Photosynthesis

Question 1

What are the two types of photosynthesis?

Answer 1

Oxygenic photosynthesis - electron donor: H20, by-product: O2 (plants, algae, cyanobacteria)

Anoxygenic photosynthesis - electron donor: H2S, by-product: elemental S (green/purple ulcer bacteria)

Question 2

What are the two phases of photosynthesis?

Answer 2

Light reactions - photosynthetic electron transport chain // conversion of light energy into chemical energy —> ATP & NADPH

Carbon reactions - CO2 fixation (“dark” reaction / Calvin cycle)

Question 3

Chlorophyll is the main … pigments

Answer 3

light-absorbing

Question 4

What is the structure of a chlorophyll?

Answer 4

1. Tetrapyrrole ring (porphyrin)
2. Metal cofactor (centre of porphyrin)
3. Phytol tail (long, hydrophobic side chain, non polar)

Question 5

Phycobilins is the main … in cyanobacteria & red algae

Answer 5

pigment

Question 6

What is the structure of phycobilins?

Answer 6

1. Linear tetrapyrroles
2. No metal cofactor
3. No phytol tail

Question 7

The light in photosynthesis can return in 3 different ways, which ways?

Answer 7

1. Relaxation - lost as heat
2. Fluorescence - lost as light of longer wavelength
3. Transfer - to neighbouring pigment

Question 8

What is Anoxygenic photobionts?

Answer 8

One photosystem

Question 9

What is Oxygenic photobionts?

Answer 9

Two photosystems

Question 10

What is the Z-scheme?

Answer 10

How the two photosystems work together to convert light into ATP

Question 11

Describe the photosynthetic electron transport chain

Answer 11

Works in series - two different photosystems (I & II) —> absorbs a certain amount of light —> energy of light is transferred from one chl-molecule to another —> arrives to the reaction centre
—> special chlorophyll (PSII = P680), all excitation energy —> high energy state —> lose energy = lose electron —> PS has a net positive charge from losing an electron —> gains an electron from the oxidation from H2O

Question 12

What is the photophosphorylation?

Answer 12

Light-dependent synthesis of ATP

Question 13

There are two multiprotein segments in the ATP synthase, which are they?

Answer 13

1. Transmembrane complex - CF0
2. Hydrophilic extrinsic complex - CF1

Question 14

What happens in the carbon cycle (Calvin cycle)?

Answer 14

Photosynthetic carbon fixation (in Stroma)

Question 15

How many steps/phases does the C3 calvin cycle include?

Answer 15

13 steps / 3 phases

Question 16

Describe the three C3 Calvin cycle phases.

Answer 16

1. Carboxylation (1 reaction): CO2 + RuBP —> 3-PGA
2. Reduction (2 reaction) (required ATP & NADPH): 3-PGA —> triose phosphate (GAP)
3. Regeneration (10 reactions) (Requires ATP): GAP —> RuBR

*Calvin cycle needs more ATP than NADPH

Question 17

What happens to the triose phosphate? (C3)

Answer 17

First used for these biosynthetic pathways in photosynthetic cells (source cells)

Question 18

What happens to the excess triose phosphate? (C3)

Answer 18

Transported as sucrose —> transported through the phloem from source (leaf) to sink cells

Question 19

Where does CAM photosynthesis occur?

Answer 19

Common in plants that inhibit extremely arid areas

Problem - How to avoid water loss in a hot & dry habitat and still photosynthesis?
Solution - temporal separation of CO2 uptake & fixation

Night: stomata open - CO2 —> malate
Day: stomata closed - malate —> CO2 + pyruvate (Calvin cycle)