Flashcards
Photosynthesis
Flashcards do conjunto (45)
- 1Overall equation for photosynthesis LOOK AT DIAGRAM P186CO2+6H2O---> C6H12O6+ 6CO2
2 photosynthesis stages- light dependent/ light independent stage
Light dependent- converts light energy to chemical- photolysis of water- releases electrons and protons- energy carried by electrons creates proton gradient across thylakoid membrane- energy used for photophosphorylation of ADP-endergonic reaction bonding phosphate ion to a molecule of ADP, using light energy, making ATP- protons and electrons reduce NADP- light independent- ATP and reduced NADP reduce CO2- produce energy containing glucose - 2Chloroplasts and light trappingPhotosynthesis happens in chloroplasts- surrounded by double membrane- folded inward to form thylakoid lamellae- combine in stacks- granum- groups grana- in grana is most of photosynthetic pigments for light dependent stage
Stroma= fluid filled interior- bathes thylakoids/ grana- where light independent reactions occur
If starch grains were present- would appear white as stain for electron micrographs binds to lipids not carbs - 3Where is chlorophyll foundonly in parts that are exposed to light- leaves, petioles and stem- leaf= main organ of photosynthesis- chloroplasts found in palisade mesophyll but also in spongy mesophyll- only epidermal cells containing chloroplasts= guard cells
- 4Structural features and significance for photosynthesis- ANGIOSPERM leafLarge SA- Capture as much light as possible
Thin- light penetrates right through leaf
Stomatal pores- allow CO2 to diffuse into leaf
Air spaces in spongy mesophyll- Allow CO2 to diffuse into photosynthesising cells
Spaces between palisade cells- Allow CO2 to diffuse to photosynthesising cells - 5Structural features and significance for photosynthesis- cellsCuticle and epidermis are transparent/ cellulose cell walls are thin= light penetrates straight through the mesophyll
palisade cells have a large vacuole- chloroplasts form a single layer at periphery (edge) of each cell- so do not shade each other
Palisade cells are cylindrical, elongated at right angles to the surface of the leaf-leaves can accomodate large no. palisade cells- light only passes through 2 epidermal cells and 1 palisade cell to reach chloroplast- if cells were stacked horizontally light would have to pass through many cell walls- won't reach chloroplast - 6Structural significance- chloroplastsLarge SA- max light absorption
Chloroplasts move within palisade cells- move toward top on dull days- for max light absorption- if light intensity = very high moves to bottom-prevent pigment bleaching
Chloroplasts rtate in palisade cells/
Pigments in thylakoids= in single layer at surface of thylakoid membrane-max absoption
5x as many chloroplasts in palisade than spongy mesophyll cells- palisade= top of leaf- exposed to more light- so max light absorption - 7Diagramp20
- 8Chloroplasts as transducersbio transducers- more efficient than artificial- waste less energy- chloroplast= transducer- turns energy from photons of light to chemical energy- made available through ATP- incorporated into molecules eg glucose
- 9Englemann's expUsed filamentous green algae- determined which wavelengths of light were most effective- put algae in suspension of evenly distributed, motile aerobic bacteria - exposed to range of wavelengths- blue and red light- bacteria clustered near chloroplasts- deduced wavelengths resulted in high photosynthesis- where there was most O2- bacteria flocked to
- 10Photosynthetic pigmentsPigment= molecule that absorbs specific wavelengths of light- different photosynthetic pigments trapping different wavelengths- large range absorbed- more useful- 2 main classes of pigments= transducers- chlorophylls/ carotenoids
- 11Chlorophyllschlorophyll a- peak wavelengths- 435,670-680= blue-green- in all (mosses, ferns, conifers, flowering plants)
chlorophyll b- peak wavelength- 480, 650- yellow- green - higher plants (conifers, flowering plants) - 12CarotenoidsB (beta)- carotene- 425-489- orange- all
xanthophylls- 400- 500- yellow- most - 13Absorption and action spectraAbsorption spectrum- graph showing how much light is absorbed at different wavelengths
Action spectrum- graph showing rate of photosynthesis at different wavelengths
different pigments absorb different wavelengths- seen by making seperate solutions of pigment- shining light through- chlorophylls a/b - absorb mainly at red/ blue/violet- reflect green- gives leaves colour
carotenoids- absorb blue/ green, reflect longer wavelengths- leaves appear orange - 14action spectrum moreshows rate of photosynthesis at different wavelengths measured by mass of carbs synthesised by plants exposed at different wavelengths
If action spectrum is superimposed on absorption spectrum- close correlation can be seen- suggests pigments responsible for absorbing light= used in photosynthesis - 15ton of diagramsp22
- 16What's in photosystems P1Antenna complex- contains photosynthetic pigments- chlorophylls/ carotenoids anchored in phospholipids in thylakoid membrane- held together by clusters of protein molecules= antenna complex- combo of pigments- range of wavelengths absorbed
- 17What's in photosystems P2Reaction centre- within antenna complex- contains 2 molecules of primary pigment chlorophyll a - when molecules absorb light- excitation causes both to release 1 electron- 2 types of reaction centre-
Photosystem 1- arranged around 2 chlorophyll molecules - absorption peak of 700nm
Photosystem 2- named last but comes first- arranged around 2 chlorophyll molecules absorption peak of 680nm - 18What's in photosystems P3Some photons absorbed by chlorophyll directly- but many absorbed first by accessory (antenna) pigments- photons excite these pigments- energy passed on to reaction centre- electrons of chlorophyll get excited/ raised to higher energy level-chlorophyll a= most significant molecule of reaction centre- passes energy to subsequent reactions f photosynthesis
- 192 stages of photosynthesisPhotosynthesis= sequence of reactions- takes place in thylakoid membranes -
Light dependent reactions occur in the thylakoid membranes and thylakoid cavity and require light energy and water. Light energy is transformed to chemical energy in ATP and NADPH (oxygen as a by-product of photosynthesis).
The light independent reactions (Calvin cycle) occur in the stroma. They consume CO2 and energy from ATP and reduced NADP and organic chemicals e.g. carbohydrates are produced. - 20Light dependent stage- photophosphorylationPhotosynthesis has 2 pathways of photophosphorylation- non cyclic- includes both PSI and PSII- in linear direction- cyclic= includes only PSI- excited electrons from PS I can pass from the electron acceptor to the electron carriers and back, via the proton pump, to PS I.
- 21Cyclic photophosphorylationLight is absorbed by photosystem I -passed to the photosystem I primary pigment (P700)
An electron in the chlorophyll a is excited to a higher energy level and is emitted in a process known as photoactivation
This excited electron is captured by an electron acceptor, transported via a chain of electron carriers known as an electron transport chain before being passed back to the chlorophyll molecule in photosystem I (hence: cyclic)
As electrons pass through the electron transport chain they provide energy to transport protons (H+) from the stroma to the thylakoid lumen via a proton pump
A build-up of protons in the thylakoid lumen can then be used to drive the synthesis of ATP from ADP and an inorganic phosphate group (Pi) by the process of chemiosmosis
The ATP then passes to the light-independent reactions - 22Non cyclicphotons of light energy are absorbed by a pigment molecule of the antenna
complex of PS II; the excitation is passed to the pair of chlorophyll a molecules
in the reaction centre;
• each has one of their many electrons boosted from their ground state, to an
excited state;
• the excited electrons pass to electron acceptors, reducing them, leaving the
chlorophyll a molecules oxidised, they then pass via a series of electron
carriers;
• electron transfer is linked to proton pumping (via one proton pump) from the
stroma into the thylakoid space, raising its proton concentration and lowering
the pH;
• protons then flow down their gradient, through ATP synthetase, releasing
energy to form ATP; - 23Non cyclic p2- look at diagram p24photons of light energy are absorbed by a pigment molecule of the antenna
complex of PS I and the energy is passed to the pair of chlorophyll a
molecules in the reaction centre;
• each has one of their many electrons boosted from their ground state, to an
excited state;
• the excited electrons can each reduce an electron acceptor, which pass an
electron to oxidised NADP, reducing it. Each NADP receives two electrons
and picks up two hydrogen ions from the stroma to become reduced NADP
(NADPH + H+). - 24Photolysis of watermolecules of water within thylakoid spaces are split into hydrogen ions,
electrons, oxygen and reformed water;
• the electrons are removed to replace those lost by the chlorophyll a of
photosystem II;
• light is responsible only indirectly for splitting water.
photolysis- enhanced by protein complex in PSII- only known enzyme to oxidise water
electrons from PSI reduce NADP- O2 diffuses out of chloroplast into intercellular airspaces then out via stomata as waste product - 25Passage of protons and photophosphorylationelectrons pass through proton pump of thylakoid membrane- H+ ions join protons from water accumulate- builds electrochemical gradient between thylakoid membrane and stroma-chemiosmosis happens- down ATP synthase back to stroma- releases energy- phosphorylate ADP
Once in stroma H+ ions passed to oxidising NADP- reducing it NADP+2H+ + e-----> reduced NADP - 26Light dependent- equation and comparisonElectron flow- cyclic, non cyclic
chlorophyll at reaction centre- P700, P680
ATP production- yes, yes
Photolysis of water- no, yes
O2 production- no, yes
NADP production- no, yes
Occurrence- all photosynthetic organisms, plants/ algae/cyanobacteria - 27Light independent stage of photosynthesisOccurs in solution in stroma of chloroplast- involves many reactions - each catalysed by a different enzyme- used products of light dependent- ATP= source of energy- reduced NADP= source of reducing power- reduces CO2
- 28Light independent- calvins cycle5 carbon acceptor molecule- ribulose biphosphate (RUBP)- uptakes CO2- catalysed by ribose biphosphate carboxylase (rubisco) - unstable 6 carbon compound formed- immediately splits into 2 glycerate 3 phosphate molecules- -
- 29Light independent p2ATP ( for energy) and reduced NADP (for reducing powers) utilised from the light dependent reactions to reduce glycerate-3- phosphate to the 3C carbohydrate, triose
phosphate- NADP reformed-
converted to glucose phosphate then to starch by condensation- most of triose phosphate- goes through series of reactions- regenerates RuBP - cycle continues- ATP from light dependent stage used for this - 30Product synthesisPhotosynthetic molecules can make all the molecules they need- like animals ned fats, carbs and proteins- can be made by 3C carbons produced by carbon cycle- manufactured from triose phosphate
- 31Product= carbsCarbs- first hexose made from fructose bisphosphate- can be converted to glucose and combined w/ fructose to make sucrose for transport around plant- a glucose molecules may be converted to starch for storage or to B glucose which is polymerised into cellulose for cell walls
- 32Product= fats-acetyl co-enzyme A can be synthesized from glycerate 3 phosphate- made in calvin cycle - converted to fatty acids- triose phosphate can be converted directly to glycerol- fatty acids and glycerol undergo condensation reactions to form triglycerides
- 33Product- proteinsglycerate 3 phosphate can also be converted into amino acids for protein synthesis - amino group derived from NH4+ ions made from nitrate ions- (NO3-)- taken in at roots- transported through plant
- 34Limiting factors in photosynthesisPlants need suitable environment to be efficient at photosynthesis:
Reactants= CO2, water
Light at high enough intensity and suitable wavelengths
Suitable temp
If any is lacking= no photosynthesis- each factor has optimum- rate of photosynthesis is highest- if any is sub-optimal- rate= reduced- limiting factor- if factor increases- rate increases - 35CO2 concentrationCO2 conc increases from 0- rate of light independent reactions and therefore photosynthesis increases= limiting factor- yet above 0.5% rate of photosynthesis remains constant- CO2 not affecting rate- no longer limiting- rate decreases above 1%- stomata close- prevent CO2 entering-
rate of slowest reaction in a sequence determines overall rate of process (rate limiting step)- in light independent- reaction catalysed by rubisco= step - 36CO2 conc p2CO2= usually a limiting factor for terrestrial plants- 0.04% CO2 in air- crop plants most efficient at around 0.1%, Aquatic plants and algae get CO2 from hydrogen carbonate ion HCO3- , some algae can increase their concs with carbonic anhydrase- so it's not a limiting factor- optimum conc for algae is approx 0.1 mol dm-3
- 37Light intensityLight intensity= controls rate of photosynthesis - if plant= in darkness- light independent can still happen but light dependent can't- no oxygen produced
LIght intensity increases- light dependent= more efficient- overall rate of photosynthesis increases- light intensity controlling rate= limiting factor
10,000 lux light dependent at max rate- increasing intensity doesn't produce faster reactions- not limiting- even higher intensity- photosynthetic pigments= damaged- light dependent fails - 38Sun and shade plantsPlants have different adaptations for different light intensities- sun plants most efficient at photosynthesis for photosynthesis- shade plants most efficient at low light intensities
- 39Light compensation pointThe light intensity at which plant has no net gas exchange- volume of gases used and produced in respiration and photosynthesis are equal-photosynthesis can be assessed on CO2 uptake- rate of light dependent and consequently independent decreases- rate of CO2 uptake decreases- reaches point respiration provides all CO2 for photosynthesis and photosynthesis provides all O2 for respiration- no net gas exchange- LCP- occurs at lower light intensity for shade plants
- 40Temp/ waterIncreased temp- increased photosynthesis rate- kinetic energy of molecules increases in reactions- Above certain temp (optimum) enzymes progressively denature- rate decreases- temp= limiting
Scarce water- plant cells plasmolyse- stomata close- wilting happens - experiments w/ water deficient plants- slight water deprivation can reduce carbs made= limiting but as so many systems affected hard to see its affect on photosynthesis alone - 41Limiting factors can combineSometimes plant has optimal values for all environmental factors- then photosynthesis will occur efficiently and grow well- but if plant has several of these factors limiting eg temp/ light intensity= low- photosynthesis= reduced grow slowly - rate is controlled by factor closest to its minimum value
- 42Minerals nutritionInorganic nutrients needed may be limiting factors for metabolism- have various roles:
Structural eg calcium in middle lamella walls
Synthesis of compounds needed for plant growth- eg enzyme activators such as magnesium required by ATPase and DNA polymerase
May form an integral part of magnesium in chlorophyll iron in carriers of electron transport chain and manganese in photosystem II
Macronutrients include nitrogen, potassium, sodium, magnesium, calcium, nitrate and phosphate- required in greater quantities than micronutrients eg maganese and copper. - 43NitrogenMost of nitrogen in soil is in humus, in organic molecules of decaying organisms- inorganic nitrogen occurs as ammonium ions NH4+ or nitrate ions NO3- nitrogen is largely taken up by roots as nitrates but rhizobium in root nodules delivers ammonium ions to the plant- ions transported to the xylem- delivered to cells- ions are transported in the xylem and delivered to cells - nitrogen converted to ammonium ions which becomes amino( -NH2) groups of amino acids- amino acids= transported into phloem used for synthesis of proteins, chlorophylls and nucleotides
- 44Because of nitrogens role in protein and nucleic acid synthesis...symptoms of nitrogen deficiency causes reduced growth in whole of plant- nitrogen is also a component of chlorophyll and so deficiency causes chlorosis- yellowing of leaves due to inadequate chlorophyll production- chlorosis first appears in older leaves
- 45Magnesiumabsorbed as Mg 2+ - transported in xylem - required by all tissues but especially leaves- required by all tissues but especially leaves- Mg forms part of chlorophyll molecule so main symptom of Mg deficiency= chlorosis- begins in veins of older leaves as existing Mg in plant is mobilised and transported to newly formed leaves- Mg ions are also activators such as for ATPase