3.5.1 - Photosynthesis Flashcards
Howmany stages does photosynthesis have ?
2 - the light dependent reaction and light - independent reaction.
Where does photosynthesis occur ?
The chloroplast of the plant cell, but in different locations.
Where do the LDR and LIR occur?
LDR - on the thylakoid membraines/ grana
LIR - occurs in the stroma
What is the LDR ?
The first stage of photosynthesis, requiring light.
Light energy and H2O are used to created ATP and NADPH for the LIR.
What is photolysis?
Equation ?
The splitting of water by light energy
2H2O –> O2 + 4e- + 2H+
What are the different substances in photolysis used for ?
H+ : picked up by NADP to form NADPH and is used in the LIR
e- : Passed along a chain of electrons by carrier proteins
O2 : respiration or diffuses out
Process of LDR (1) - Photosystem 2
- Light at the red - blue/violet end of the spectrum hits the magnesium ion
- Causes electrons to become excited as the energy level increases
- Chlorphyll is oxidsied, PA will become reduced
- The high energy e- is transported down an ETC via sequential redox reactions.
- The energy is transferred to a proton pump, accumulates H+ against a con grad
- This flows through ATP synthase
- The proton motive force allows ATP synthase to synthesise ATP from ADP + Pi
Describe the process of photosystem 1
- Light at the red blue/violet hits the Mg ion in the chloroplast and photoionisation takes place.
- The energy level of the e- is raised and it is lost from the chlorophyll. The chlorophyll is oxidised and the PA in the ETC is reduced.
- The e- is transported down the ETC via sequential oxidation/reduction reactions
- The electron is taken up by NADP reductase which turns NADP and a proton into NADPH
What is the LIR also known as ?
The Calvin Cycle
Where does the Calvin Cycle occur?
What does it contain ?
The stroma
It contains the enzyme RuBisCo which catalyses this reaction
What are the roles of ATP and NADPH in this reaction ?
ATP when it is hydrolysed provides energy for the reaction, the NADPH donates the H+ to reduce the molecules of GP in the cycle.
Process of the Calvin Cycle (LIR)
- CO2 reacts with RUBP to form two molecules of GP and this reaction is catalysed by Rubisco.
- GP is reduced to TP using energy from ATP and by accepting a H from NADPH.
- From the two molecules of TP produced, 1 of the C atoms is removed each time the cycle turns
- When the cycle has occured 6 times, a hexose sugar is formed.
- The left over 5 carbons are used to regenerate RUBP.
Howmany carbons do each of these compunds have :
- RUBP
- Hexose sugars
- GP
- TP
- 5c
- 6c
- 3c per molecule so 6 in total
- 3c per molecule so 6 in total
What does TP form when it leaves the cycle ?
Useful organic substances
What are some useful organic (carbon containing compounds) that the hexose sugars may form ?
- Disaccharides - sucrose
- Polysaccharides - cellulose and starch
- Glycerol, and then it can combine with fatty acids to make lipids
- AAs for proteins and nucleic acids - DNA and RNA
What are the limiting factors of photosynthesis ?
Temperature
Carbon dioxide concentration
Light intensity
How does temperature affect the rate of photosynthesis ?
This affects the LIR due to it being enzyme controlled
- too cold - not enough energy
- too hot - denatured
How does CO2 affect the rate of photosynthesis ?
- Has an effect on the LIR due to it being one of the reactants entering the Calvin Cycle.
How does light intensity affect the rate of photosynthesis ?
- It is required for the LIR for it to hit the magnesium ion for photoionsiation to take place
- It is also needed for photolysis to take place.
What does knowledge of limiting factors allow ?
Allows farmers to have the understanding of what conditions to manipulate in which they grow their plants.
What are some ways in which farmers manipulate conditions ?
- Artificial lighting of the maximum intensity
- Heating the greenhouse to increase temperature
- Burning fuel (i.e, paraffin burners) to release more CO2
What does the farmer have to consider within their agricultural practices ?
The profit
- To pay for lighting, heating, fuel, the farmer must consider the cost
- Whatever he is paying, is he getting more profit for it ?
