Unit 5 - Photosynthesis Flashcards
Autotrophs
An organism that makes their own food (complex organic compounds) from inorganic molecules using energy (chemical/ light)
Producers in an ecosystem
Chemosynthesis
Making food using chemical energy
Photoautotrophs
Organisms that photosynthesise using sunlight
Relationship between respiration and photosynthesis
All organisms respire but not all photosynthesise
Reverse processes
When do plants photosynthesise
In the day but always respire
The intensity of light has to be sufficient to allow photosynthesis to replenish carbs used in respiration
Compensation point
The rate of photosynthesis is equal to the rate of respiration
No net loss or gain of mass (carbs)
CO2 uptake in Ps = CO2 production is R
Compensation period
Time it takes to reach the compensation point
Photosystems
Particles attached to thylakoid membranes
Contain photosynthetic pigments which carry out the absorption of light in two distinct chlorophyll complexes
Photosystem I (PSI)
Funnel-shaped
Absorption wavelength is 700 nm
Found in intergranal lamellae
Photosystem II (PSII)
Funnel-shaped
Absorption wavelength is 680 nm
Found on the grana
Chlorophyll a
Reflects blue-green
Primary pigments
Found at reaction centre of both photosystems
2 forms absorb light at wavelength 680 (PSII) and 700nm (PSI) - red light
Can also absorb some blue (400nm)
Chlorophyll b
Reflects yellow - green
An accessory pigment
Absorbs light wavelengths 400-500nm (blue) and 640 (red)
Accessory pigments
Carotenoids
Xanthophyll
Chlorophyll b
Pass emitted electrons to the primary pigments which are then emitted (light harvesting pigments)
This drives photosynthesis
Carotenoids
Reflect yellow Absorb blue (400-500nm)
Xanthophyll
Reflects yellow
Absorbs blue/green (375-550)
Absorption spectrum
Results of the calorimeter test plotted on a graph
Action spectrum
Combined absorption spectra of pigments
Structure of chlorophyll molecule
Porphyrin head - hydrophilic, flat head lies parallel to thylakoid membrane for maximum absorption
Lipid soluble tail - hydrophobic, lies in thylakoid membrane
Side chains - determines which wavelengths are absorbed
Excitation of pigments by light
Chlorophyll pigments absorb light, electrons enter an ‘excited state’
This is unstable and electrons return to ‘ground state’
Lost excitation energy gets trapped during photosynthesis
Chlorophyll excitement equation
chlorophyll –> chlorophyll^+ + e^-
Reduced —-> oxidised + excited elctron
Chloroplast membrane
Both inner and outer membrane
Integranal lamellae
Extension of thylakoid membrane
Acts as skeleton
Intermembrane space
Space between membranes (10-20nm)
Granum
Stack of thylakoids
Plural grana
Stroma
Contains enzymes needed for photosynthesis, DNA and ribosomes
Thylakoids
Where the green pigment is found
Site of light absorption and ATP synthesis
Chromatogrophy table
Pigment
Distance travelled by compound
Distance travelled by solvent
Rf value
Paper chromatogrophy to seperate pigments
Dissolve pigments in solvent (propan-2-ol)
Using chromatography paper
Allow the solvent to move up the paper and seperate the pigments
Diff pigments would move at diff speeds up the paper
Calculate Rf values
Why do plants contain a mixture of diff pigments
Light is made up of many diff wavelengths
To allow plants to absorb maximum light for photosynthesis
Photophosrylation
Production of ATP in the presence of light from ADP and Pi
ATP
Adenosine tri-phosphate
Formed from inorganic phosphate and ADP during photophosphorylation
NADP
Co.enzyme reduced to NADPH by the addn. of protons and electrons at the end of the light dependent stage
Photolysis
2H2O —> 4 H+ and 4 e- and O2
H+ and e- used in photophosphorylation
O2 used in respiration and/or released
Non cyclic photophosphorylation
Involves PSII and PSI
Produces ATP, oxygen and reduced NADP
Cyclic photophosphophorylation
Involves PSI
Produces ATP in smaller amounts. No photolysis involved so no protons or oxygen produced
Process of cyclic photophosphorylation
Light hits a chlorophyll molecule in PSI and e- in primary pigment is raised to a higher energy level until it leaves
Passed along electron transport chain and energy is released in small amounts to pump H^+ into the thylakoids disc
Builds up conc. gradient
Diffuse back out through specialised channels attached to ATP synthase
Movement provides energy to combine ADP and Pi (chemiosmosis)
Non-cyclic vs cyclic photophsophophorylation
The electrons from the chlorophyll a aren’t passed onto NADP but are passed back to PSI via electron carriers
Role of chlorophyll in photolysis
It is the lost electrons from photolysis that go to the chlorophyll after absorbing light
Causes more water to dissociate
How is energy of light converted into chemical energy in the LDR
Electrons excited
Use of electrons carriers
Production of ATP
Calvin cycle
6 CO2 (+ RuBisCO) —> 12 GP (+ 12 ATP) —> 1,3 biphosphate (+12 NADPH) —> 12 TP —> 10 TP (5 ATP) —> 6 RuBP
Light Independent Stage
Only happens during the day as it needs continuous supply of products from LDR (ATP/ NAPDH)
Where does the CO2 needed in LIS come from
CO2 from respiration and other organisms (people) enter leaf through stomata
Diffuses to palisade layer then into cells then into stroma
Reactions in LIS
Carbon fixation
Reduction
Regeneration
Carbon fixation in LIS
CO2 combines w/ a CO2 acceptor (RuBP)
Reaction is ctalysed by RuBisCO
By accepting carboxylate group RuBP forms an unstable intermediate 6C compounds that immediately breaks down into GP compounds
CO2 is now fixed
Reduction in LIS
ATP reacts w/ GP to form 1,3 biphosphate which is reduced using H from NADPH into TP
Regeneration in LIS
10/12 TP molecules are rearranged into 6 RuBP using phosphate groups from ATP.
Remaining 2 TP are products and can be used to synthesise organic compounds
Use of triose phosphate
2 TP can be used to synthesise glucose
Glucose can then be converted into sucrose, starch and cellulose (or used immediately in respiration)
Synthesis of fatty acids, glycerol and amino acids
Regeneration of RuBP
Factors affecting photosynthesis
Light Intensity
CO2 conc.
Temp
Water stress
Light intensity as a factor of photosynthesis
Provides power to produce ATP and NADPH
Light allows stomata to open, enabling gas exchange
Transpiration occurs, allowing water from the roots
Molecules from Calvin Cycle in bright light
RuBP - high
TP - high
GP - low
Molecules from Calvin Cycle in dim light
RuBP - low
TP - low so RuBP cannot be regenerated
GP - high as cannot be reduced to TP
CO2 conc. as a factor of photosynthesis
CO2 levels in the atm. and aquatic habitats usually high enough to not become a limiting factor
Molecules from Calvin Cycle in high CO2
TP - High
RuBP - low
GP - high
Calvin Cycle in low CO2
RuBP - High as nothing for to acccept so it accumulates
GP - low as cannot be made
TP - low; cannot be made
Temp as factor of photosynthesis
25 - 30 degrees: rate increases
30 - 45 degrees: O2 more successfully competes w/ CO2 for active site of RuBisCO
> 45 degrees: Enzymes denature
Calvin cycle as temp increases
CO2 not accepted by RuBP (denaturing/ O2 filling binding sites)
Less GP therefore less TP
RuBP initially accumulates but doesn’t regenerate due to lack of RuBP
Non - cyclic photophosphorylation
Light is absorbed by PS2, e- in primary pigment raised to a higher energy level until it leaves PS
Travels down etc releasing energy to pump H+ into thylakoid space
Photolysis of H2O replaces e- lost from reaction centre in PS2
Light absorbed by PS1, excites e-, accepted by NADP and combines w/ excess H+ from ATP synthase
Protons accumulate in thylakoid space, membrane impermeable to H+ so diffuse down channels associated w/ ATP synthase
Measuring the rate of photosynthesis
Use a photosynthometer, measures volume of O2 produced
Use NaHCO3 as source of extra carbon
Change temp, CO2 conc. (by adding NaHCO3 to aerated water), LI (moving lamp)
Allow apparatus to equilibrate for 5 mins
Chemiosmosis
Uses an electrochemical gradient
Moving down a conc.gradient using a proton motive force
How many times does the Calvin cycle need to occur to produce 1 glucose molecule
6
