Photosynthesis Flashcards
1
Q
Photosynthesis
A
- Converts carbon (inorganic CO₂) into organic compounds
- Conversion of light energy to chemical energy stored in glucose and other organic compounds
- Light dependent reaction and light-independent reaction
2
Q
Chloroplast
A
- Site of photosynthesis
- Plastid containing photosynthetic pigments (chlorophyll and carotenoids)
- Has an envelope (double membrane)
- Inner membrane encloses stroma
- Thylakoids → fluid-filled membranous sacs → stacks (grana) → linked by intergranal lamellae
3
Q
Photosynthetic pigments
A
- Light receptors
- Each has a certain molecular structure that absorbs light strongly at specific wavelengths → spectrophotometer
- Chlorophyll a
- Chlorophyll b
- Carotenoids
4
Q
Chlorophyll a
A
- P680 and P700
- Different absorption peaks
- Participate directly
5
Q
Chlorophyll b
A
- Accessory pigment
- Indirect role
6
Q
Carotenoids
A
- Accessory pigments
- Indirect role
- Photoprotective role → absorb and dissipate excess light energy
- Add colour to fruits and flowers
7
Q
Absorption spectrum
A
- Plotting a pigment’s light absorption vs wavelength
- Each pigment has own specific spectrum
- Each pigment has diff no., height and breadth of peaks
- Pigments hardly absorb any green wavelengths of light
8
Q
Action spectrum
A
- Effectiveness of diff wavelengths of light in stimulating photosynthesis
- Similar to absorption spectrum, but does not exactly match that of chlorophyll a
- Chlorophyll b and carotenoids broaden spectrum of wavelength → channel energy absorbed to chlorophyll a
9
Q
Photosystem
A
- Located on thylakoid membrane
- Reaction center
- Light-harvesting complex
- Light-dependent reactions
- PS II → P680(nm)
- PS I → P700(nm)
10
Q
Reaction center
A
Protein complex that includes 2 special chlorophyll a molecules and a primary electron acceptor
11
Q
Light-harvesting complex
A
Pigment molecules bound to proteins → allow light to be harvested
12
Q
Photoactivation
A
- When chlorophyll molecule absorbs photon of light → one of the molecule’s e⁻ elevated from ground state to excited state (orbital of higher potential energy)
- Excited state is unstable → falls back to ground state → excess energy released
- Energy relayed to another pigment via resonance transfer of energy
- Electron may also be captured by primary electron acceptor
13
Q
Light-independent reaction (2)
A
- Non-cyclic → predominant route
- Cyclic
- Located on thylakoid membrane
14
Q
Non-cyclic photophosphorylation (5)
A
- Drives synthesis of NADPH and ATP
1. Photoactivation
2. Photolysis of water
3. 1st e⁻ transport from PSII to PSI + photophosphorylation
4. Light harvesting at PSI
5. Electron transport from PSI to NADP⁺
15
Q
Photoactivation (4)
A
- Photon of light strikes pigment molecule in light harvesting complex → 1e⁻ excited to higher energy level → drops to ground state → energy released passed on to next pigment molecule
- Energy relayed to other pigment molecules via resonance transfer of energy until it reaches one of the two P680 chlorophyll a molecules in the PSII reaction center
- Excites one of the P680 e⁻ to a higher energy state
- Excited e⁻ captured by primary e⁻ acceptor → e⁻ hole left in PSII
16
Q
Photolysis of water (4)
A
- Enzyme splits water molecule into 2e⁻, 2H⁺ + ½O₂
- e⁻ supplied to P680 molecules → replace e⁻ lost to primary electron acceptor/fill e⁻ hole
- O atom combines with another to form O₂ → by-product
- H⁺ remains in thylakoid space → contributes to high [H⁺] in thylakoid space