Photosynthesis Flashcards
What is photosynthesis
The process where energy from light is used to make glucose from H2O and CO2
What is the overall equation of photosynthesis
6CO2 + 6H2O + energy –> C6 H12 O6 (glucose) + 6O2
What is Phosphorylation
Adding phosphate to a molecule
What is photophosphorylation
Adding phosphate to a molecule using light
What is photolysis
The splitting of a molecule using light
What is hydrolysis
The splitting of a molecule using water
What are redox reactions
Reactions that involve oxidation and reduction
OILRIG
What is a coenzyme
A molecule that aids the function of an enzyme and work by transferring a chemical group from one molecule to another
What is the coenzyme used in photosynthesis
NADP
What does NADP do
Transfers hydrogen from one molecule to another so it can reduce or oxidize a molecule
What are photosynthetic pigments
Coloured substances that absorb light energy needed for photosynthesis. They are found in the thylakoid membranes attached to proteins. e.g chlorophyll a, b and carotene
What is a protein and pigment called
A photosystem
What are the two types of photosynthetic pigments
Primary and accessory
What do primary pigments do
Are reaction centres where electrons are excited during light dependent reactions
What are accessory pigments
Make up light-harvesting systems that surround reaction centers and transfer light energy to them to boost energy avaliable for electron excitement to occur.
What is photosystem 1 best wavelength to absorb light
700nm
What is photosystem 2’s best wavelength to absorb light
680nm
How to complete chromatography to separate photosynthetic pigments
1) Grind up several leaves with anhydrous sodium sulfate and propanone
2) Transfer the liquid to a test tube and add petroleum ether and shake. Two layers should form
3) Transfer liquid from the top layer to a second test tube with anhydrous sodium sulfate
4) Draw a horizontal line on the chromatography plate, building up a single concentrated spot of liquid by adding lots of dots
5) When the origin is dry put the plate into a solvent of propane, cyclohexane and petroleum ether
6) Take the plate out and mark the solvent front allowing you to calculate the Rf value
In the light dependent reaction how is atp made
Photophosphorylation
What occurs in the non-cyclic light dependent reaction
- Light is absorbed by photosystem II exciting electrons in the chlorophyll
- The electrons move to a higher energy level so move along the electron transport chain to PS I. This meaning the electrons must be replaced so water is split into H+ ions, electrons and oxygen
- The electrons loose energy moving along the ETC which is used to transport H+ ions into the thylakoid via proton pumps.
- Protons move out into the stroma via ATP synthase and the energy from this movement combines ADP and inorganic phosphate to form ATP.
- Light energy is absorbed by PS I exciting the electrons to a higher level so they are transferred to NADP with H+ ions to form reduced NADP
What is different when cyclic photophosphorylation occurs
It only uses PS I and the electrons from the chlorophyll aren’t passed NADP but back to PS I therefore only producing a small amount of ATP
Where does the Calvin cycle occur
The stroma of the chloroplasts
What occurs in the Calvin cycle
- CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast
- It combines with RuBP (5 carbon compound) giving an unstable 6 carbon compound which breaks down into two molecules of GP
- RuBisCO catalyzes the reaction between CO2 and RuBP
- ATP and the H+ ions from reduced NADP from the light dependent reaction provides energy to turn GP to TP
- TP is converted to useful organic compounds such as glucose
- 5 out of 6 TP molecules of TP are used to regenerate RuBP
How many times does the calvin cycle need to turn before producing a hexose sugar
Six (18 ATP and 12 reduced NADP)
What are the limiting factors of photosynthesis
Light intensity, temperature and CO2 concentration
What is the optimum temperature for photosynthesis
Around 25 degrees C
What happens to the plant and therefore photosynthesis at high temperatures
- Stomata close to avoid loosing water so photosynthesis slows down
- Thylakoid membranes may be damaged reducing the number of sites avaliable for electron transfer
- The membranes around the chloroplasts could b damaged releasing enzymes for the
calvin cycle - Chlorophyll could be damaged reducing the amount of light energy absorbed.
What is the optimum percentage of CO2 concentration
0.4%
What is the saturation point of light intensity
Where by increasing the light anymore has no effect on the rate of photosynthesis
How does light intensity affect the calvin cycle
- Low light intensities the products of the light independent stage will be in short supply
- So conversion of GP to TP and RuBP is slow
- Level of GP will rise and TP and RuBP will fall
How does temperature affect the calvin cycle
- The reactions are catalysed by enzymes and at low temperatures the reactions will be slower as the enzymes will work slower.
- The levels of RuBP, GP and TP will fall
- Similar affect occurs at high temperatures when enzymes will denature
How does CO2 concentrations affect the Calvin cycle
- At low concentrations conversion of RuBP to GP is also slow
- The level of RuBP will rise and levels of GP and TP will fall
