Part 2: Photosynthesis and Primary Production

Question 1

What is photosynthesis?

Answer 1

The use of light (photons) for energy generation.

Question 2

What are the 2 stages of photosynthesis?

Answer 2

1) Light reaction (energy generation) - light is used to oxidise a substrate (water/H2S) and gain activated electrons and ATP.
2) Dark reaction (biomass synthesis) - stored energy (in ATP) and electrons are used to fix CO2 to produce organic matter.

Question 3

What are the two types of photosynthetic bacteria?

Answer 3

1) Anoxygenic phototrophic bacteria

2) Oxygenic phototrophic bacteria

Question 4

What are the characteristics of anoxygenic phototrophic bacteria?

Answer 4

• very simple photosynthetic equipment, having only one photosystem
• most can oxidise H2S–>elemental Sulphur, others use H2 or other compounds
• do not produce O2 since they cannot oxidise water (they are anaerobic)
• involved in stratified water bodies (e.g. the Black Sea)

Question 5

What are the two key groups of anoxygenic phototrophic bacteria? Give an example spp. from each.

Answer 5

1) Purple sulphur bacteria (e.g. Chromiatium okenii)

2) Green sulphur bacteria (e.g. Chlorobium limicola)

Question 6

List the six types of anoxygenic phototrophic bacteria.

Answer 6

1) Purple, non-sulphur
2) Purple, sulphur
3) Green, non-sulphur
4) Green, sulphur
5) Heliobacteria
6) AAPB

Question 7

Explain the difference between “phototrophic” and photosynthetic”. (EXAM)

Answer 7

A phototrophic bacterium use photon capture to acquire energy which can then be used to fuel metabolic processes in the cell. This does not neccessarily mean they are photosynthetic (i.e. using this energy for primary production). e.g. Aerobic anoxygenic photosynthetic bateria (AAPB) are not actually photosynthetic - they are heterotrophs.

Question 8

What are the characteristics of oxygenic phototrophic bacteria?

Answer 8

• most important biogeochemical process on Earth
• have 2 coupled photosystems, allowing greater capture of energy
• can oxidise H2O to O2
• main pigment is chlorophyll

Question 9

What are the 3 key groups of anoxygenic phototrophic bacteria?

Answer 9

1) Cyanobacteria
2) Algae/diatoms
3) Higher plants

Question 10

How have oxygenic phototrophic organisms facilitated higher life on Earth?

Answer 10

Oxygenic photosynthesis is responsible for the oxygenation of the atmosphere and formation of the ozone layer.

Question 11

How have eukaryotic photosynthetic organelles evolved?

Answer 11

They evolved from symbiotic prokaryotic cyanobacteria.

Question 12

How are oxygenic phototrophic organisms able to oxidise water to O2?

Answer 12

The redox potential of photosystem II is so strong that water can be oxidised (remember Z-scheme).

Question 13

How do bacteria avoid competition for light?

Answer 13

Different bacteria use different light spectrum niches according to their pigments.

e. g. Cyanobacteria = 450-650 nm
e. g.2 green sulphur = 650-750 nm
e. g.3 purple sulphur use 950-1050 nm

Question 14

Which organisms are responsible for the bright red colour of hypersaline environments?

Answer 14

1) Duntaliella spp. (algae)

2) Haloarchaea (bacteria)

Question 15

How are haloarchaea able to utilise light and are they photosynthetic?

Answer 15

They are phototrophic organisms (not photosynthetic). They have a pigment called bacteriorhodopsin which is in the membrane and can absorb light and pump protons through the membrane.

Question 16

Are haloarchaea photosynthetic?

Answer 16

No! They use light to generate energy but not for fixing CO2.