Photosynthesis Flashcards
Photosynthesis definition?
Utilisation of solar energy (photons) to synthesis organic molecules.
Phototrophs definition?
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
Examples of phototrophs
Plants, algae, cyanobacteria
What is the role of pigments in photosynthesis for ATP production?
Light sensitive pigments transform light energy into chemical energy.
Examples of light sensitive pigments for photosynthesis?
Chlorophyll
Carotenoids (absorb light from different wavelengths)
What are the two types of chlorophyll?
- Light-harvesting chlorophyll
2. Reaction-centre chlorophyll: transforms light energy to chemical energy, generating its own electron donor
What does photophosphorylation generate?
ATP
Describe the process of photophosphorylation
- 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
What are the two types of photosynthesis reactions?
- Light reaction
2. Dark reaction
Explain the light reaction in photosynthesis
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.
Explain the dark reaction in photosynthesis
Chemical reactions that don’t require light.
Includes CO2 fixation (autotrophy) and N-fixation.
Explain the role of electron donors in photosynthesis
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
Oxygenic photosynthesis reaction and PED
Dark reaction:
6H2O + 6CO2 -> 6O2 + C6H12O6
PED = H2O
PEDs used in anoxygenic photosynthesis?
Reduced molecules:
H2, S, S2O32-, H2S, Fe(II)
Definition of oxic and anoxic
Environment with or without oxygen
Definition of oxygenic and anoxygenic
Refers to the process that produces or does not produce oxygen
Definition of aerobic and anaerobic
Organisms that grow with or without oxygen
Definition of obligate aerobes or anaerobes
Organisms which can grow with or without oxygen (cant be both)
Definition of facultative anaerobes
Organisms which can grow without O2, but will use if it is present.
What are the two types of photosynthesis?
Oxygenic photosynthesis
Anoxygenic photosynthesis
Definition oxygenic photosynthesis and examples of oxygenic phototrophs
Produce oxygen.
Examples:
Algae - eukaryotic
Cyanobacteria - prokaryotic
Definition anoxygenic photosynthesis and examples of anoxygenic phototrophs
Don’t produce oxygen. Categorised by type of pigmentation and reductant (electron donor for dark reaction).
Examples:
Green/purple bacteria, heliobacteria etc.
Describe Green-Sulphur bacteria
- 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
Describe Green Non-Sulphur bacteria
- Can grow either as aerobic photoheterotrophs or anaerobic photoautotrophs
- Electron donors = sulphides e.g., H2S
e.g., Chloroflexus (thermophillic, filamentous)
Describe Purple-Sulphur bacteria
- 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
Describe Purple Non-Sulphur bacteria
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
Describe Heliobacteria
Obligate anaerobic photoheterotrophs
- can fix nitrogen
