photosynthesis Flashcards
What happens during photoionisation
Light is absorbed by chlorophyll
This excites electrons to move into chlorophyll
Electrons enter electron transport chain
chlorophyll becomes positively charged
What are the thylakoid membranes?
Folded membranes which contain photosynthetic proteins (chlorophyll) and electron carrier proteins embedded within these membranes which are both involved in LDR
What are the stroma?
Fluid centre which contains enzymes involved in the LIR
What are the stroma?
Fluid centre which contains enzymes involved in the LIR
What are the roles of the inner and outer membrane in chloroplast
Control what Can enter and leave the organelle
Where does the LIR occur
Stroma
Where does the LDR occur
Thylakoid membranes/ grana
State the 4 stages of light dependent reaction
1) Photolysis
2) photoionisation of chlorophyll
3) chemiosmosis
4) production of ATP and reduced NADP
What happens in the Photolysis of water and what stage is it
1st stage
Light energy is absorbed by chlorophyll and splits water into O2, protons (hydrogen ions) and electrons
Protons picked up by NADP = NADPH (used in LIR)
Electrons are passed along chain of electron carrier proteins
Oxygen either used for respiration or diffuses out of stomata
What happens in Photoionisation of chlorophyll?
Light energy is absorbed by chlorophyll and the energy results in electrons becoming excited and raising up an energy level to leave chlorophyll
=chlorophyll has been ionised by light
Some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis
What happens during chemiosmosis?
Electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane
As move along proteins they release energy, some of energy used to pump protons from stroma across chloroplast membrane (proteins) into thylakoid lumen
= electrochemical gradient built up
= protons move by facilitated diffusion back down CON GRAD to stroma ( by ATP SYNTHASE)
= enables atp synthase (enzyme) to phosphorylate ADP to ATP
Protons back in stroma
NADP enzyme picks up electrons from end of electron transport chain + protons after passing through ATP synthase
= reduces NADP
Why is the LIR temperature sensitive?
The stroma contains enzyme Rubisco Which catalysed the reaction.
What compounds does the Calvin Cycle use and why?
CO2, reduces NADP, ATP
ATP is hydrolysed to provide energy for reaction
Rescued NADP donated the hydrogen to reduce molecules GP
What happens in the Calvin Cycle (LIR)
CO2 reacts with ribulose bisphosphate (RuBP) = 2molecules of glycerine 3phosphate (GP) - a 3 carbon compound
That reaction is catalysed by enzyme RUBISCO
GP is then rescued to TP using energy from ATP and by accepting a hydrogen from reduced NADP = NADP
Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances
The rest of the molecule is used to REGENERATE RuBP (energy from ATP)
Whilst glucose is the product - Calvin cycle needs to happen 6 times to produced glucose(or any hexose sugar) - monosaccharide Can join to from disaccharides (sucrose / polysaccharides like cellulose and starch).
Can convert into glycerol - combine with fatty acids = lipids for plants
Why can CO2 be classified as a limiting factor for photosynthesis?
Because CO2 is a reactant in the Calvin cycle
What is light intensity classified as a limiting factor?
Light energy is needed in LDR for photolysis and photoionisation
The monitoring of limiting factors
Agricultural practises for maximum photosynthesis
Artificial lighting - max light intensity
Heating a greenhouse - increase temperature
Burning fuel - release more CO2
Each technique needs to be consider in terms of profit
If extra growth from photosynthesis is minimal, it won’t be COST EFFECTIVE to pay for
What is the sim of the Calvin’s experiment
To measure the incorporation of carbon 14 isotope into carbohydrate molecules
Trace movement of carbon through Calvin cycle
Visualise the distribution of radioactivity in plant material
Equipment used in Calvin experiment and it’s Role
Funnel - add algae
Syringe - inject radioactive carbon isotope (CO2)
Hot methanol - denature enzymes and stop reaction
Rapid action tap - get samples at precise time and rapidly in quick succession (into hot methanol)
Analyse quantity of radioactive carbon in all different molecules (how much carbon isotope in each molecule)
Flat Lollipop - flat on both sides gives larger SA = more of algae exposed to light = rate of LDR faster
Explain why each stage of Calvin experiment is done
Isolation of chloroplasts - homogenise sample of cells + centrifuge to isolate
Incorporation carbon 14 - carbon injected into apparatus, leave for set of time under conditions = allow co2 fully incorporated into all carbon containing compounds
Perfusion of chloroplasts - simulstsneuodly continue to inject carbon14 isotope as co2 through rapid action tap = multiple sample at precise times and measure exact quantity of carbon isotope in all carbon containing compounds
Measurement of radiosctvity - using radiography, mesure quantity of radioactive substances in carbon containing compound
Why is there a high amount of radioactive substance in GP in the light than RuBP?
GP is 3 carbon compound but have 2 GP molecules within Calvin cycle
Only have one RuBP (5 carbon compound
= ALWAYS gonna have higher amount of radioactivity in GP than RuBP because it contains more carbons (carbon is radioactive)
Why does the amount of glucose decrease and amount of GP increase in the dark?
Un every tune of the Calvin cycle one of the carbons from TP goes towards making hexose sugar (glucose)
Dark - LDR stop = no NADPH or ATP
These r required in Calvin cycle to reduce GP into TP
= increase in GP and decrease in TP
= glucose decreases (since it is a hexose sugar made by joining 2 TP molecules)
Why does RuBP levels decrease in the dark?
RuBP is still able to combine with CO2 (using rubisco) = GP
GP isn’t converting into TP
= no TP available to regenerate RuBP
ALSO no ATP available to regenerate TP into RuBP
