photosynthesis Flashcards
relationship between the process of photosynthesis and respiration-
biological processes need energy
example of plants and animals:
without energy, what would happen to these biological processes?
-plants= need energy for photosynthesis, active transport, DNA replication, cell division and protein synthesis.
-animals= need energy for muscle contraction, maintenance of body temp, active transport, DNA replication, cell division and protein synthesis
-they would stop and the plant or animal would die.
what does photosynthesis store energy in?
what is the equation of photosynthesis?
animals cant eat their own food so?
-glucose, plants make their own food (glucose) using photosynthesis. The energy is stored in glucose until the plants release it by respiration.
- 6CO2 + 6H2O + energy —> C6H12O6 (glucose) + 6O2
-they obtain glucose by eating plants (or other animals), then respire the glucose to release energy.
what is respiration?
what are the two types of respiration?
respiration equation?
-when living cells release energy from glucose
-Aerobic respiration= respiration using oxygen
-Anaerobic respiration= respiration without oxygen
-C6H12O6 (glucose) + 6O2 —> 6CO2 + 6H2O + energy
relationship between photosynthesis and respiration-
what do they both involve?
how do they work?
what is the coenzyme used in photosynthesis?
what coenzymes are used in respiration?
what does photosynthesis make but respiration use?
-coenzymes
-by temporarily binding to the enzyme and transferring a chemical group from one molecule to the other
-NADP= it transfers hydrogen from one molecule to the other, meaning it can oxidise and reduce a molecule.
-NAD, coenzyme A and FAD
-NAD and FAD transfer hydrogen from one molecule to the other ( means they can reduce or oxidise a molecule)
- coenzyme A transfers acetate between molecules
-glucose
look at pic of chloroplast in folder
how are thylakoid stacks (fluid filled sacs) adapted to their function?
-contain photosystems/carotene pigments (named pigments)
-contain ATP synthase
-large surface area in a small volume for light absorption, light dependent reactions, light dependent stage, electron transport
what do chloroplasts contain?
what do photosynthetic pigments do?
what is the protein and pigment called?
why are there a range of accessory pigment sin photosystems?
what and the accessory pigments and what colour are they?
why do plants look green?
-photosynthetic pigments (eg chlorophyll a, chlorophyll b, carotene)
-coloured substances that absorb light energy needed for photosynthesis, and are found in thylakoid membranes and are attached to proteins.
-a photosystem
-to be able to absorb different light wavelengths
-chlorophyll a =blue/green
-chlorophyll b = yellow/green
-caratenoids =orange
-xanthophylls = yellow
-phaeophytins = grey
-because green light is reflected
a photosystem contains two types of photosynthetic pigment which are?
what are primary pigments?
what are accessory pigments?
-primary pigments and accessory pigments
-reaction centres, where electrons are excited during the light-dependent reaction (chlorophyll a)
-these make up the light harvesting system/complex. they surround reaction centres and transfer light energy to them to boost the energy available for electron excitement to take place
what are the two photosystems used by plants to capture light energy? and what wavelength do they absorb light best at?
-photosystem I (PSI) = absorbs light best at a wavelength of 700nm
-photosystem II (PSII) = absorbs light best at a wavelength of 680nm
what does the stroma contain?
-its a gel-like substance, and contains enzymes, sugars and organic acids
-it also contains the carbohydrates that are produced by photosynthesis that aren’t used right away, these are stored as starch grains in the stroma
-their own DNA and is found in the stroma and is often circular there can be multiple copies in each chloroplast
what are the two stages that make up photosynthesis?
-The light-dependent reaction
-The light-independent reaction
THE LIGHT-DEPENDENT REACTION-
what does this reaction need?
where does it take place?
what happens to light energy?
what is this light energy used for?
what does ATP do? and what does NADPH do?
during this process what happens to H2O?
-light energy
-in the thylakoid membranes of the chloroplast
-light energy is absorbed by photosynthetic pigments in the photosystems and is converted to chemical energy
-used for 3 things:
*Making ATP from ADP and inorganic phosphate- called phosphorylation
*making reduced NADP (NADPH) from NADP
*splitting water into protons (H+ ions), electrons (e-) and oxygen -called photolysis
-ATP transfers energy and reduced NADP (NADPH) transfers hydrogen to the light-independent reaction.
H2O is oxidised to O2
LIGHT-DEPENDENT REACTION-
how many types of phosphorylation does the light-dependent stage include?
-two types of phosphorylation= non-cyclic and cyclic
LIGHT-DEPENDENT STAGE: non-cyclic phosphorylation
what are photosystems linked by?
what do the photosystems and the electron carriers form?
-electron carriers, which are proteins that transfer electrons
-an electron transport chain = a chain of proteins that excited electrons flow through
(look at pics in folder) NON-CYCLIC PHOSPHORYLATION-
what happens after the light is absorbed in the light harvesting system?
-light energy excites electrons in chlorophyll light energy is absorbed by PSII
-the electrons move to a higher energy level
-the electrons then move along the electron transport chain to PSI
-as the excited electrons from chlorophyll leave PSII to move along the electron transport chain, they must be replaced
- so, light energy splits water into protons, electrons and oxygen. the reaction is: H2O —-> 2H+ + 1/2 O2.
- so, the electrons lost from PSII are replaced with those from the photolysis of water
- and the electrons lost from PSI are replaced with ones from PSII.
-the excited electrons lose energy as they move along the electron transport chain, this energy is used to transport protons into the thylakoid, via membrane proteins called proton pumps
-so that the thylakoid has a higher conc of protons than the stroma = forming a proton gradient across the membrane
-protons move down their concentration gradient, into the stroma, via an ATP synthase.
-The energy from this movement combines ADP and Pi to form ATP = called chemiosmosis
-light energy is absorbed by PSI, which excites the electrons again to an even higher energy level
-the electrons are then transferred to NADP, along with a proton from the stroma, to form reduced NADP (NADPH).
CYCLIC PHOSPHORYLATION-
what does cyclic phosphorylation use?
what is cyclic phosphorylation?
what does this mean?
what does this process NOT produce?
what DOES this process produce?
-only uses PSI photosystem (there is a light harvesting complex in both photosystems)
-called ‘cyclic’ because the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers.
-means the electrons are recycled and can repeatedly flow through PSI
-light energy is absorbed by PSI, which excites the electrons again to an even higher energy level
-the excited electron is captured by an electron acceptor transported by electron transport chain before being passed back to PS1
-as electrons pass through electron transport chain, they provide energy to transport protons from the stroma to the thylakoid lumen via proton pump
-a build up of protons in the thylakoid lumen then drives the synthesis of ATP from ADP + Pi by chemiosmosis
-photolysis does not occur and cyclic phosphorylation does NOT produce any reduced NADP or oxygen
-only produces small amounts of ATP
what are the products of the LIGHT-DEPENDENT stage?
-reduced NADP
-ATP
-oxygen
THE START OF THE LIGHT DEPENDENT STAGE-
The light harvesting system is found on the surface of the internal membranes of the chloroplast.
Describe how light is harvested in the chloroplast membranes?
-primary (chlorophyll a) and accessory pigments (carotene) form a photosystem
-light energy is absorbed by different pigment molecules
-electron is excited and is returned to pigment.
-energy is passed from one pigment to another
-accessory pigments pass energy to reaction centres which contains chlorophyll a
-the range of accessory pigments allow a range of wavelengths to be absorbed
-primary pigments pass electrons to ETC (electron transport chain)
LIGHT-INDEPENDENT REACTION- otherwise known as the Calvin cycle
where does it happen?
what is the Calvin cycle also known as?
what are the products of the LD stage that are used in the Calvin cycle of the LI stage?
-in the stroma of the chloroplasts
-carbon dioxide fixation because carbon from CO2 is ‘fixed’ into an organic molecule
-ATP and reduced NADP
what is the electron donor in both cyclic and non-cyclic stages?
what is the final electron acceptor in both cyclic and non-cyclic stages?
-electron donor:
cyclic = chlorophyll a in PSI
non-cyclic = PSII or the photolysis of water
final electron acceptor:
cyclic = chlorophyll a in PSI
non-cyclic = NADP
LI STAGE (CALVIN CYCLE)-
what happens in the Calvin cycle? (also look at pic in folder)
1) FIXATION STAGE
-CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast.
-Here, the CO2 combines with ribulose bisphosphate (RuBP) by the enzyme RUBISCO, RuBP is a 5-carbon compound.
-This gives and unstable intermediate 6-carbon compound which breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate (GP).
2) REDUCTION STAGE
-ATP (from LD reaction) provides energy to turn GP into a different 3-C compound called triose-phosphate (TP).
-requires H+ ions which come from reduced NADP (from LD reaction).
-reduced NADP is recycled to NADP (to be used in the LD reaction).
-TP is then converted into many useful organic compounds (and GP is too).
3) REGERNERATION STAGE
-5/6 molecules of TP produced in the Calvin cycle AREN’T used to make hexose sugars. They are used to regenerate RuBP.
-Regenerating RuBP uses the rest of the ATP produced by the LD reaction.
what are the organic compounds that GP and TP are converted into?
-carbohydrates = hexose sugars (glucose)are made by joining two TP molecules together. The larger carbohydrates (sucrose, starch, cellulose) are made by joining hexose sugars together in different ways.
-lipids = made using glycerol, which is synthesised from TP and fatty acids, which are synthesised from GP.
-amino acids = some amino acids are made from GP.
CALVIN CYCLE-
how many turns of the Calvin cycle are needed?
-Three turns of the cycle produces 6 molecules of TP, because 2 molecules of TP are made for every 1 CO2 molecule used.
-And 5/6 of these TP molecules are used to regenerate RuBP.
-so, for 3 turns of the cycle, only 1 TP molecule is produced that’s used to make a hexose sugar
-a hexose sugar has 6-carbons though, so two TP molecules are needed to form 1 hexose sugar
- 6 turns of the cycle need 18 ATP and 12 reduced NADP from the LD reaction.
what are the reactants of the Calvin cycle?
what are the products of the Calvin cycle?
-CO2
-reduced NADP
-ATP
-organic molecules eg. glucose
-oxidised NADP
HOW LIGHT, TEMP AND CO2 AFFECT THE LEVELS OF GP RuBP AND TP-
light intensity?
-in low light intensities, the products of the LD stage (reduced NADP and ATP) will be in short supply
-means that the conversion of GP to TP and RuBP is slow.
-so, the level of GP will rise (cos its still being made) and levels of TP and RuBP will fall (as they are used to make GP)
HOW LIGHT, TEMP AND CO2 AFFECT THE LEVELS OF GP RuBP AND TP-
temperature?
-all the reactions in the Calvin cycle are catalysed by enzymes (eg RuBisCO)
-at low temps, all of the reactions will be slower as the enzymes work more slowly.
-this means the levels of RuBP, GP and TP will fall
-GP, TP and RuBP are affected in the same way at very high temperatures, because the enzymes will start to denature
HOW LIGHT, TEMP AND CO2 AFFECT THE LEVELS OF GP RuBP AND TP-
carbon dioxide concentration?
-at low CO2 concs, conversion of RuBP to GP is also slow (as there’s less CO2 to combine with RuBP to make GP)
-so, the level of RuBP will rise (as its still being made) and the levels of GP and TP will fall (as they are being used up to make RuBP)
look at graphs of limiting factors-
how does water stress affect photosynthesis?
when plants down have enough water, their stomata will close to preserve what little water they do have, leading to less CO2 entering the leaf for the Calvin cycle and slowing photosynthesis down.
how can photosynthetic pigments be separated?
describe the steps?
-by using Thin Layer chromatography (TLC), this involves a mobile phase and a stationary phase
- grind up leaves (spinach) with some anhydrous sodium sulphate and some propanone
- transfer the liquid to a test tube, add some petroleum ether and gently shake the tube
what happens at high light intensity?
what happens to photosynthesis if temperature falls below 10°C?
if temp is more than 45°C
also at high temperatures what happens?
what happens if CO2 increases?
-the higher the intensity, the more energy it provides
-enzymes become inactive
-enzymes start to denature ( eg ATP synthase and rubisco)
- stomata close to avoid losing much water = slows down photosynthesis as less CO2 enters the leaf when the stomata are closed
- the thylakoid membranes may be damaged = could reduce the rate of the LD stage reactions by reducing the number of sites available for electron transfer
- the membranes around the chloroplasts could be damaged, which could cause enzymes important in the calvin cycle to be released into the cell = which would reduce the rate of the LI stage reactions
- chlorophyll could be damaged = this would reduce the amount of pigment that can absorb light energy = which would reduce the rate of the LD stage reactions
-CO2 makes up 0.04% of gases in atmosphere
-increasing this to 0.4% gives a higher rate of photosynthesis, BUT any higher would make stomata start to close
