Photosynthesis 2

Question 1

The special pair of chlorophylls in the reaction centre of PSII undergo ?

Answer 1

Undergo five states of oxidation.

Only the S4 state is capable of water oxidation

Question 2

Trimeric LHC-II and Lhcb 3, 4, 5, and 6 are normally found localized around ?

Answer 2

PSII reaction centre complexes

Question 3

Photosystem reaction centres are surrounded by?

Answer 3

Antenna complexes containing chlorophyll a and b. They absorb photon energy and transfer energy to the neighbouring light harvesting molecules. The absorbed photon energy is funnelled down to the reaction centre.

Question 4

Chlorophyll a is found in all reaction centre complexes as well as in antennae, whereas Chlorophyll b is only found in ?

Answer 4

Antenna complexes

Question 5

Explain β-carotene absorption ?

Answer 5

• Carotenoids have a triple banded absorption spectra in the region 400- 500 nm.
• Their main function is to dissipate the excess energy of excited triplet chlorophyll and to detoxify reactive O2 species (ROS).
• Carotenoids also participate in protecting chlorophylls from photo-oxidation damage as accessory pigments

Question 6

What are some common carotenoids ?

Answer 6

Carotenes and Xanthophylls

• β-carotene - a carotene, hydrocarbon (no oxygen), insoluble in water
• Lutein – a xanthophyll, contains oxygen, less hydrophobic

Question 7

Carotenoids dissipate the excess ?

Answer 7

Energy of excited primary pigments

Question 8

What are the possible fates of the “excited” electron in the chlorophyll molecule ?

Answer 8

1. The e-can relax to a lower quantum state, transferring energy as heat.
2. The e-can relax to a lower quantum state and transfer energy into fluorescence.
3. The energy can be transferred by resonance (RET) to a neighboring molecule as the e-returns to a lower quantum state.
4. The excited e- can be lost to an e- acceptor at a different redox potential (charge separation) with the chlorophyll molecule becoming in turn an e-acceptor.

Question 9

Thylakoid membranes are the site of ?

Answer 9

Light harvesting

Question 10

The arrangement of the photosynthetic ETC complexes is not ?

Answer 10

Homogenous

Question 11

Difference between where PSII complexes and ATP synthase is found ?

Answer 11

PSII complexes are found more densely localised where the granal lamellae are appressed whereas ATP synthases and PSI are observed in the membranes that are nonappressed and are directly facing the stroma

Question 12

The photosystems are linked by e- carriers which when arranged according to their redox potentials form ?

Answer 12

A Z-shape

Question 13

Ferredoxin is ?

Answer 13

A relatively small soluble, iron/sulfur (Fe2S2) protein

Question 14

Ferredoxins are iron-sulfur proteins that transfer ?

Answer 14

Electrons in a wide variety of metabolic reactions

Question 15

FDX1 is ?

Answer 15

A small (14-kD), soluble Fe2S2 electron shuttle protein that resides either free in the mitochondrial matrix or is loosely bound to the inner mitochondrial membrane

Question 16

FD2 resides in ?

Answer 16

The chloroplast and is a soluble Fe2S2 electron shuttle protein at the stroma side of the thylakoid membrane

Question 17

No NADPH and O2 ?

Answer 17

No carbohydrate synthesis

Question 18

What are some stresses the plant face ?

Answer 18

• Drought
• High light
• Low CO2
• Greater demand for ATP relative to NADPH