5.6 Photosynthesis Flashcards
(93 cards)
1
Q
Photosynthesis equation
A
- carbon dioxide + water + energy —> glucose + oxygen
2
Q
Are plants heterotrophic or autotrophic and what does that mean
A
- Plants are autotrophic = makes their own food using sunlight as a source of energy = autotrophic nutrition
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Q
Is photosynthesis anabolic or catabolic
A
Anabolic
4
Q
Is respiration anabolic or catabolic
A
Catabolic
5
Q
What photosynthesises
A
Algae, fungi, plants
6
Q
If bacteria doesn’t photosynthesise, what does it do
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Chemosynthesis
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Q
Photoautotroph
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Organisms using light as the energy source for autotrophic nutrition
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Q
Which organisms are non photosynthetic and what does that mean
A
HETEROTROPHS (digest complex organic molecules and using these products to get energy)
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Q
Ways autotrophs and heterotrophs rely on eachother:
A
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
10
Q
When do plants photosynthesise and respire
A
Photosynthesise during the day
Respire all the time
11
Q
Compensation point
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when rate of respiration = rate of photosynthesis
12
Q
When do plants reach their compensation point
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Different plants reach compensation points at diff times of the day
13
Q
When do shaded plants reach their compensation point vs regular plants
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earlier bc they’re adapted to absorb sunlight at lower light intensity
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Q
Compensation period
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time taken to reach the compensation point
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Q
Inter membrane compartment
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Gap between inner membrane and outer membrane of the chloroplast
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Q
Chloroplast envelope
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Inner membrane + outer membrane
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Q
Where are photosystems and what are they
A
Thylakoids in the chloroplast + they are light harvesting centres
18
Q
Chloroplast diagram
A
19
Q
2 types of photo system
A
chlorophyll a = p700 (photo system 1) or chlorophyll = p680 (photo system 2)
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Q
Chlorophyll b
A
pigment w a wider range of wavelength absorption
21
Q
What areas of light do chlorophyll a and b mainly absorb
A
Red and blue
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Q
What does a Photosystem look like
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Photo system have primary pigment at the bottom = chlorophyll A and around it you have accessory pigments
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Q
Accessory pigments
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absorbs some of the wavelength of light that chlorophylls don’t. Pass photons to the primary pigment reaction centre
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Q
Examples of accessory pigments
A
xanthophylls and carotenoids
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Pigment
something that can absorb light at a specific wavelength
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Where are photosystems found
embedded in the membrane of the thylakoids.
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What do photosystems allow
the light at a range of the spectrum to be absorbed by the plant
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Absorption spectrum
shows the wavelengths of light absorbed by diff pigments
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Photosystem 1
- peak absorption of chlorophyll A is at a wavelength of 700nm
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Photosystem 2
- peak absorption of chlorophyll A is at a wavelength of 680nm
- Comes before Photosystem 1
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How to analyse pigments and accessory pigments
put it through chromatography to get the rf value
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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.
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2 stages of photosynthesis
light dependent stage and light independent stage
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Stroma
fluid containing enzymes which catalyse the reactions light dependent stage
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Grana
Where light dependent stage takes place
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Where does the light dependent stage happen
In thylakoids
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Light dependent stage diagram non cyclic
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Final products of light dependent stage cyclic
Oxygen, reduced NADP, ATP
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Light independent stage non cyclic
1. 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.
2. The electrons are captured by the electron transport chain, which are made up of electron carrier proteins, with fe2+ at their cores.
3. 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)
4. 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.
5. The protons diffuse down their concentration gradient, through special channels associated with the enzyme ATP synthase.
6. The flow of protons causes ADP + inorganic phosphate to combine, to form ATP. (Photophosphorylation)
7. In the stroma, the protons and electrons combine with NADP+ to form NADPH (reduced NADP). This is catalysed by the enzyme NADP reductase.
8. Final products = oxygen, reduced NADP, ATP
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Where does Light dependent stage cyclic occur
In stroma fluid
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Light independent stage - cyclic diagram
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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.
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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
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What is NADP
a coenzyme which works by accepting hydrogen atoms and the enzyme it’s helping is dehydrogenase.
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Chemiosmotic gradient
hydrogen ion concentration gradient
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How are hydrogen ions actively transported into the thylakoid lumen
Using energy lost from electron movement
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Light independent stage
Calvin cycle = carbon fixation
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Where does the Calvin cycle occur
- happens in the stroma of the chloroplast
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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
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Which carbon compounds can TP be converted to
glucose, starch, sucrose, cellulose, amino acids, fatty acids
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How many cycles of the Calvin cycle is needed to make glucose
need 6 carbons so 6 cycles of the Calvin cycle
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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.
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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
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Magnesium ions function in photosynthesis
Cofactor for RuBisCO
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Limiting factors of photosynthesis
- co2
- water availability
- temperature
- light intensity
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Why is co2 a limiting factor in photosynthesis
increasing co2, increases rate of photosynthesis
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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
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Why is temperature a limiting factor in photosynthesis
lower the temperature, the slower the rate of photosynthesis
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Why is light intensity a limiting factor in photosynthesis
increasing light intensity, increases rate of photosynthesis
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What happens when there’s bright light
GP, TP and RuBP are all made = normal
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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.
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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
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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.
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What happens at temperatures above 45 degrees Celsius
enzymes denature so the concentration of everything decreases.
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How to measure the rate of Photosynthesis
- measure level of oxygen produced
- Use photosynthometer
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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.
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Photosynthometer practical changing conc of carbon dioxide by…
change conc of sodium hydrogen carbonate solution
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Photosynthometer practical changing temperature by…
Changing temperature of water bath
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Photosynthometer practical changing light intensity by…
Changing distance of a lamp
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Effect of disabling proton pump in Photosystem 2
- no proton pumping = phosphorylation stops = no ATP produced = no reduced NADP produced = no carbon fixation
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D
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State a material that can be used as the stationary phase in thin layer chromatography.
Silica
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State the precise location of photosynthetic pigments in a chloroplast.
Photosystems in thylakoid membranes
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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
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How to spot the least polar pigment in TLC
Travels furthers bc is most soluble in solvent
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ii
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State the name of the final electron acceptor in the light-dependent stage of photosynthesis.
NADP
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DCPIP turns colourless when reduced and used to investigate light dependent stage. Suggest and explain its function
Electron acceptor
Replaces NADP
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What does each test tube suggest?
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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
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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
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ii
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Explain what is meant by a limiting factor.
The factor that will limit the rate when at low level
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Ways to improve experimental method and presentation of data
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How to improve experimental method and presentation of data
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