5.6 Photosynthesis Flashcards
Photosynthesis equation
- carbon dioxide + water + energy —> glucose + oxygen
Are plants heterotrophic or autotrophic and what does that mean
- Plants are autotrophic = makes their own food using sunlight as a source of energy = autotrophic nutrition
Is photosynthesis anabolic or catabolic
Anabolic
Is respiration anabolic or catabolic
Catabolic
What photosynthesises
Algae, fungi, plants
If bacteria doesn’t photosynthesise, what does it do
Chemosynthesis
Photoautotroph
Organisms using light as the energy source for autotrophic nutrition
Which organisms are non photosynthetic and what does that mean
HETEROTROPHS (digest complex organic molecules and using these products to get energy)
Ways autotrophs and heterotrophs rely on eachother:
Heterotrophs respire producing co2 which autotrophs rely on for photosynthesis.
- Autotrophs photosynthesise producing o2 which heterotrophs rely on for respiration
- Autotrophs are a food source (glucose)
- When heterotrophs excrete + urinate the water ends up in the sea and that water ends up being taken up by autotrophs
When do plants photosynthesise and respire
Photosynthesise during the day
Respire all the time
Compensation point
when rate of respiration = rate of photosynthesis
When do plants reach their compensation point
Different plants reach compensation points at diff times of the day
When do shaded plants reach their compensation point vs regular plants
earlier bc they’re adapted to absorb sunlight at lower light intensity
Compensation period
time taken to reach the compensation point
Inter membrane compartment
Gap between inner membrane and outer membrane of the chloroplast
Chloroplast envelope
Inner membrane + outer membrane
Where are photosystems and what are they
Thylakoids in the chloroplast + they are light harvesting centres
Chloroplast diagram
2 types of photo system
chlorophyll a = p700 (photo system 1) or chlorophyll = p680 (photo system 2)
Chlorophyll b
pigment w a wider range of wavelength absorption
What areas of light do chlorophyll a and b mainly absorb
Red and blue
What does a Photosystem look like
Photo system have primary pigment at the bottom = chlorophyll A and around it you have accessory pigments
Accessory pigments
absorbs some of the wavelength of light that chlorophylls don’t. Pass photons to the primary pigment reaction centre
Examples of accessory pigments
xanthophylls and carotenoids
Pigment
something that can absorb light at a specific wavelength
Where are photosystems found
embedded in the membrane of the thylakoids.
What do photosystems allow
the light at a range of the spectrum to be absorbed by the plant
Absorption spectrum
shows the wavelengths of light absorbed by diff pigments
Photosystem 1
- peak absorption of chlorophyll A is at a wavelength of 700nm
Photosystem 2
- peak absorption of chlorophyll A is at a wavelength of 680nm
- Comes before Photosystem 1
How to analyse pigments and accessory pigments
put it through chromatography to get the rf value
What happens when photons hit a Photosystem
Photo systems get excited by the photon (pigment molecule) hitting it and passing the energy down to the reaction centre, consisting of a type of chlorophyll.
2 stages of photosynthesis
light dependent stage and light independent stage
Stroma
fluid containing enzymes which catalyse the reactions light dependent stage
Grana
Where light dependent stage takes place
Where does the light dependent stage happen
In thylakoids
Light dependent stage diagram non cyclic
Final products of light dependent stage cyclic
Oxygen, reduced NADP, ATP
Light independent stage non cyclic
- Photon of light strikes photo system 2 and its energy goes down to the primary reaction centre. This energy is used to break water into protons, electrons and oxygen. This is known as photolysis.
- The electrons are captured by the electron transport chain, which are made up of electron carrier proteins, with fe2+ at their cores.
- As the electrons pass along the electron transport chain, some energy is released. This energy is used to pump protons across the thylakoid membrane, into the thylakoid lumen. Creating a proton concentration gradient. (Electrochemical gradient)
- Eventually the electrons are captured by Photosystem 1, where they are excited by the light energy and accepted by ferredoxin. This helps them travel from Photosystem 1 to the NADP+ in the stroma.
- The protons diffuse down their concentration gradient, through special channels associated with the enzyme ATP synthase.
- The flow of protons causes ADP + inorganic phosphate to combine, to form ATP. (Photophosphorylation)
- In the stroma, the protons and electrons combine with NADP+ to form NADPH (reduced NADP). This is catalysed by the enzyme NADP reductase.
- Final products = oxygen, reduced NADP, ATP
Where does Light dependent stage cyclic occur
In stroma fluid
Light independent stage - cyclic diagram
Cyclic photophosphorylation (light dependent stage)
- this only uses Photosystem 1. as light strikes photo system 1, electrons gain energy and get excited.
- Electrons get passed to an electron carrying system and then back to Photosystem one.
- This generates a small amount of ATP.
Why do guard cells only carry out cyclic photophosphorylation
They only have Photosystem 1 so they can only carry out cyclic photophosphorylation for a small amount of ATP to do opening and closing
What is NADP
a coenzyme which works by accepting hydrogen atoms and the enzyme it’s helping is dehydrogenase.
Chemiosmotic gradient
hydrogen ion concentration gradient
How are hydrogen ions actively transported into the thylakoid lumen
Using energy lost from electron movement
Light independent stage
Calvin cycle = carbon fixation
Where does the Calvin cycle occur
- happens in the stroma of the chloroplast
Calvin cycle stages
- Carbon dioxide from the atmosphere diffuses from the guard cells and enters the stroma.
- Carbon dioxide binds with RuBP - ribulose bisphosphate (5Carbons) catalysed by the enzyme RuBisCo (very inefficient so there’s many of this enzyme) and this produces 2GP - glycerate-3-phosphate (each have 3 carbons)
- 2GP gets converted to 2TP to do this change you need 2ATP and 2 reduced NADP
- 5/6 TP that’s made goes back to be recycled into RuBP which requires ATP
- 1/6 TP made can be converted to carbon compounds
Which carbon compounds can TP be converted to
glucose, starch, sucrose, cellulose, amino acids, fatty acids
How many cycles of the Calvin cycle is needed to make glucose
need 6 carbons so 6 cycles of the Calvin cycle
When does the Calvin cycle happen and why
during daylight bc the ATP and reduced NADP needed are produced in the light dependent stage.
- hydrogen ions from the light dependent stage are pumped into the stroma which decreases the pH to the optimum ph for RuBisCO.
- magnesium ions increases which attach to the active site of RuBisCO, acting as a cofactor.
When does RuBisCO work
optimal pH is 8 in the stroma, which only happens when the concentration of hydrogen ions decreases there, which is part of the light dependent stage. = another reason Calvin cycle only happens during daylight
Magnesium ions function in photosynthesis
Cofactor for RuBisCO
Limiting factors of photosynthesis
- co2
- water availability
- temperature
- light intensity
Why is co2 a limiting factor in photosynthesis
increasing co2, increases rate of photosynthesis
Why is water availability a limiting factor in photosynthesis
if there’s not enough water, cells lose water and become plasmolysed. The roots produce Abscisic acid which causes the stomata to close so the rate of photosynthesis will greatly decrease
Why is temperature a limiting factor in photosynthesis
lower the temperature, the slower the rate of photosynthesis
Why is light intensity a limiting factor in photosynthesis
increasing light intensity, increases rate of photosynthesis
What happens when there’s bright light
GP, TP and RuBP are all made = normal
What happens when there’s dim light
light dependent stage slows down so less NADPH and ATP is made so less GP can be converted to TP = can’t be converted to RuBP. GP accumulates, levels of RuBP and TP fall and eventually everything will stop.
What happens if there’s low co2
RuBP combines with less so less GP and TP are produced. RuBP accumulates, GP and TP levels fall
What happens when temperature increases
more respiration and more photosynthesis you have more oxygen. When oxygen levels increase it competes with carbon dioxide for enzyme RuBisCO = photorespiration (when you produce more oxygen than needed so it competes w CO2). If it competes then less GP, TP and RuBP made. Happens at temperatures above 30 degrees Celsius.
What happens at temperatures above 45 degrees Celsius
enzymes denature so the concentration of everything decreases.
How to measure the rate of Photosynthesis
- measure level of oxygen produced
- Use photosynthometer
Measuring rate of photosynthesis diagram using photosynthometer
- give the plant a few minutes to acclimatise to any changes in environment
- Same as potometer, use syringe to recalibrate the system = move meniscus back to start.
Photosynthometer practical changing conc of carbon dioxide by…
change conc of sodium hydrogen carbonate solution
Photosynthometer practical changing temperature by…
Changing temperature of water bath
Photosynthometer practical changing light intensity by…
Changing distance of a lamp
Effect of disabling proton pump in Photosystem 2
- no proton pumping = phosphorylation stops = no ATP produced = no reduced NADP produced = no carbon fixation
D
State a material that can be used as the stationary phase in thin layer chromatography.
Silica
State the precise location of photosynthetic pigments in a chloroplast.
Photosystems in thylakoid membranes
The wavelengths of light absorbed by chlorophyll c are different from those wavelengths absorbed by chlorophyll a and chlorophyll b.
Suggest why Chromista need pigments that are different from those of other photosynthetic organisms.
Have to absorb light at shorter wavelengths
How to spot the least polar pigment in TLC
Travels furthers bc is most soluble in solvent
ii
State the name of the final electron acceptor in the light-dependent stage of photosynthesis.
NADP
DCPIP turns colourless when reduced and used to investigate light dependent stage. Suggest and explain its function
Electron acceptor
Replaces NADP
What does each test tube suggest?
The student knew that it was important to use sucrose solution when homogenising the leaves.
Explain why it was important that the pellet was suspended in buffer solution and why it did not contain sucrose.
Buffer to maintain optimum pH
And no sucrose solution bc no need to prevent damage to chloroplast
How to increase validity of photosynthesis experiment’s method
Use the same light source so light intensity is controlled
Use a water bath so that temperature is controlled
ii
Explain what is meant by a limiting factor.
The factor that will limit the rate when at low level
Ways to improve experimental method and presentation of data
How to improve experimental method and presentation of data
