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
