Photosynthesis

Question 1

Give the chemical equation for photosynthesis.

Answer 1

CO2 + H20 > (CH2O) + O2

Question 2

Give the name for the photosynthetic membranes.

Answer 2

Thylakoids.

Question 3

Give a brief overview of the stages of photosynthesis.

Answer 3

Light photon absorbed by pigments.
Energy used to drive an e- from water to generate NADPH.
Movement of e- down a protein transport chain drives protons across the membrane.
These protons generate ATP synthesis when they diffuse back down the chemiosmotic gradient into the stroma through ATP synthase.

Question 4

Why do we need to generate ATP & NADPH?

Answer 4

Used in the light-independent stage to fix CO2.

Question 5

What are the 4 nitrogen atoms in chlorophyll bound to?

Answer 5

1 Mg ion.

Question 6

What is the difference between different chlorophylls?

Answer 6

They have a different R group.

Question 7

What happens to the energy of a photon when it is absorbed by the chlorophyll network?

Answer 7

It is exciton transferred to the reaction centre chlorophyll a.
Or an e- excited from the harvesting chlorophyll is transferred to the reaction centre.

Question 8

What is exciton transfer?

Answer 8

An excited chlorophyll passes its energy to an adjacent chlorophyll molecule.

Question 9

Describe a photosynthetic unit.

Answer 9

Has a large network of chlorophyll molecules.

2 types, ~300 antenna chlorophylls & 1 reaction centre chlorophyll.

Question 10

Which chlorophylls in a photosynthetic unit undergo photochemistry?

Answer 10

Only the RC chlorophyll.

Question 11

What is the turnover rate of the RC?

Answer 11

100x per sec, but only 1 photon per sec directly hits RC, so antenna chlorophylls increase capacity.

Question 12

What happens when the RC is excited?

Answer 12

an excited e- is transferred to an acceptor molecule.

Question 13

What is photoinduced charge separation?

Answer 13

donor of e- becomes +ve, acceptor molecule becomes -ve. occurs at the special pair of chlorophylls in the RC.

Question 14

PSI responds to wavelengths of…

Answer 14

< 700nm

Question 15

PSI responds to wavelengths of…

Answer 15

< 680nm

Question 16

What protein is attached to PSII & what is its function?

Answer 16

oxygen evolving complex
splits water to produce an e- to replace the e- lost at RC.
also produces H+ that adds to overall proton gradient.

Question 17

Give the flow of electrons through the etc.

Answer 17

e- derived from water, excited at RC of PSII
PSII > quinone pool
Quinone pool > cytochrome bf
Cytochrome bf > plastocyanin
Plastocyanin > PSI

Question 18

What is a quinone pool?

Answer 18

quinone that can move freely through membrane.

reduced by e- & move to transfer this to cytochrome bf.

Question 19

What does ferredoxin do?

Answer 19

transfers e- to NADP reductase to make NADPH.

Question 20

How many photons need to be absorbed to make 2 NADPH molecules?

Answer 20

8 hv.

Question 21

Which experiment showed that the proton gradient was responsible for making ATP?

Answer 21

Jagendorf acid bath experiment.

Question 22

Describe the Jagendorf acid bath experiment.

Answer 22

thylakoid membranes soaked in pH 4 buffer for several hours.
then were rapidly submerged in pH 8 buffer containing ADP & Pi.
inside the thylakoid membrane initially remained pH 4.
burst of ATP production noted simultaneously to the loss of that pH gradient.

Question 23

How is mit. ATP synthase different to chloroplast ATP synthase.

Answer 23

Orientation reversed:
H+ flow out of thylakoid lumen
H+ flow into mit. matrix

Question 24

Give the 1st step of the Calvin Cycle.

Answer 24

5C Ribulose phosphate + CO2 > short-lived 6C intermediate

Question 25

Give the 2nd step of the Calvin Cycle.

Answer 25

6C intermediate breaks down into 2x 3-Phosphoglycerate (3C)

Question 26

Give the 3rd step of the Calvin Cycle.

Answer 26

2x 3-Phosphoglycerate (3C) gets phosphorylated using 3 ATP > 2x 1,3- Biphosphoglycerate (3C)

Question 27

Give the 4th step of the Calvin Cycle.

Answer 27

2x 1,3- Biphosphoglycerate (3C) gets reduced using 2 NADPH > 2x Glyceraldehyde-3-phosphate (3C).

Question 28

Give the 5th step of the Calvin Cycle.

Answer 28

G3P is recycled 5/6 times back into Ribulose Bisphosphate.
1/6 times it is used for biosynthesis.
3 turns of the cycle.

Question 29

How much ATP & NADPH does 1 G3P molecule used for biosynthesis require?

Answer 29

9 ATP & 6 NADPH

Question 30

Give the full name of Rubisco.

Answer 30

Ribulose Bisphosphate Carboxylase Oxygenase.

Question 31

What is the purpose of Rubisco?

Answer 31

capture CO2 to allow it to be fixed.

reacts it with ribulose bisphosphate.

Question 32

Give the key enzymes that regulate the Calvin Cycle& where they are located.

Answer 32

Rubisco
Fructose 1,6 Bisphosphatase
Sedoheptulose 1,7 Bisphosphatase
all located in the stroma.

Question 33

How are the Calvin Cycle enzymes regulated?

Answer 33

inactive in dark when stroma pH is 7
active in light, at their optimal stroma pH of 8
rise in pH caused when H+ are pumped into lumen.
causes Mg+ to leave lumen into the stroma, Mg activates all 3 enzymes.

Question 34

How does ferredoxin regulate the Calvin Cycle?

Answer 34

a protein that conveys e- out of PSI usually to give to NADP reductase.
but it can use the e- to reduce thioredoxin.
reduced thioredoxin can give the e- to reduce the enzymes, reactivating them.
in inactive state a disulphide bridge forms between 2 cysteine residues.