5.1 Photosynthesis Flashcards
Which reactants/products of photosynthesis are used up/produced in the LDR?
Water (& light)
Oxygen
Which reactants/products of photosynthesis are used up/produced in the Calvin cycle?
CO2
Glucose
Where does each step of photosynthesis take place?
LDR: chloroplast (thylakoid membrane)
Calvin: stroma of chloroplast
What is a lamella and what is it made of?
Connects the grana together
Made of thylakoid membrane!
Do chloroplasts have ribosomes
YES (think enzymes embedded in the membrane - ATP synthase etc!)
Chloroplasts structure to function (x3)
- thylakoid membranes/grana: large SA for light absorption & reactions; membrane-bound enzymes & photosystems; high density of chlorophyll for light absorption
- low-volume thylakoid spaces: rapid generation of H+ gradient for chemiosmosis
- enzyme-rich stroma for CC: contains rubisco for carboxylation of RuBP; fluid for easy diffusion
Why are there different types of chlorophyll?
Not all wavelengths of light are equally absorbed, and different chlorophylls absorb more strongly in different parts of the visible spectrum
Typical chlorophyll light absorption (describe the graph)
x-axis: wavelength (red-blue)
y-axis: absorption
cosine wave (lowest at green, highest at red & blue)
Is reduced NADP an oxidising or reducing agent?
REDUCING!!
which means it itself is oxidised :)
What is a photosystem and how do they work?
Funnel-shaped structures that sit on the thylakoid membranes.
Accessory pigments absorb light of different wavelengths & pass energy down the photosystem. Eventually the energy reaches the primary pigment which absorbs a specific wavelength that acts as a reaction centre.
PSI vs PSII
PSI: absorption peak at 700nm (chlorophyll a)
PSII: absorption peak at 680nm (chlorophyll b)
LDR Stage 1
- photoionisation of chlorophyll: chlorophyll molecules in PSII absorb photons of light, exciting 2 chlorophyll electrons to a higher energy level
- this causes the electrons to move to an electron acceptor protein molecule/e- carrier
- this causes the photolysis of water (to replace the lost electrons)
Photolysis of water in more detail
2H2O = O2 + 4H+ + 4e-
What happens to each product of photolysis of water?
Oxygen produced diffuses out of chloroplast & into the air
Protons are released into thylakoid lumen
Electrons replace excited electrons that have been ejected from chlorophyll in PSII
Where is the endpoint of the electron transport chain in the LDR?
Reduced NADP/NADP reductase
LDR Stage 2
- The excited electrons pass along a chain of electron transport proteins in the thylakoid membrane
- The energy in the electrons is used to pump protons from stroma to thylakoid lumen, creating a proton gradient across the thylakoid membrane
- In PSI, more photons of light are absorbed and passed to the electrons, causing further excitation
LDR Stage 3
- The electrons are eventually recombined with some of the protons to form H atoms
- These are taken up by molecules of NADP so reducing it to reduced NADP: NADP + H+ + e- = reduced NADP
- The reduced NADP moves to the stroma for the Calvin cycle
LDR Stage 4
- The remaining protons diffuse down their gradient from the thylakoid lumen to the stroma through ATP synthase (chemiosmosis)
- This spins the enzyme, opening up its active sites and allowing the production of ATP (ADP + Pi = ATP)
What is the general name for ATP synthesis?
photophosphorylation!
because it uses light energy to phosphorylate ADP :)
What abiotic factor is the CC most prominently affected by and why?
Temperature - enzymes are involved!
What products of the LDR are used in the CC?
ATP and reduced NADP
Three steps of the CC in a nutshell
- Carbon fixation
- Reduction
- Regeneration of RuBP
How many times is ATP used in the CC, and when?
2 times
- GP converted to triose phosphate
- Triose phosphate converted to RuBP
What is another name for carbon fixation?
Carboxylation by rubisco
What happens during carbon fixation?
One molecule of CO2 binds to the 5-carbon sugar ribulose bisphosphate (RuBP) to form two molecules of the 3-carbon compound glycerate 3-phosphate (GP).
This reaction is catalysed the enzyme ribulose bisphosphate carboxylase (rubisco).
What happens during reduction?
GP is reduced/converted and activated to form triose phosphate (TP) using two ATP and two reduced NADP.
This produces 2 ADP and 2 NADP+ which go back to the thylakoid membrane to take part in the LDR.
What happens after triose phosphate is produced?
One carbon from the two triose phosphate molecules is used to make glucose, so one molecule of glucose is produced every 6 turns of the cycle.
Most of the triose phosphate is used to regenerate RuBP using ATP.
Limiting factors graphs: what are the x and y axes?
x axis: limiting factor
y axis: rate of photosynthesis
What are the four limiting factors of photosynthesis?
- Light intensity
- CO2 concentration
- Temperature
- Available chlorophyll
Why does rate of photosynthesis increase as light intensity increases?
More energy is supplied to the plant, and therefore the LDR can occur faster.
This produces more ATP and reduced NADP for the CC, which can also occur at a faster rate
Why does rate of photosynthesis increase as CO2 concentration increases?
CO2 is one of the raw materials required for photosynthesis.
It is required for the CC - CO2 combines with RuBP during carbon fixation.
This means the more CO2 is present, the faster this step of the CC can occur and the faster the overall rate of photosynthesis.
Why does rate of photosynthesis increase as temperature increases?
The CC is affected by temperature (LDR not so much - driven by light energy), as the CC consists of enzyme-controlled reactions (e.g. rubisco)
What are the benefits of using hydroponics?
- Doesn’t require as much land
- Conditions can be controlled
RP7 (chromatography): what are the four pigments from most to least soluble?
Carotene
Xanthophyll
Chlorophyll a
Chlorophyll b
