Unit 13: Photosynthesis (JW) Flashcards
describe the relationship between the structure of chloroplasts
- Thylakoid for LDS
- Thylakoid membranes contain ATP synthase, ETC for chemiosmosis
- Grana = stacked thylakoids - increase SA for maximum light absorption
- Contain photosynthetic pigments arranged in photosystems
- Primary pigment surrounded by accessory pigments
- Accessory pigments pass energy to primary pigments
- Different pigments absorb diff wavelengths
- Stroma for LIS
- Stroma contains water as reaction medium
- Contains enzymes, e.g. rubisco, sugars, ribosomes, DNA
- DNA/ribosomes to synthesise proteins required for ptsts
- Starch grains - store carbohydrates
Describe the functions of the internal membranes of the chloroplast in photosynthesis. (7)
Has photosynthetic pigments to absorb light energy directed to photosystems
Then results to photoactivation due to light energy, passes through ETC releasing energy to establish proton gradient, which internal membranes are impermeable for so can maintain
So photophosphorylation, has ATP synthase to synthesise ATP by chemiosmosis
It’s also where photolysis occurs
Thylakoids stacked to form grana
Large surface area
Explain how grana are adapted for their specific role in ptsts.
- Stacks of thylakoids = increased SA for pigments = increased light absorption
- Photosynthetic pigments to absorb maximum light energy
- ETC to release energy from excited e-
- Photosystems & reaction centre are light harvesting structures
- Thylakoid space forms proton gradient
- Thylakoid membrane relatively permeable to maintain proton gradient
- ATP synthase -> make ATP
- Contains OEC for photolysis of water
- Many enzymes, e.g. ETC, ATP synthase
- For LDS
What is energy transferred as from the LDS?
When & where is it used?
ATP & reduced NADP
during LIS
reduces GP to form TP
Site of LDS & LIS?
LDS Site: Thylakoids (thylakoid membrane + spaces) -> occur in stacks called grana
LIS Site: Stroma
describe the role of
1. photosynthetic pigments in general
2. accessory pigments
Photosynthetic Pigments:
- absorb light energy
- Excite electrons
- Photophosphorylation
- Accessory pigment passes energy to primary pigment from photosystem
Accessory pigments:
- Chlorophyll b / carotene
- Absorb light energy
- Pass on light energy to chlorophyll a in rxt centre
- Absorb different wavelength of light compared to chlorophyll a
- Combined pigments absorb greater range of wavelengths
- Pigments absorb different WLs of light to maximise light absorbed for ptsts
- Increases rate of LDS
- More growth
Describe action spectrum and absorption spectrum
- Action spectrum shows rate of ptsts @ different light WLs
- Absorption spectrum shows absorption of different wavelengths
- Higher absorption = higher rate of ptsts
describe and use chromatography to separate and identify chloroplast pigments
- Grind leaf
- Use solvent
- Leaf extract contains mixture of pigments
- Draw pencil line on chromatography paper
- Drop extract on pencil line, dry and drop repeatedly to produce concentrated extract
- Paper suspended vertically in beaker of solvent
- Solvent allowed to travel up chromatography paper
- Different pigments travel at different speeds
- Pigments separated by their solubility as they rise up
- Use ruler to measure distance moved by each pigment and solvent
- Calc Rf value = dist travelled by pigment / dist travelled by solvent
- compare Rf value to published Rf values to identify pigments
- cover solvent to prevent evaporation
What 2 aspects make up LDS?
LDS = CP + NCP
Describe cyclic photophosphorylation
- Only PS I involved
- Light energy absorbed by (accessory) pigments (& passed onto chlorophyll a)
- e- excited
- e- emitted from PS I
- ETC -> energy released -> pump H+ into thylakoid space against conc gradient
- chemiosmosis (H+ move by FD down CG back to stroma through ATP synthase)
- ATP synthesis
- e- returns to PSI
- pigments arranged in light-harvesting clusters
- chlorophyll a in reaction centre
- accessory pigments surround chlorophyll a (primary pigment)
- PS located in thylakoid
Describe non-cyclic photophosphorylation
- Both PS I & II involved
- Photolysis of water, forming H+, e- and O2 catalysed by Oxygen-evolving complex enzyme
- H+ released from PS II
- e- released from PS I
- e- and H+ combine to form hydrogen atom
- Combines with NADP to form reduced NADP
- Hydrogen atom of reduced NADP used to reduce GP to TP
- LIS takes place in the stroma
Describe similarities and differences between cyclic & non-cyclic photophosphorylation.
Similarities:
- Photoactivation of chlorophyll
- ETC involved
- ATP produced
Differences:
- C only PS I, whereas NC involved BOTH PS I & II
- C only prod ATP, whereas NC prod BOTH ATP and reduced NADP
- C does NOT involve photolysis of water, whereas NC does
- e- emitted from PS I in C, whereas e- emitted from PS II are replaced by water in NCP
- In CP, e- emitted returns to same photosystem
- In NCP, Oxygen produced
- In NCP, e- emitted from PS II absorbed by PS I
Describe the role of PS II in the absorption of light
LHC
accessory pigments - e.g. chlorophyll b, carotene
pass light to reaction centre/chlorophyll a
NCP
more and different WL absorbed
Outline the Calvin Cycle
- CO2 fixation with RuBP
- catalysed by rubisco
- unstable 6C compound formed
- x2 mlcls of GP formed
- GP reduced to TP using ATP & reduced NADP from LDS
- TP combines with nitrate ions
- TP regenerated to RuBP (involving ATP)
- Ions enter via roots against CG using ATP
What are Calvin cycle intermediates used to produce?
- GP used to form AA
- TP used to form glucose
- condensation/glycosidic bonds form to produce starch, cellulose etc.
Outline the uses of TP in mesophyll cells of the leaf.
- Regenerates RuBP (involving ATP)
- for respiration
- Makes glucose/ribose/deoxyribose/glycerol
State and explain the limiting factors of photosynthesis
Limiting factor:
- Ptsts controlled by several factors
- Limiting factor is factor nearest its minimum value / in shortest supply
- Prevents increase in rate of ptsts
- Light intensity, CO2 conc, temperature
Temperature:
- Higher temp = higher ptsts rate
- Temperature affects photophosphorylation
- Enzymes may denature at high temps too
- Low temp decrease rate of ptsts
- Low temp decrease ESC formations
- Low temp is limiting factor
Light intensity:
- light energy / photons ;
2 for, light-dependent stage / photophosphorylation / photolysis / photoexcitation / photoactivation ;
3 to make, reduced NADP / ATP ;
4 to open stomata (for CO2 to enter) ;
When describing limiting factor graphs..
- At low conc, (factor) is limiting factor
- At higher conc, (another factor) becomes limiting factor (graph levels off) - factor no longer becomes limiting
- Explain why (factor) is required for ptsts
explain the effects of changes in light intensity on the rate of photosynthesis
When temp & CO2 conc constant -> changes in light intensity affects rate of ptsts
low LI = limiting factor
rate of ptsts increases, as light intensity increases
greater light intensity = more light energy absorbed = faster LDS
more ATP & reduced NADP for Calvin cycle -> greater rate of LIS
If light intensity continues to increase, relationship no longer applies -> graph pleateaus
Light intensity no longer LF - another factor (temp, CO2 conc) becomes LF
explain the effects of changes in carbon dioxide concentration on the rate of photosynthesis
CO2 conc increases, rate of ptsts also increases
Required for LIS when CO2 fixated with RuBP
More CO2 = faster Calvin Cycle = faster overall rate of ptsts
Trend continues until another factor (LI, temp) become limiting factor - preventing rate from increasing further
explain the effects of changes in temperature on the rate of photosynthesis
Temp increases = rate of ptsts also increases
as ptsts controlled by enzymes
trend only continues up to certain temp
beyond which enzymes begin to denature = rate of ptsts decreases
Temp no significant effect on LDS as driven by light energy, rather than KE
Calvin Cycle affected by temp as LIS are enzyme-controlled (rubisco catalyses carbon fixation)
Explain why carbon dioxide produced at low light intensities
- Little ptsts occurring
- Due to low light intensity
- Rate of respiration > rate of ptsts
describe and carry out investigations using redox indicators, including DCPIP and methylene blue, and a suspension of chloroplasts to determine the effects of light intensity on the rate of photosynthesis
DCPIP takes up e-
changes from blue to colourless when becomes reduced
The rate of colour change = rate of ptsts
Leave crushed in an isolation medium - concentrated leaf extract - containing suspension of intact and functional chloroplasts
medium must have same water potential as the leaf cells
medium must contain buffer to keep pH constant
medium must be ice-cold to avoid damaging chloroplasts & maintain membrane structure
small tubes set up with diff light intensities - same wavelength (colour of light)
DCPIP added to each tube + small volume of leaf extract
record time taken for DCPIP to turn colourless
1/time taken = rate of ptsts
describe and carry out investigations using redox indicators, including DCPIP and methylene blue, and a suspension of chloroplasts to determine the effects of light wavelength on the rate of photosynthesis
Hill reaction
Oxidised DCPIP is blue
goes colourless when reduced
prepare chloroplast extract
Buffer solution to control pH
Expose chloroplasts + DCPIP to wavelength of light
Measure time for DCPIP to change colour
Calculate rate (1/t)
Test atl. 5 wavelengths
repeat atl. 3 times for each wavelength + calc mean
Plot wavelength on x-axis and calculated rate on y-axis
Explain the effect of light intensity and time taken to decolourise DCPIP.
- As light intensity increases, time taken to decolourise DCPIP decreases
- More light energy absorbed
- More photolysis
- More e- excited
- More H+ released
- Faster reduction of DCPIP
describe and carry out investigations using whole plants, including aquatic plants, to determine the effects of temperature on the rate of photosynthesis
- Gas syringe
- Cut shoot of aquatic plant
- Place shoot in tube of hydrogen carbonate solution to provide CO2
- Water bath to maintain temperature
- Atl. 5 different temperatures
- Acclimatisation
- Lamp placed fixed distance away
- Count num of air bubbles produced in set time
- repeat atl. 3 times at each temperature
- Calc mean for each temp
- Calc rate of ptsts (mean num of air bubbles produced / time period)
describe and carry out investigations using whole plants, including aquatic plants, to determine the effects of light intensity on the rate of photosynthesis
Ensure water well aerated by bubbling air through it
Ensure plant has been well-illuminated before use - ensure plant contains all enzymes needed for ptsts - any changes are due to independent variable
Set up apparatus in darkened room
cut stem of pondweed cleanly before placing into boiling tube
measure vol of gas collected in gas syringe
for same period of time (e.g. 5 mins)
Change dist of light source from plant - atl. 5 different distances from plant
Same temperature (thermostat. cont. WB)
*Glass filled with water placed in between plant & lamp - prevent heat reaching plant - keep temp constant
Same CO2 conc - same volume sodium hydrogencarbonate solution (1%) - controlled supply of CO2
repeat atl. 3 times at each distance + calculate mean vol of O2 produced
Record results in table
plot a graph of volume of O2 produced per min against independent variable
calc rate of ptsts (vol of O2 produced / minute)
describe and carry out investigations using whole plants, including aquatic plants, to determine the effects of carbon dioxide concentration on the rate of photosynthesis
Ensure water well aerated by bubbling air through it
Ensure plant has been well-illuminated before use - ensure plant contains all enzymes needed for ptsts - any changes are due to independent variable
Set up apparatus in darkened room
cut stem of pondweed cleanly before placing into boiling tube
measure vol of gas collected in gas syringe
for same period of time (e.g. 5 mins)
same light intensity: same dist of light source from plant
Same temperature (thermostat. cont. WB)
different volumes of sodium hydrogencarbonate solution to water surrounding plant - atl. 5 diff volumes (e.g. ….)
*Glass filled with water placed in between plant & lamp - prevent heat reaching plant - keep temp constant
repeat atl. 3 times at each CO2 conc + calculate mean vol of O2 produced
Record results in table
plot a graph of volume of O2 produced per min against independent variable
calc rate of ptsts (vol of O2 produced / minute)
Describe the role of other photosynthetic pigments found in plant chloroplasts.
- Chlorophyll b / carotene
- Accessory pigments
- Absorb light energy
- Pass on light energy to chlorophyll a
- Absorb different wavelength of light compared to chlorophyll a
Explain why membrane C has many different coloured pigments to function efficiently.
- Absorb light energy
- Different wavelengths of light can be absorbed
- Increase LDR
- Chlorophyll a, b and carotene
Describe how you would carry out chromatography to separate and identify the coloured pigments in the liquid extract of C.
- Spot placed on pencil line
- Repeat above
- Paper suspended in solvent
- Mark solvent front after some time -> remove paper
- Calc Rf value = dist moved by pigment / dist moved by solvent
- Comp Rf value to known Rf values to identify pigments
State 2 molecules that can be produced from these TP molecules.
- Glucose/fructose
- Sucrose/maltose
- Starch/cellulose
- AA
- Glycerol/fatty acids
Describe the functions of the internal membranes of the chloroplast in photosynthesis. (7)
Photosynthetic pigments to absorb light energy which is directed to photosystems
Electrons become excited due to light energy
Passed along ETC to release energy
Photophosphorylation
Site of photolysis
Thylakoids stacked to form grana
Large surface area
Thylakoid space to establish proton gradient
Thylakoid membrane is relatively impermeable to maintain proton gradient
ATP synthase to synthesise ATP by chemiosmosis
Suggest an explanation for the effect of RA on the activity of rubisco.
- RA activates rubisco
- by changing AS of rubisco
- enabling rubisco to bind more readily with RuBP
- Enables products to leave active site more quickly
Explain relationship between absorption spectrum and action spectrum of photosynthesis.
- Action spectrum shows rate of ptsts for light wavelengths
- Absorption spectrum shows how much wavelength absorbed
- Higher absorption = higher rate of ptsts
Explain why temp can be limiting factor of ptsts.
- Higher temp = higher ptsts rate
- Temperature affects photophosphorylation
- Enzymes may denature at high temps too
- Enzymes
Outline how light-independent stage of ptsts leads to production of carbohydrates.
- RuBP joins with CO2 -> GP
- GP -> TP which requires ATP and reduced NADP
- TP -> glucose
- Condensation (glucose, starch, cellulose)
Explain how grana are adapted for their specific role in ptsts.
- Stacks of thylakoids = increased SA for pigments = increased light absorption
- Photosynthetic pigments to absorb light energy
- ETC to release energy from excited e-
- Photosystems & reaction centre are light harvesting structures
- Thylakoid space forms proton gradient
- Thylakoid membrane relatively permeable to maintain proton gradient
- ATP synthase -> make ATP
- Contains OEC for photolysis of water
- Many enzymes, e.g. ETC, ATP synthase
- For LDS
Outline the method you would use to separate and identify the pigments present in an extract.
- Chromatography
- Place spot of pigment on base line (pencil line)
- Dry & repeat to concentrate spot
- Dip paper into solvent so solvent travels up paper
- Use ruler to measure dist travelled by solvent & each pigment
- Calc Rf value = dist travelled by pigment / dist travelled by solvent
- Compare Rf values against published values to identify pigments
- Cover to stop evaporation of solvent
Describe how you would separate chloroplast pigments using chromatography.
- Grind leaf
- Use solvent
- Leaf extract contains mixture of pigments
- Draw pencil line on chromatography paper
- Drop extract on pencil line and dry repeatedly to produce concentrated extract
- Paper placed vertically in beaker of solvent
- Solvent allowed to travel up chromatography paper
- Different pigments travel at different speeds
- Pigments separated by their solubility as they rise up
- Use ruler to measure distance moved by each pigment and solvent
- Calc Rf value = dist travelled by pigment / dist travelled by solvent
Outline the way in which hydrogen is made available to reduce NADP in LDS of ptsts.
- Photolysis of water
- Photosystem II
- Oxygen evolving complex enzyme
- H+ and e- combine to form hydrogen
Describe the process of cyclic photophosphorylation and the structure of the photosystem involved.
- Only PS I involved
- Light energy absorbed
- e- excited
- e- emitted from chlorophyll
- ETC
- chemiosmosis
- ATP synthesis
- e- returns to PSI
- pigments arranged in light-harvesting clusters
- chlorophyll a in reaction centre
- accessory pigments surround chlorophyll a (primary pigment)
- PS located in thylakoid
Describe the role of accessory pigments in ptsts.
- Pass light energy to chlorophyll a
- Absorb different wavelengths to chlorophyll a in photosystem
- Combined pigments absorb greater range of wavelengths
- Increases rate of LDS
- More growth
Describe the role of photosystem II in light absorption.
- Light harvesting complex
- Accessory pigments
- Channel light to chlorophyll a in reaction centre
- Different wavelegnths of light used
Describe the role of chloroplast pigments in light absorption.
- arranged in light-harvesting clusters
- Photosystems
- Accessory pigments surround primary pigment
- e.g. carotene, chlorophyll b
- Primary pigment is chlorophyll a
- in reaction centre
- Accessory pigments absorb light energy at different wavelengths to chlorophyll a
- Accessory pigments pass energy onto chlorophyll a in reaction centre
- Pigments absorb different WLs of light to maximise light absorbed for ptsts
Explain how the results of chromatography would be used to confirm that phycoerythrin (pigment) is present in red algae and not present in a plant with green leaves
- Calc Rf values
- Compare Rf values of pigments
- Find pigment present only in red algae, and not green plant
- Identify pigment using reference values
Describe the role of photosynthetic pigments
- Absorb light energy
- Excite electrons
- Photophosphorylation
- Accessory pigment passes energy to primary pigment from photosystem
Outline main features of cyclic photophosphorylation.
- Light energy electrons in PS1
- e- passed on to ETC
- energy released used to pump H+ into thylakoid space against conc gradient
- H+ move by FD down CG back to stroma through ATP synthase
- Synthesise ATP
Describe the relationship between the function of a chloroplast and its structure.
- Thylakoid for LDS
- Thylakoid membrane contains ATP synthase, ETC
- Grana = stacked thylakoids - increase SA for maximum light absorption
- Stroma for LIS
- Stroma contains water as reaction medium
- Stroma contains enzymes e.g. RuBP
- DNA/ribosomes to synthesise proteins required for ptsts
- Starch grains - store carbohydrates
Describe how the structure of a chloroplast is related to its functions.
- Stroma for LIS
- Contains enzymes, e.g. rubisco, sugars, ribosomes, DNA
- Thylakoids for LDS
- Grana = stacks of thylakoids
- Contain photosynthetic pigments
- Large SA for max. light absorption
- Pigments arranged in photosystems
- Primary pigment surrounded by accessory pigments
- Accessory pigments pass energy to primary pigments
- Different pigments absorb diff wavelengths
- Thylakoid membranes contain ATP synthase, ETC for chemiosmosis
Role of reduced NADP in light independent stage
- Reduces GP to TP
Explain how non-cyclic photophosphorylation produces reduced NADP and how reduced NADP is used in the light independent stage.
- Both PS I & II involved
- Photolysis of water, forming H+, e- and O2
- H+ released from PS II
- e- released from PS I
- e- and H+ combine to form hydrogen atom
- Combines with NADP to form reduced NADP
- Hydrogen atom of reduced NADP used to reduce GP to TP
- LIS takes place in the stroma
Outline the uses of TP in mesophyll cells of the leaf.
- Regenerates RuBP
- for respiration
- Makes glucose/ribose/deoxyribose/glycerol
Name the biochemical process that produces reduced NADP and ATP.
Photophosphorylation
Outline the reactions occurring in the stroma that lead to the production of polysaccharide, such as alginate.
- CO2 binds to RuBP
- Rubisco catalyses binding
- Forms unstable 6C compound
- Splits into 2 molecules of GP
- GP reduced to TP using reduced NADP & ATP
- TP used to form glucose
- condensation/glycosidic bonds form to produce starch, cellulose etc.
Outline how Calvin cycle produces TP and outline the conversion of TP into AA.
- CO2 fixation with RuBP using rubisco
- 6C unstable compound formed
- x2 mlcls of GP formed
- GP reduced to TP using ATP & reduced NADP from LDS
- TP combines with nitrate ions
- Ions enter via roots against CG using ATP
State 3 different functions of organic compounds that TP is used to make.
- Cellulose: cell wall
- Glucose: respiration
- Starch: energy store
- AA: protein synthesis
- Nucleic acids: store genetic information
Describe similarities and differences between cyclic & non-cyclic photophosphorylation.
Similarities:
- Photoactivation of chlorophyll
- ETC involved
- ATP produced
Differences:
- C only PS I, whereas NC involved BOTH PS I & II
- C only prod ATP, whereas NC prod BOTH ATP and reduced NADP
- C does NOT involve photolysis of water, whereas NC does
- e- emitted from PS I in C, whereas e- emitted from PS II are replaced by water in NCP
Explain how Calvin cycle is affected when rubisco denatures.
- Less CO2 fixation
- Less GP converted to TP
- Less regeneration of RuBP
- Less glucose made
Describe and explain the effect of light wavelength on the rate of LDS of ptsts.
- Highest at -
- Lowest at -
- Chlorophyll absorbs blue and red light best, but does not absorb green
- Accessory pigments
- Light excites electrons
Explain the effect of light intensity and time taken to decolourise DCPIP.
- As light intensity increases, time taken to decolourise DCPIP decreases
- More light energy absorbed
- More photolysis
- More e- excited
- More H+ released
- Faster reduction of DCPIP
Wavelength graph descriptions
- Highest & lowest peak at ()nm
- Chlorophyll absorbs best (blue & red), does not absorb green
- ## Wavelengths of light used for ptsts
Function of glass filled with water placed in between plant and lamp
- Stops heat from reaching plant
- Keeps temp constant
- as temp affects rate of photosynthesis
Function of sodium hydrogencarbonate
- Provide CO2
Explain what is meant by the term limiting factor and explain how knowledge of limiting factors is used to increase crop yields in glasshouses.
- Ptsts controlled by several factors
- Limiting factor is factor nearest its minimum value / in shortest supply
- Prevents increase in rate of ptsts
- Light intensity, CO2 conc, temperature
Factor that has no effect on reducing ability of chloroplast suspension.
- Carbon dioxide conc
- Not involved in LDS
Describe how you would carry out an investigation into the effect of wavelength of light on the rate of photosynthesis of a plant, using a redox indicator such as DCPIP.
Hill reaction
Oxidised DCPIP is blue
goes colourless when reduced
prepare chloroplast extract
Buffer solution to control pH
Expose chloroplasts + DCPIP to wavelength of light
Measure time for DCPIP to change colour
Calculate rate (1/t)
Test atl. 5 wavelengths
repeat atl. 3 times for each wavelength + calc mean
Plot wavelength on x-axis and calculated rate on y-axis
Describe how you would carry out an investigation into the effect of temperature on the rate of photosynthesis of an aquatic plant.
- Gas syringe
- Cut shoot of aquatic plant
- Place shoot in tube of hydrogen carbonate solution to provide CO2
- Water bath to maintain temperature
- Atl. 5 different temperatures
- Acclimatisation
- Lamp placed fixed distance away
- Count num of air bubbles produced in set time
- repeat atl. 3 times at each temperature
- Calc mean for each temp
- Calc rate of ptsts (mean num of air bubbles produced / time period)
Limiting factor graphs
- At low conc, (factor) is limiting factor
- At higher conc, (another factor) becomes limiting factor
- Explain why (factor) is required for ptsts
Explain the importance of minimising temperature changes.
- Control variable
- Low temp decrease rate of ptsts
- Low temp decrease ESC formations
- Low temp is limiting factor
- High temp decrease rate of ptsts as
Explain why different colour filters result in different rates of ptsts.
- Different wavelengths of light absorbed by different pigments
- Red light is absorbed the most
- Green light least absorbed
- Shorter wavelength, greater energy
- More light energy absorbed = more LDS
Explain why carbon dioxide produced at low light intensities
- Little ptsts occurring
- Due to low light intensity
- Rate of respiration > rate of ptsts
Explain why graph levels off ?
- (Factor) no longer a limiting factor
- LF is now (2 other factors)
Explain how very dry conditions cause CO2 concentration to become the main limiting factor of photosynthesis in plants.
Decrease in CO2 moving into air spaces
ABA secreted as stress response
Ca2+ is second messenger
Causing stomata to close
Suggest and explain why Sox4 plants have a higher plant biomass?
- Increased expression of SBPase gene
- Increased regeneration of RuBP
- Increased Calvin Cycle
- More glucose, starch, cellulose, AA
- More cell division
Describe the effects on a plant if its environmental temperature rises well above the usual temperature range.
- Decrease in rate of ptsts
- Rubisco denatured
- Less/no CO2 binds to RuBP
- Increase in transpiration
- Loss of turgidity
- ABA production
- Stomata close
- Reduced CO2 uptake
- Photorespiration occurs
Outline the differences between cyclic and non-cyclic photophosphorylation.
- PS I takes part in CP, but PS II does not
- e- emitted returns to same photosystem
- In NCP, e- emitted from PS II absorbed by PS I
- In NCP, reduced NADP produced
- In NCP, Photolysis occurs - only involves PS II
- In NCP, Oxygen produced
Outline the process of cyclic photophosphorylation
PS I only
LE absorbed by accessory pigments
pass onto chlorophyll a
e- become excited
emitted from PS I
ETC -> ER
chemiosmosis -> ATP synthesised
e- returns to chlorophyll
Describe the role of PS II in the absorption of light
LHC
accessory pigments - e.g. …
pass light to reaction centre/chlorophyll a
NCP
more and different WL absorbed
State the role of reduced NADP in the light independent stage
Carries H
enables reduction of GP to form TP
State and explain the expected relationship between light intensity and time taken to decolourise DCPIP
As light intensity increases, time taken decreases
more light energy absorbed
more photolysis of water
More H+ and e-, thus more H
more reduction of DCPIP
Explain how the structure of grana is linked to its function.
Stack of thylakoids
increased SA
for pigments/PS/LHC
for absorption of maximum LE
many enzymes/ETC/ATP synthase
for LDS
Explain why light intensity above range is not limiting the rate of ptsts
Other factor (LI, CO2 conc) becomes limiting factor
Low KE -> fewer collisions between rubisco and CO2
Less fixation of CO2
all enzymes already at highest rate / optimum
Distinguish between absorption spectrum and action spectrum
Absorption spectrum: shows absorption of different wavelengths
Action spectrum: shows rate of photosynthesis @ different WLs
Explain the shape of the curve as light intensity increases from 0 to X
Respiration rate > ptsts rate
net production of CO2
At point X, rate of respiration = rate of ptsts
Explain how very dry conditions cause CO2 concentration to become the main limiting
factor of photosynthesis in plants.
decrease in / no, CO2, diffusing / moving, to air spaces / palisade cells / mesophyll cells / chloroplasts / stroma ;
2 stress response / AW ;
3 ref. to abscisic acid / ABA ;
4 ref. to action of Ca2+ as a second messenger ;
5 stomata close
