5.6 Flashcards
What is the compensation point?
When photosynthesis and respiration occurs at the same rate.
What is a photosystem?
Found in thylakoids of chloroplasts
System of 300 molecules of chlorphyll which trap photons and pass energy into primary pigment reaction centre during light dependent stage.
What are the two forms of cholorphyll a
- P680 in PS2
- P700 in PS1
What is photolysis?
Splitting of water
4H+
4e-
O2
Function of water?
- Produces oxygen
- Replaces electron lost in chlrophyll
- source of protons used in phtoto phosphorylation
- Plant cells turgid
Explain the process of non-cyclical photophosphorylation?
1) Light energy captured by PS2 (P680) which is channelled to primary reaction centre exciting electrons.
2) These electrons escape and are captured by electron carrier chain which contains iron
3) Electron associates with iron and then oxidates causing it to be released to next electron.
4) This process produces energy which is used to actively pump protons from thylakoid membrane into thylakoid space.
5) The electrons lost in PS2 are replaced by electrons produced from photolysis.
6) Electrons then pass onto PS1 (P700) where it combines with electron transport chain feradoxin which passes the electrons to NADP in the stroma.
7) As protons accumulate there is a gradient formed which causes them to move back out via a protein channel with ATP synthase which produces ATP by catalysing a reaction between ADP and free phosphates
8) Electrons are passed through and associate with NADP producing reduced NADP
9) ATP and reduced NADP are to be used in LIS of photosynthesis.
What occurs during cylical photphosphorylation?
1) Light strikes PS1, pair of electrons become excited
2) Pass onto Electron carrier
3) Produce little ATP during passage along electron carrier
4) ATP used to actively pump potassium ions into cells, lowering water potential so that water follows via osmosis
5) Water causes guard cells to swell and stomata to open
Explain the calvin cycle
1) Carbon dioxide combines with RuBP (Rubisco biposhphate) to become carboxylated. Catalysed by RubisCO
2) This forms an unstable 6 carbon molecule which breaks down to 2 molecules of GP (phosphate) which is fixed.
3) These are reduced using electron from reduced NADP to TP
4) 5/6 TP rearranged to RuBP
What are the uses of TP?
- Glucose converted into sucrose and starch
- TP used to synthesise amino acids, fatty acids and glycerol
What is effect of light intensity on Calvin cycle?
- GP can not be reduced to TP
- GP accumulates, TP falls
- Without TP, RUBP can not be regenerated
What is effect of carbon dioxide on Calvin cycle?
- RuBP cannot be accpeted and accumulates
- GP can not be made
- TP can not be made
