Photosynthesis Flashcards
compare photosynthesis + aerobic respiration + anaerobic respiration
where it occurs
energy
conversion of energy
anabolic or catabolic
overall equation
how ATP is produced
coenzyme used
describe how ATP is synthesised
electrons excited
pass through electron transport train
energy released
+ used to pump protons across membrane
creates conc gradient
protons diffuse back through membrane down conc - CHEMIOSMOSIS
diffuse via hydrophilic transmembrane channels linked to ATP synthase
flow of protons provide energy needed to make ATP from ADP + Pi
what is chemiosmosis
Diffusion of protons from region of high concentration to region of low concentration
what does chemiosmosis result in
Movement of protons down gradient released energy used in attaching phosphate ion to ADP forming ATP
how are electrons excited
Electrons present in pigment molecules – chlorophyll – are excited by absorbing light
High energy electrons released when chemical bonds are broken in respiratory substrate molecules
what is the electron transport chain
Made up of electron carriers – progressively lower energy levels
how large are chloroplasts
2 – 10 micrometres in diameter
larger than mitochondria
describe the structure of chloroplasts
Surrounded by double membrane
Have cytosol-like fluid – stroma
Has separate system of membranes
describe the double membrane
Outer – permeable to ions / small molecules
Inner – has transport proteins
what is in the stroma
Carbon dioxide / sugars / enzymes
Has 70s ribosomes + loop of DNA + starch grains
describe the separate membrane system
has flattened fluid-filled sacks = thylakoids
Thylakoid membrane – has pigments / enzymes / electron carriers
Thylakoids stack to form grana
Grana connected by membranous channels – lamellae
what is the purpose of lamellae
Ensure sacs are connected but distanced from each other
Membrane of grana – large SA
how is the stroma adapted for photosynthesis
Gel-like fluid
Enzymes for light-independent reactions
Surrounds grana and membranes
Facilitates rapid transport of products from light-dependent stage
how is the grana adapted to photosynthesis
Stacks of thylakoids
Large surface area
Presence of many photosystems
Maximizes light absorption
More membrane space for electron carriers and ATP synthase enzymes
how are the ribosomes adapted for photosynthesis
Present in chloroplast
Allows translation of proteins coded by cpDNA
how is the inner membrane adapted for photosynthesis
Selective transport proteins
Control flow of molecules between stroma and cytosol
what are the two types of pigments
chlorophylls
carotenoids
what are the two types of chlorophyll
chlorophyll a
chlorophyll b
what are the two types of carotenoids
beta carotene
xanthophyll
what are the colours of the chlorophyll pigments
chlorophyll a - yellow-green
chlorophyll b - blue-green
what are the colours of the carotenoids pigments
beta carotene - orange
xanthophyll - yellow
what wavelengths do chlorophyll absorb + reflect
absorb wavelengths in blue-violet + red regions
reflect green light
what wavelengths do carotenoids absorb
absorb wavelength’s in blue-violet regions
what is a photosystem
??
Light harvesting system + reaction centre
what is the role of a photosystem
to absorb / harvest light energy + transfer energy quickly to reaction centre
where are the photosystems found
In the membrane of thylakoids
what are the two photosystems
Photosystem 1 (P700)
Photosystem 2 (P680)
what is the max absorption of photosystem 1
700nm
what is the max absorption of photosystem 2
680nm
what are the two stages of photosynthesis
light dependant
light independant - calvin cycle
what happens overall in the light dependant stage
Energy from sunlight absorbed + used to form ATP
Hydrogen from water used to reduce coenzyme NADP to reduced NADP
where does the light dependant stage occur
Thylakoid membrane
what process does the light dependant stage occur via
noncyclic or cyclic photophosphorylation
describe non cyclic photophosphorylation
Light absorbed by PS2
PS2 has oxygen evolving complex – water splitting enzyme
Breaks down water - photolysis = H2O → 2H+ + 2e- + ½O2
Photon collides with chlorophyll a + excites an electron in a Mg atom (photoionisation)
As electrons leave PS2 – replaced by electrons from photolysis
excited electrons pass down electron transport chain
H+ transported to stroma by ATP synthase
Chemiosmosis + photophosphorylation
Electron passes from electron transfer chain to PS1
Electrons excited at PS1 in Mg atom - photoionisation
New electron goes through electron carrier 2
+ replaced by electron coming from electron carrier 1 (PS2)
Electrons combine with H+ and NADP to get reduced NADP (NADPH
describe chemiosmosis again
As high energy electrons move through carriers – energy released
Energy used to pump protons across membrane from stroma to thylakoid lumen= making conc gradient
Gradient maintained from permeability of membrane to hydrogen ions
NOW - only way protons move back through membrane DOWN conc gradient is through membrane channels linked to ATP synthase
Facilitated diffusion of protons provides energy used to make ATP from ADP + Pi
what are the end products of non cyclic photophosphorylation
Used water
Produced oxygen as a biproduct
Produced NADPH + ATP
describe cyclic photophosphorylation
Only involves PS1
Times of stress
Rather than end result of NADPH – electron passed back to PS2 from PS1
Re-enters electron transfer chain
Keep pumping H+ into thylakoids = produce more ATP
NO reduced NADPH produced
state the difference between cyclic + non cyclic photophosphorylation
?
where does the light independant stage occur
stroma
describe the calvin cycle
Carbon dioxide enters intercellular spaces in spongy mesophyll via diffusion through stomata
Diffuses into stroma of chloroplasts
Combined with ribulose biphosphate (RuBP)
Carbon dioxide is now fixed – incorporated into organic molecule
Six carbon unstable intermediate produced
Breaks down – 2 three carbon glycerate 3-phosphate (GP) molecules
Each GP reduced into another 3 carbon – triose phosphate (TP)
Uses hydrogen from NADPH + energy from ATP
TP – carbohydrate + majority recycled to regenerate RuBP
Regeneration uses ATP
draw out the calvin cycle
what is the fixation of carbon dioxide
Combining with ribulose biphosphate (RuBP
what is RuBP
5 carbon sugar
ribulose biphosphate
what is the fixation of carbon dioxide catalysed by
Catalysed by ribulose biphosphate carboxylase (RuBisCO)
whats bad aboutn RuBisCo
Carbon dioxide is now fixed – incorporated into organic molecule
what needs to happen in the calvin cycle for 1 glucose molecule to be made
six carbon dioxide molecules have to enter
6 full turns of the cycle
make 12 TP molecules – 2 of which will be removed to make the glucose molecule
10 TP molecules recycled to make 6 RuBP
what are the uses of TP
Can condense to form hexose phosphate – used to produce starch / sucrose / cellulose
Can be converted into glycerol
Used to make amino acids
state the factors effecting rate of photosynthesis
light intensity
carbon dioxide conc
temperature
how does light intensity effect rate of photosynthesis
Rate of photosynthesis increases as light intensity increases
Greater light more energy supplied to plant
Faster light dependant stage can occur
Produces more ATP + NADH for Calvin cycle
state the relationship between decreasing light intensity and the conc of NADH / GP / TP / RuBP
Decrease light intensity = decreases conc of TP + RuBP
BUT slight increase in GP
how does decreasing light intensity effect conc of NADH / GP / TP / RuBP
Decrease light intensity = decrease in TP + RuBP BUT slight increase in GP
Less light – light dependant stops + doesn’t form any more products (ATP + NADH)
GP builds up as it is not converted to TP
Lack of TP – RuBP wont form
Overtime fixation of carbon dioxide will stop + GP conc will plateau
how does carbon dioxide conc increase rate of photosynthesis
rate of photosynthesis increases as carbon dioxide concentration increases
More carbon dioxide.. more combined with RuBP + faster
Faster Calvin cycle + faster rate of photosynthesis
state the relationship between decreasing carbon dioxide conc and the conc of NADH / GP / TP / RuBP
Low conc of carbon dioxide – decrease in conc of GP + TP but increase in RuBP
how does decreasing carbon dioxide conc effect conc of NADH / GP / TP / RuBP
Low conc of carbon dioxide – decrease in conc of GP + TP but increase in RuBP
RuBP accepts carbon dioxide so when there is a lack it remains unfixed + builds up
Prevents TP + GP from forming
why doesnt temp have a significant effect on the light dependant stage
driven by light energy rather than kinetic energy
how does increasing temp effect rate of photosynthesis
Increasing temp – cause stomata to close – carbon dioxide cant be fixed + slow rate down
Light dependant reaction relied on proton gradient forming across thylakoid membrane = membrane permeability influenced by extreme temp
