Photosynthesis Flashcards
What is light harvesting?
- absorption of light energy by accessory pigments and the passing of the energy to the reaction centre chlorophyll a molecule
- the chlorophyll a molecule uses the energy to excite e-s - drives light dependent reactions
light harvesting complexes are part of ?
a photosystem
humans are ?
heterotophs
plants are ?
(photo)autotrophs
autotrophs are?
- can synthesise complex organic molecules from simple substances in their surroundings
- using energy from light or inorganic chemical reactions
- can ‘fix’ carbon
how do autotrophs fix carbon?
• inorganic form (CO2) ➡ organic (proteins, carbs, lipids)
heterotrophs?
cannot fix carbon, have to obtain C from complex organic molecules in other organisms, consuming them
autotrophs convert light energy into
chemical energy
Phys eq?
6CO2 + 6H2O ➡ (light energy) C6H12O6 + 6O2
resp eq?
C6H12O6 + 6O2 ➡ (ATP coming off arrow) 6CO2 + 6H2O
Another type of autotroph?
- chemoautotroph
* obtain light energy from chemicals
leaves must be able to?
- contain chlorophyll and other photosynthetic pigments
- take out O2 and in CO2
- steady water supply
- make carbs and transport them
what is the reaction centre pigment molecule?
chlorophyll a - 2 types though
2 sets of reactions in phys?
- light dependent
2. light independent
LDR can only occur if?
pigments that can absorb certain wavelengths of light are present
why is light needed in LDRs?
- photolysis - splitting H2O ➡ H2 + O
* provide chemical energy (ATP) for the reduction of CO2 to C6H12O6 in LID
What are photosynthetic pigments?
- coloured molecules that absorb specific wavelengths of light (colours)
- pick up specific colours not others
what happens to the wavelengths of light that are not absorbed?
- wavelengths not absorbed are either reflected or transmitted through
- we only see unabsorbed wavelengths
2 major photosynthetic pigments in plants?
- chlorophyll a
- chlorophyll b
- chlorophyll a absorbs slightly longer wavelengths of light than b
- this can be plotted on a graph called an absorption spectrum
In all photosynthesising plants there is?
chlorophyll a
accessory pigments?
- e.g. carotenoids (carotene) which absorb more blue/ green light than chl
- accessory bc there to help chl
- pick up wavelengths of light that would otherwise be missed and pass the energy onto chl
% error equation?
uncertainty / measurement x100
x2 if 2 measurements taken
to get total % error?
add them together
to decrease percentage error?
- use longer TLC paper
* take photo and zoom in ➡more accurate measurement ➡ reduced uncertainty
uncertainty is ?
half of resolution
chloroplast structure?
- lamella
- starch grain
- envelope
- DNA loop
- lipid droplet
- 70s ribosomes
- thylakoid
- granum
- stroma
lamella?
paired membranes (the disks in the cell)
granum?
• flattened stack of thylakoids
- hold pigments and enzymes for phys
- increase SA:V for max light absorption
- site of chemiosmosis
- grana = plural
thylakoid?
membrane bound sac studded w phys pigments & e-s carriers
stroma?
- would be cytoplasm if was cell
* 2 phospholipid membrane system runs thru the stroma - this is the site of LDRs
size and shape of chloroplast?
- biconcave disk
* 3-10 micrometer
2 variations of the reaction centre (chl a )
• P700
• P680
refers to wavelength of light best absorbed
access pigms are pigments other than ?
chl a
LDR summary?
H2O (+light energy) ➡ O2
takes place in the thylakoid membrane
LDR and LID reactions are linked by?
ADP reversible arrow ATP
OxNADP to redNADP and back
LID reaction summary?
CO2 ➡ Calvin cycle ➡ glucose
stroma
NADP?
- coenzyme
* acts as hydrogen carrier
The Z scheme?
- H2O -> H2 +O2 - splitting = photolysis
- ATP produced in photophosphorylation
- and redNADP
- ATP and redNADP passed onto the LID stages
How is redNADP formed?
- red= gain of e-
- H2O -> 2H+ + 2e- + 1/2O2
Photophosphorylation?
- ADP -> ATP
- can be cyclic or non cyclic
- 1 photosystem involved
Cyclic photophosphorylation?
- generates ATP but not redNADP
- photons passed on by acc. pigments to P700
- an e- in the chl a is excited to a higher energy level and is emitted from the chl a
- picked up by an e- carrier
- passed back to P700 via a chain of e- carriers
- As it is passed along, enough energy is released to phosphorylate ADP
only ? is involved in CP?
PS1
non-cyclic photophosphorylation?
- e-s emitted and move to P700
- now P680 has a + charge
- light absorbed by both photosystems
- excited e-s are emitted by both PS
- both now have + charge
- At PSII e- picked up by e- acceptor
- passed along by e- carriers where it is absorbed by PSII reaction centre
- as the e- are passed along, enough energy is released to ADP-> ATP
non-cyclic photophosphorylation 2
- e- in PSII are replaced by the photolysis of H2O
- PSII has a H2O splitting enzyme
- H2O -> 2H+ + 2e- + 1/2O2
- H+ combine with e- from PSI and NADP to give NADPH2 (redNADP)
both NADP and ATP pass onto LIR to make glucose
⭐ cannot make redNADP using…
cyclic phosphorylation
ATP synthase is a.k.a as
ATPase
how does photophosphorylation work?
- using chemiosmosis
Chemiosmosis?
- movement of high energy e- down ETC
- energy from e- used to AT H+ across thylakoid membrane
- formation of H+ gradient
- Facilitated diffusion of H+ through ATP synthase
- production of ATP using energy from the movement of H+
- for every 3H+ that go through, 1 ATP made
LIR?
Calvin Cycle
LIR background?
- occurs in the stroma
- takes place regardless of whether light is present or not
- basically the reduction of CO2 using redNADP and ATP from LD
How many turns of the calvin cycle are needed to make a hexose sugar?
- 1 C entered every turn
- so 6 turns needed
calvin cycle fixes
C
stages of Calvin Cycle?
- CO2 combines with RuBP (5C) forming ustable 6C intermediate
- intermediate breaks up into 2 mols of GP (3C)
- GP + redNADP + ATP -> TP (+Pi, ADP, oxNADP)
- some TP converted through a sugar shuffle into RuBP
- some released from cycle to condense, some makes hexose sugars, some converted to acetyl coA
RuBISCO is the enzyme that?
converts RuBP + CO2 into 2GP
Factors affecting rate of phys?
- light intensity
- CO2 conc
- Temp
limiting factor?
- factor that is in the shortest supply
- if another factor increases, no difference because the limiting factor is the one that is actually affecting the rate of phys
whichever factor is the most limiting is
in the shortest supply and and is the limiting factor
Why is temp imp for LIDs?
- KE needed for enzymes (Rubisco)
When you increase the limiting factor, why does the graph eventually plateau off?
another factor becomes limiting
CO2 conc in air?
0.04%
Q10 ?
- should be 2 for biological systems
- but is not for LDRs as not controlled by enzymes
Why is temp more complicated as a LF?
- LDRs not directly affected by temp bc they’re noy enzyme catalysed reactions that occur in solution like LIR. So Q10 not around 2
- At higher T and lower CO2 conc, O2 can act as a competitive inhibitor for rubisco, slows the rate of phys
LF: water stress?
- when water in short supply, stomata close to reduce water loss
- CO2 entry decreases so the rate of LIR decreases
- water availability is not considered a LF bc for water to become limiting, water potential of the cells will have become so low that stomata will have already closed stopping phys
light intensity and distance are ?
- inverse square law
- LI = 1/d^2
- the light intensity becomes 1/4 when distance x2
problems with LI PAG?
- determining colour = subjective ➡ use colorimeter
- only did once = repeatability unclear
- light from other lamps - true LI is different
- diff sizes = diff SA = less diffusion distance
where do autotrophs get CO2 ?
- air, respiration of heterotrophs
- H2O: respiration of plant cells, from soil
where does glucose go from autotrophs?
- resp
- biosynthesis of other molecules by plant cells which can be used as a food source by heterotrophs
where does O2 go from autotrophs?
- resp of plant cells
- excreted into atmosphere if in excess, can be used for resp by heterotrophs
where does glucose come from for resp of autotrophs?
- phys
- or storage molecules e.g. starch
where does O2 come from for resp of autotrophs?
phys or atmosphere
where does CO2 go from autotrophs in resp?
- air, via stomata
- used in phys
where does water go from autotrophs in resp?
air as water vapour or phys
where do heterotrophs get glucose from for resp?
- eating food
- storage molecules like glycogen in muscle and liver tissue
where do heterotrophs O2 from for resp?
air
how do heterotrophs get rid of CO2?
air
how do heterotrophs get rid of H2O?
urine (Excreted) or enters cell’s cytoplasm, TF, blood
the long thing on diagrams between grana is?
lamella
CP only involves ?
PS1 not PSII
Lollipop experiment aim?
- to discover the order of compounds synthesised after CO2 is fixed
What was the lollipop?
a thin flask containing algae - apparatus looked like a lollipop
Lollipop experiment: how was C14 used?
- algae were exposed to C14O for short lengths of time
- this fixed the C14 onto more compounds, the longer the exposure
- C14 is radioactive so shows up on chromatograph - location can be detected
Lollipop experiment: why was ethanol boiled?
kill algae to stop them phys
Lollipop experiment: how were the compounds separated from the algae?
2D chromatography: w 2 diff solvents
Lollipop experiment: how were the compounds containing C14 identified?
- used autoradiography
- where compounds containing C14 appeared as dark smudges
in the membrane of the thylakoid,
LDR happening
Why are thylakoids stacked into grana?
- inc SA of the membrane containing proteins needed for LDRs
- more membrane = more proteins = more LDRs
compensation point on LF graph?
• part where the line crosses the x axis
resp rate = phys rate
at very low LI
- graph goes below x axis for CO2 uptake
* resp> phys rate so CO2 being produced not used
Why is keeping a greenhouse warm in the winter a bad idea?
LI is the LF not temp so it would be a waste of energy and plant may start respiring more, the plant would be using up the fuel more than it was making it
Q10 equation?
Q10 = R2/ R1 (^10/ temp change)
R1 and R2?
R1 = rate before the temp rise R2 = rate after T rise
What happens to [TP], [GP] and [RuBP] in high LI conditions?
- At high LI, ATP and redNAD are in plentiful supply from the LDRs
- so all conversions can happen at an equal rate
- so levels remain constant
What happens to [TP] in low LI?
- needs ATP and redNAD from LDR which are not occuring
* so levels fall
What happens to [RuBP] in low LI?
- At low LI, ATP and redNADP are now not being provided by the LDR
- GP to TP slows and stops
- but TP to AA and lipids continues
- tp TO RuBP stops so levels decline
What happens to [GP] in low LI?
• RuBP -> GP continues so GP levels rise
When LI rises again?
- ATP and redNADP available again
- GP to TP can happen again so GP levels fall back down and TP levels rise
- TP to RuBP can happen again to RuBP levels rise
at low LI the conc of only ? rises
GP
TP can also go on to make?
hexose sugar
