhibits RuBP carboxylase?

Answer 35

2-carboxyarabinitol-1-phosphate

Question 36

What is the overall equation of photosynthesis?

Answer 36

3CO2 + 9ATP + 6NADPH —> GAP + 9ADP + 8Pi + 6NADP+

Question 37

What is the primary product of photosynthesis and what is it used for (2)?

Answer 37

GAP

• Used in pathways inside & outside the chloroplast
• Can be converted to fructose-6-phosphate

Question 38

What is the starch component of photosynthesis and where is it synthesised?

Answer 38

a-amylose

Synthesised in the stroma

Question 39

What else is also produced from photosynthesis?

Answer 39

Sucrose and cellulose