5.2.1: Photosynthesis Flashcards
Photosynthesis is a form of
autotrophic nutrition
Compensation point
when rate of photosynthesis = rate of respiration
Chloroplast adaptations
- Thylakoid membrane highly folded into many grana –> high SA for photosynthetic pigments, electron carriers and ATP synthase
- Photosynthetic pigments arranged into photosystems –> enables maximum adsorption of light energy
- Chloroplast DNA and 70s ribosomes –> can immediately make some of the proteins needed for photosynthesis
What are the two stages of photosynthesis?
- Light-dependent stage
* Light-Independent stage
Light dependent stage summary
- Energy from light absorbed, used to form ATP
- hydrogen from water used to turn NADP into reduced NADP
- oxygen is a by-product of this stage
Light independent stage summary
- Hydrogens from reduced NADP combined with CO₂ to build organic molecules e.g. glucose
- ATP supplies the energy required for this
What is a photosynthetic pigment?
- a pigment that absorbs light of a specific wavelength. Different pigments absorb different wavelengths of light.
- Can release excited electrons once it has absorbed light
- Used in the light-dependent stage of photosynthesis
- Located in photosystems on the thylakoid membrane
What is a light harvesting system?
Photosynthetic pigments and proteins
What is a photosystem?
Light harvesting system and the reaction centre
What is the role of the light harvesting system?
To absorb light of different wavelengths and transfer this energy to the reaction centre.
Non-cyclic photosphorylation uses which photosystem(s)?
1 and 2
Cyclic photophosphorylation uses which photosystem(s)?
1
Non-cyclic photophosphorylation produces
- ATP ( by chemiosmosis from ETCs 1 &2)
- Reduced NADP (from PS1 ETC)
- Oxygen as a by-product of photolysis
Cyclic photophosphorylation produces
• ATP by chemiosmosis
✖️ Does not produce reduced NADP
Photolysis (equation)
H₂O ⟶ 2H⁺ + 2e⁻ + ½O₂
What happens to the e- produced in photolysis?
They replace the e- last from the PS2 reaction centre.
What happens to the H⁺ produced in photolysis?
- Released into the lumen of the thylakoid
- Diffuse back through membrane down concentrations and electrochemical gradient (driving ATP formation in the process)
- Once H⁺ returned to stroma, combine with NADP and an e- from PS1 to form reduced NADP
- This combining with NADP removes H⁺ ions from the stroma, maintaining the proton gradient across the thylakoid membrane
Products of the light dependent stage that are needed for the light independent stage
- ATP
* Reduced NADP
Where does the light independent stage take place?
In the stroma of the chloroplast
Where does the light dependent stage take place?
On the thylakoid membrane
The light dependent stage uses what as a raw material?
Water
The light independent stage uses what as a raw material?
Carbon dioxide
Three main stages of the Calvin cycle?
1) Fixation
2) Reduction
3) Regeneration
Differences between cyclic and non-cyclic photophosphorylation
Non-cyclic
• O₂ produced through photolysis
• Reduced NADP produced
• Uses PS1 & 2
Cyclic
• No O₂ produced
• No reduced NADP produced
• Uses PS1 only
How many turns of the Calvin cycle are required to make one glucose molecule?
6
• Because per turn, 2 x TP produced
• 1 of every 6 TP goes towards glucose
Uses of triose phosphate (TP)
- Starting material for synthesis of carbohydrates, lipids, amino acids
- For regeneration of RuBP
What is Ribulose bisphosate carboxylase (RuBisCO)?
Enzyme that catalyses the reaction between RuBP and CO₂ to form an unstable intermediate.
What is RuBP?
Ribulose bisphosphate: five carbon molecule used in the Calvin cycle.
