C1.3 Photosynthesis Flashcards
What is the main difference between absorption and action spectra?
Action spectra show the wavelengths of light that activate photosynthesis, absorption spectra display the wavelengths of light absorbed by a pigment.
What is photosynthesis?
The conversion of light energy into chemical energy.
It is an enzyme-catalysed metabolic pathway only used by autotrophs.
Photosynthesis equation
Water + Carbon dioxide = Glucose + Oxygen
- through light and chloroplasts
Structure of a chloroplasts and importance:
- Double membrane (outer and inner)
- chlorophyll + other pigments
- lamella
- granum
- thylakoid
- stroma
- (starch granule)
It is the sight of photosynthesis
What are the main reactions of photosynthesis? Where do they take place?
Light dependent reaction: Thylakoid
Light independent reaction: Stroma
What are the inputs and outputs of the two photosynthesis reactions?
LDepR:
- h2o + light
- o2 + h+ ions/NADH + ATP
LInR:
- co2 + NADH
- glucose (+ ADP and NAD+)
What do pigments do?
Absorb light for photosynthesis
What is an action spectrum? What are the axis?
The action spectrum measure the maximum rate of photosynthesis for different wavelengths of light
Y: rate of photosynthesis
X: wavelength (blue/700 on left and red/400 on right)
What is the absorption spectrum? What are the axis?
The absorption spectrum measures the wavelengths of light absorbed by a specific pigment.
The graph looks different depending on the pigment.
Y: absorption of light %
X: wavelength (700/blue — red/400)
Why do leaves change colour in the autumn?
The chlorophyll pigments die and it takes too much energy to keep producing them, so the other pigments that aren’t dead are shown
What is chromatography used for? How does it work?
Used to identify and separate pigments (in a leaf)?
1. mush up leaves and place the juice onto the paper
2. mark the start line with a pencil
3. place into solvent
Uses the solubility of pigments to separate them.
Why do pigments separate in chromatography?
Different pigments have different solubilities.
More soluble = travel farther
Less soluble = travel less/slower
What is an Rf value? How is it measured?
Retardation factor:
distance traveled by solute/distance traveled by solvent
What are the main steps of the LDepR?
In the THYLAKOID SPACE:
1. Photoactivation
2. Photolysis
3. ETC
4. Chemiosmosis and ATP synthesis
5. Reduction of NADP to NADPH
Explain the non-cyclic LDepR:
- Photoactivation (thylakoid):
- PSII abors light and excites e-
- PSII is oxidised and loses an e- - Photolysis:
- H2O is split (o2 is waste)
- H+ accumulate in the thylakoid space
- the e- from the splitting of H2O reduces/replaces the PSII lost e- - ETC:
- The e- are passed along carrier proteins down the membrane
- this is a series of REDOX reactions
- generates energy for proton gradient/pumping of H+ into thylakoid space - Chemiosmosis and ATP production
- H+ ions flow through ATP synthase and produce ATP - Reduction of NADP to NADPH:
- PSI receives the excited e-
- gives it to ferrodoxin (protein carrier)
- e- is used to reduce NADP to NADPH+ with the H+ ions left over from chemiosmosis/ATP synthase
What happens in the cyclic LDepR?
The production of NADPH is stopped:
- due to imbalance of ATP and NADPH production
- instead PSI send the e- to the proton pump/ATP synthase and not ferrodoxin
What are the end products of the LDepR?
O2
ATP
NADPH+
WHat are the inputs of the LInR?
ATP
NADPH+
CO2
What is the name for the process happening in LinR?
What is the product used for?
Calvin Cycle - Carbon Fixation
The LinR produces Glucose phosphate that can be
- stored as starch
- used for growth as cellulose
- used in respiration as glucose
Explain the calvin cycle:
IN THE STROMA:
- RuBP (5 carbon) is carboxylated with CO2 by Rubisco
- An unstable 6 carbon molecule is formed
- splits into two glycerate-3-phosphates
- glycerate-3-phosphate is reduced into triose phosphate
- NADPH+ and ATP are oxidised to NADP and ADP
- most of the triose phosphates are used to regenerate RuBP (5/6 cycles)
- some are used to create glucose (1/6 cycles)
What are the end products of the Calvin cycle?
- RuBP
- Glucose (-phosphate) to b changed into anything (amino acids, carbs, etc.)
- ADP (back to LDepR)
- NADP (back to LDEpR)
What is Rubisco?
The most abundant enzyme on earth.
Is used in photosynthesis
What factors can affect the rate of photosynthesis?
- CO2
- Light
- Chlorophyll
- Temperature
How does light, CO2 and pigment concentration affect photosynthesis?
- As they increase, photosynthesis increases
- Eventually reach a plateau as a different factor becomes limiting
How does temperature affect photosynthesis?
- At lower temperatures photosynthesis is slow
- Increase in temp increases photosynthesis until optimum is reached
- If temperature exceeds optimum, enzymes denature and photosynthesis stops
How can photosynthesis be measured? What would this involve?
Oxygen production:
- submerge aquatic plants in water
- attach gas syringe and measure amount of o2 produced
CO2 uptake:
- place plants in enclosed space with water
- co2 will react with water and turn it acidic
- measure change in pH
Glucose production:
- measure change in biomass
What happens to the oxygen produced in photolysis?
Excreted as waste through the stroma
Explain how there is a constant electron supply in the light dependent reactions of photosynthesis
Photolysis of water gives an electron is given to PSII to replace the one it lost
How does the structure of chloroplasts help photosynthesis?
Thylakoid: provides a large surface area for light absorption
Folds in thylakoid: allow photosystems and electron carriers to be close together
Thylakoid spaces: have low volume and quickly generates proton gradient
Stroma: contains rubisco and all other enzymes needed
Similarities between chloroplasts and mitochondria:
- membranes maximise surface area
- low volume of intermembrane spaces to quickly generate H+ gradient
- stroma and matrix have fluid needed for diffusion and containing enzymes
- membranes both have ATP synthase, e- carrier, and use chemiosmosis
- both have outer membranes that compartmentalise organelles in the cytoplasm of the cell
What is ATP synthase?
An enzyme that pumps H+ protons to make ATP.
What is needed more (for the calvin cycle)? What happens if there is an imbalance?
ATP > NADPH
Cyclic phosphorylation:
the electron oxidised by PSI is recycled instead of being used to make NADPH and goes to PSII to allow more h2o to be split and produce more ATP.
