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Geomicrobiology > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Photosynthesis definition?

A

Utilisation of solar energy (photons) to synthesis organic molecules.

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2
Q

Phototrophs definition?

A

Organisms that photosynthesise.

  • Use light as energy source
  • electron donors are not for energy production, they’re used in anabolism, so not PEDs
  • either inorganic or organic carbon source
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3
Q

Examples of phototrophs

A

Plants, algae, cyanobacteria

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4
Q

What is the role of pigments in photosynthesis for ATP production?

A

Light sensitive pigments transform light energy into chemical energy.

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5
Q

Examples of light sensitive pigments for photosynthesis?

A

Chlorophyll

Carotenoids (absorb light from different wavelengths)

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6
Q

What are the two types of chlorophyll?

A
  1. Light-harvesting chlorophyll

2. Reaction-centre chlorophyll: transforms light energy to chemical energy, generating its own electron donor

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7
Q

What does photophosphorylation generate?

A

ATP

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8
Q

Describe the process of photophosphorylation

A
  • chlorophyll absorbs light
  • absorption reduces the electrode potential of the reaction centre by the amount of energy of the photon
  • makes the reaction centre more electronegative, turning it into an electron donor
  • electrons are transferred stepwise to TEAs along the electron transport chain (ETC)
  • allows for ATP synthesis
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9
Q

What are the two types of photosynthesis reactions?

A
  1. Light reaction

2. Dark reaction

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10
Q

Explain the light reaction in photosynthesis

A

Light energy (photon) is absorbed by chlorophyll and transformed to ATP.

It is like catabolism part of metabolism, but not true catabolism as ATP is transformed not actually produced.

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11
Q

Explain the dark reaction in photosynthesis

A

Chemical reactions that don’t require light.

Includes CO2 fixation (autotrophy) and N-fixation.

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12
Q

Explain the role of electron donors in photosynthesis

A

Photoautotrophs fix CO2 (produce organic carbon, but use inorganic carbon).

  • This is done by internal reductants.
  • Internal reductants are reduced by electrons from the environment.
  • Electron donors are not PEDs and not part of catabolism, rather used in anabolism
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13
Q

Oxygenic photosynthesis reaction and PED

A

Dark reaction:
6H2O + 6CO2 -> 6O2 + C6H12O6

PED = H2O

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14
Q

PEDs used in anoxygenic photosynthesis?

A

Reduced molecules:

H2, S, S2O32-, H2S, Fe(II)

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15
Q

Definition of oxic and anoxic

A

Environment with or without oxygen

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16
Q

Definition of oxygenic and anoxygenic

A

Refers to the process that produces or does not produce oxygen

17
Q

Definition of aerobic and anaerobic

A

Organisms that grow with or without oxygen

18
Q

Definition of obligate aerobes or anaerobes

A

Organisms which can grow with or without oxygen (cant be both)

19
Q

Definition of facultative anaerobes

A

Organisms which can grow without O2, but will use if it is present.

20
Q

What are the two types of photosynthesis?

A

Oxygenic photosynthesis

Anoxygenic photosynthesis

21
Q

Definition oxygenic photosynthesis and examples of oxygenic phototrophs

A

Produce oxygen.

Examples:
Algae - eukaryotic
Cyanobacteria - prokaryotic

22
Q

Definition anoxygenic photosynthesis and examples of anoxygenic phototrophs

A

Don’t produce oxygen. Categorised by type of pigmentation and reductant (electron donor for dark reaction).

Examples:
Green/purple bacteria, heliobacteria etc.

23
Q

Describe Green-Sulphur bacteria

A
  • Strictly anaerobic
  • Use inorganic sulphur as electron donor e.g., H2S
  • Found in sulphur rich, anoxic environments
  • Can grow syntrophically with SRB

CO2 -> CH2O
H2S -> S

24
Q

Describe Green Non-Sulphur bacteria

A
  • Can grow either as aerobic photoheterotrophs or anaerobic photoautotrophs
  • Electron donors = sulphides e.g., H2S

e.g., Chloroflexus (thermophillic, filamentous)

25
Q

Describe Purple-Sulphur bacteria

A
  • Have red/purple carotenoid pigments
  • Found in deep water where IR radiation is filtered, still some light reaches.
  • Electron donors = H2S, H2, Fe(II)
  • Grow heterotrophically or chemolithoautotrophically with or without O2.

CO2 -> CH2O
H2S -> S

e.g., Chromatium

26
Q

Describe Purple Non-Sulphur bacteria

A

Similar to PSB, but can’t survive environments with too much H2S.
Therefore, not found in same environment as GSB and PSB.
Grow as photoheterotrophs
- use organic carbon as C source

Organic Compound -> CH2O
H2S -> S

e.g., Rhodospirillium

27
Q

Describe Heliobacteria

A

Obligate anaerobic photoheterotrophs

- can fix nitrogen

Geomicrobiology (14 decks)

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