Topic 5A - Photosynthesis and respiration ARN * Flashcards
Photosynthesis, respiration and ATP photosynthesis limiting factors in photosynthesis Photosynthesis experiments respiration aerobic respiration respiration experiments
what do plants need energy for?
photosynthesis active transport - to take in minerals via their roots DNA replication cell division protein synthesis
what do animals need energy for?
muscle contraction maintenance of body temperature active transport DNA replication cell division protein synthesis
what is photosynthesis?
the process where energy from light is used to make glucose from H2O and CO2
(the light energy is converted to chemical energy in the form of glucose)
what is the overall equation for photosynthesis?
6CO2 + 6H2O + energy –> C6H12O6 + 6O2
how do animals obtain glucose?
by eating plants (or other animals) then respire the glucose to release energy
what happens to energy respiration?
plant and animal cells release energy from glucose.
this energy is used to power all the biological processes in a cell
what are the 2 types of respiration?
aerobic respiration - using oxygen
anaerobic respiration - without oxygen
what is the overall equation for aerobic respiration?
C6H12O6 + 6O2 –> 6CO2 + 6H2O + energy
what does anaerobic respiration produce?
in plants and yeast - produces ethanol and carbon dioxide and releases energy.
in humans - produces lactate and releases energy
how does a cell get energy from glucose?
the energy released from glucose is used to make ATP
ATP carries energy around the cell to where it’s needed via diffusion
how is ATP made?
it’s synthesised via a condensation reaction between ADP and inorganic phosphate using energy from an energy releasing reaction e.g. respiration
the energy is stored as chemical energy in the phosphate bond. the enzyme ATP synthase catalyses this reaction
What happens to ATP once it diffuses to where it is needed?
it’s hydrolysed back into ADP and inorganic phosphate. chemical energy is released from the phosphate bond and used by the cell. ATP hydrolase catalyses this reaction.
the ADP and inorganic phosphate are recycled and the process starts again
what specific properties does ATP have that makes it a good energy source?
stores or releases small, manageable amounts of energy small, soluble molecule easily broken down quickly re-made make other molecules more reactive can't pass out of the cell
how does ATP storing or releasing small amounts of energy make it a good energy source?
no energy is wasted as heat
how does ATP being small and soluble make it a good energy source?
it can be easily transported around the cell
how does ATP being easily broken down make it a good energy source?
energy can be easily released instantaneously
how can ATP make other molecules more reactive?
by transferring one of its phosphate groups to the molecule (phosphorylation)
how does ATP not being able to pass out of the cell make it a good energy source?
the cell always has an immediate supply of energy
what is a metabolic pathway?
a series of small reactions controlled by enzymes e.g. respiration and photosynthesis
what is phosphorylation?
adding phosphate to a molecule e.g. ADP is phosphorylated to ATP
what is photophosphorylation?
adding phosphate to a molecule using light
what is photolysis?
the splitting (lysis) of a molecule using light (photo) energy
what is photoioisation?
when light energy ‘excites’ electrons in an atom or molecule, giving them more energy and causing them to be released. the release of electrons causes the atom or molecule to become a positively-charged ion.
what is hydrolysis?
the splitting (lysis) of a molecule using water (hydro)
what is decarboxylation?
the removal of carbon dioxide from a molecule
what is dehydrogenation?
the removal of hydrogen from a molecule
what are REDOX reactions?
reactions that involve oxidation and reduction.
oxidation of one molecule always involves reduction of another molecule
what is reduction?
if something is reduced it has gained electrons and may have gained hydrogen or lost oxygen
what is oxidation?
if something is oxidised it has lost electrons, and may have lost hydrogen or gained oxygen
what is a coenzyme?
a molecule that aids the function of an enzyme
how do coenzymes work?
by transferring a chemical group from one molecule to another
what is NADP?
a coenzyme used in photosynthesis.
it transfers hydrogen from one molecule to another - this means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule
what are examples of coenzymes used in respiration?
NAD
coenzyme A
FAD
what do NAD and FAD do?
transfer hydrogen from one molecule to another - this means they can reduce or oxidise a molecule
what does coenzyme A do?
transfer acetate between molecules
what are chloroplasts?
flattened organelles surrounded by a double membrane. they are found in plant cells
how are the thylakoids structured within the chloroplasts?
they are stacked up in the chloroplasts into structures called grana. the grana are linked together by bits of thylakoid membrane called lamellae
how do chloroplasts absorb light energy?
they contain photosynthetic pigments. these are coloured substances that absorb the light energy needed for photosynthesis. the pigments are found in the thylakoid membranes - they’re attached to proteins. the protein and pigment is called a photosystem
what wavelength does each photosystem absorb best?
PSI - 700 nm
PSII - 680 nm
what is the stroma?
a gel-like substance contained within the inner membrane of the chloroplast and surrounding the thylakoids.
what does the stroma contain?
enzymes, sugars and organic acids
what happens to carbohydrates produced by photosynthesis?
they are stored as starch grains in the stroma
what are the 2 stages of photosynthesis?
the light-dependent reaction
the light-independent reaction
where does the light dependent reaction take place?
it takes place in the thylakoid membranes of the chloroplasts
what happens in the LDR?
chlorophyll is photoionised
ATP and NADPH is formed
H2O is oxidised to O2
what happens when chlorophyll is photoionised?
light energy is absorbed by chlorophyll in the photosystems
the light energy excites electrons in the chlorophyll, leading to eventual release from the molecule
how is ATP and NADPH formed in the LDR?
some of the energy from the released electrons is used to add a phosphate group to ADP and some is used to reduce NADP.
what is the light-independent reaction also known as?
the Calvin cycle
where does the Calvin cycle take place?
it takes place in the stroma of the chloroplast
what happens to the products of the LDR in the Calvin cycle?
ATP transfers energy and NADPH transfers hydrogen to make simple sugars from CO2
what is the energy from the photoionisation of chlorophyll in the LDR used for?
phosphorylation
making reduced NADP from NADP
photolysis
what is phosphorylation?
making ATP from ADP and inorganic phosphate
what is photolysis?
splitting water into protons (H+ ions), electrons and oxygen
how are photosystems in the thylakoid membrane linked?
they are linked by electron carriers
what are electron carriers?
proteins that transfer electrons
what is an electron transport chain?
a chain of proteins through which excited electrons flow. its formed from the photosystems and electron carriers
what are the steps of non-cyclic photophosphorylation?
- light energy excites electrons in chlorophyll
- photolysis of water produces protons (H+ ions), electrons and O2
- energy from the excited electrons make ATP
- energy from excited electrons generates reduced NADP
what happens when light energy excites electrons in chlorophyll?
light energy is absorbed by PSII
the light energy excites electrons in chlorophyll
the electrons move to a higher energy level
these high-energy electrons are released from the chlorophyll and move down the electron transport chain to PSI
why does water need to be photolysed in the LDR?
as the excited electrons from chlorophyll leave PSII to move down the electron transport chain, they must be replaced
what happens in the photolysis of water?
light energy splits water into protons (H+ ions), electrons and oxygen
H2O –> 2H+ + 1/2O2
how does energy from the excited electrons make ATP?
the excited electrons lose energy as they move down the electron transport chain
this energy is used to transport protons into the thylakoid, creating a higher conc. than the stroma. forming a proton gradient across the thylakoid membrane
protons move down their conc. gradient into the stroma, via the enzyme ATP synthase, which is embedded in the thylakoid membrane.
the energy from this movement combines ADP and Pi to form ATP
how does energy from the excited electrons generate reduced NADP?
light energy is absorbed by PSI, which excites the electrons again to an even higher energy level
finally, the electrons are transferred to NADP, along with the proton from the stroma, to form NADPH
what is chemiosmosis?
the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis
how does cyclic photophosphorylation differ from non-cyclic?
it only uses PSI. the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers. this means the electrons are recycled and can repeatedly flow through PSI. this process doesn’t produce any NADPH or O 2 - only small amounts of ATP
what are the stages of the Calvin cycle?
- carbon fixation
- reduction
- regeneration
how is glycerate 3-phosphate made in the Calvin cycle?
CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast
it combines with ribulose bisphosphate. this reaction is catalysed by the enzyme rubisco
this gives an unstable 6-carbon compound, which quickly breaks down into 2 molecules of glycerate 3-phosphate
how big is ribulose bisphosphate?
it’s a 5 carbon compound
how big is glycerate 3-phosphate (GP)?
it’s a 3 carbon compound
how is triose phosphate made in the Calvin cycle?
the hydrolysis of ATP from the LDR provides energy to turn GP into triose phosphate
H+ ions from NADPH are also needed to form TP
some TP is then converted into useful organic compounds (e.g. glucose) and some continues in the Calvin cycle to regenerate RuBP
how is RuBP regenerated?
5 out of every 6 molecules of TP produced aren’t used to make hexose sugars, but to reduce RuBP
regenerating RuBP uses the rest of the ATP produced by the LDR
Why is the Calvin cycle needed?
it’s the starting point for making all the organic substances a plant needs.
TP and GP molecules are used to make carbohydrates, lipids and amino acids
how are GP and TP used to make carbohydrates?
hexose sugars are made by joining 2 TP molecules together and larger carbohydrates are made by joining hexose sugars together in different ways
how are GP and TP used to make lipids?
these are made using glycerol, which is synthesised from TP and fatty acids, which are synthesised from GP
how are GP and TP used to make amino acids?
some amino acids are made from GP
why does the Calvin cycle need to turn 6 times to make 1 hexose sugar?
3 turns = 6 TP molecules
5 TP molecules are needed to make RuBP
so 1 TP molecule is left
2 TP molecules are needed for a hexose molecule
so the cycle must turn 6 times
18 ATP and 12 NADPH is needed from the LDR
what are the ideal conditions for most plants?
high light intensity of a certain wavelength
temperature around 25*C
carbon dioxide at 0.4%
Why is high light intensity needed for photosynthesis?
light is needed to provide the energy for the light-dependent reaction - the higher the intensity of the light, the ore energy it provides
why are only certain wavelengths used for photosynthesis?
the photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb the red and blue light in sunlight.
green light is reflected
why is the optimum temperature 25*C for most plants?
photosynthesis involves enzymes. if the temperature falls below 10 C the enzymes become inactive, but if the temperature is more than 45C they may start to denature
stomata close at high temperatures to avoid losing too much water. this causes photosynthesis to slow down because less CO2 enters the leaf
why is the ideal carbon dioxide 0.4%?
carbon dioxide makes up 0.04% of the gases in the atmosphere
increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close
how does water affect photosynthesis?
too little - photosynthesis has to stop but too much and the soil becomes waterlogged (reducing the uptake of minerals such as magnesium, which is needed to make chlorophyll a)
what factors can limit photosynthesis?
light
temperature
CO2
what does it mean if a factor is limiting?
it is slowing down photosynthesis
if light intensity is limiting, than as it is increased so does the rate of photosynthesis
what is the saturation point?
increasing a factor anymore after this point makes no difference to the rate of photosynthesis, something else has become the limiting factor. a graph levels off at this point
how do agricultural growers create optimum conditions?
in greenhouses or poly tunnels
how is carbon dioxide concentration managed in a greenhouse?
CO2 is added to the air, e.g. by burning a small amount of propane in a CO2 generator
how is light intensity managed in a greenhouse?
light can get in through the glass
lamps provide light at the night-time
how is temperature managed in a greenhouse?
greenhouses trap heat energy from sunlight, which warms the air. heaters and cooling systems can also be used to keep a constant optimum temperature, and air circulation systems make sure the temperature is even throughout the greenhouse
why do plants with more CO2 grow more?
plants use CO2 to produce glucose by photosynthesis. the more CO2 they have, the more glucose they can produce, meaning they can respire more and so have more ATP for DNA replication, cell division and protein synthesis
what is the exam technique for the LDR?
- light energy excites electrons in chlorophyll
- electrons pass down electron transfer chain
- electrons reduce carriers in a series of redox reactions
- electron transfer chain associated with thylakoids
- energy released at decreasing energy levels
- ATP is generated from ADP and inorganic phosphate (ATP synthase)
- electrons emitted from chlorophyll molecule
what happens in the carbon fixation step of the Calvin Cycle?
the enzyme Rubisco catalyses the reaction of Ribulose bisphosphate and CO2 into 2 x glycerate 3-phosphate
what happens in the reduction step of the Calvin Cycle?
reduced NADP from the LDR reduces glycerate 3-phosphate into triose phosphate using energy from ATP
what happens in the regeneration step of the Calvin Cycle?
some triose phosphate is converted into useful organic compounds e.g. glucose. some is regenerated back into Ribulose Bisphosphate using energy from ATP to maintain its supply
what is the exam technique for the Calvin Cycle?
CO2 combines with RuBP produces GP GP reduced to TP using NADPH using energy from ATP TP converted to glucose/ hexose/ RuBP/ named organic substance
how can photosynthesis be limited by CO2 concentration?
CO2 + RuBP —–> 2GP
how can photosynthesis be limited by light intensity?
light is needed in the LDR
excitation of electrons
photolysis
how can photosynthesis be limited by temperature?
ATP synthase
RUBISCO
how can photosynthesis be limited by water availability?
photolysis
how can photosynthesis be monitored?
measuring:
presence of starch (iodine) - starch being made from glucose
volume of O2 released - O2 released from photosynthesis/ min
volume of CO2 released - add hydrogen carbonate to solution as carbon used up pH increases
how can the rate of photosynthesis be measured?
volume of O2 produced per minute
what do pigments do in plants leaves?
plants contain several different photosynthetic pigments in their leaves. each pigment absorbs a different wavelength of light.
more than 1 type means increased range of wavelengths that can be absorbed
other pigments do other things like protect leaves from UV
How can you determine what pigments are present in the leaves of a plant?
TLC - thin layer chromatography
what does TLC involve?
a mobile phase - where molecules can move. In TLC this is a liquid solvent
a stationary phase - where molecules can’t move. In TLC this consists of a solid plate with a thin layer of gel on top
What happens in TLC?
a sample of pigments can be extracted from the plant and put on the plate.
plate placed vertically in solvent
solvent moves up through gel, carrying dissolved pigments with it
some pigments travel faster or further through the gel, which separates them out
How are pigments identified in TLC?
calculating Rf value and looking it up in a database. this is the distance a substance has moved through the gel in reaction to the solvent.
How to prepare the solution for TLC ?
grind up leaves with anhydrous sodium sulphate, add few drops of propanone
transfer liquid to test tube , add petroleum ether and shake
a layer of pigments and petroleum ether will form on top
transfer top layer into test tube with anhydrous sodium sulphate.
How to carry out TLC?
draw horizontal pencil line near bottom of TLC plate
build a single concentrated spot from the solution. this is the point of origin
once dry place in glass container containing solvent so origin is above it.
put lid on container and leave to develop. as solvent spreads pigment moves with it at different rates and separates.
what is in the solvent used for the TLC to compare pigments present in shade-tolerant and intolerant plants?
mixture of propanone, cyclohexane and petroleum ether
what to do when mobile phase has stopped moving in the TLC?
mark solvent front with a pencil and leave plate to dry
there should be several new coloured spots on the chromatography plate between point of origin and solvent front. these are the separated pigments.
Rf values can be calculated and looked up to identify pigments
what is the formula for the Rf value?
distance travelled by spot/ distance travelled by solvent
How can the activity of dehydrogenase be investigated?
adding a redox indicator dye to extracts of chloroplasts. the dye acts as an electron acceptor and gets reduced by dehydrogenase in the chloroplasts. as the dye is reduced there is a colour change. e.g. DCPIP turns from blue to colourless
rate can be measured using rate of colour change with a a colorimeter
how to prepare chloroplast extract to test the effects of light intensity on dehydrogenase?
cut up leaves, removing stalks
grind up using pestle and mortar in chilled isolation solution
filter liquid into beaker
transfer liquid into centrifuge tubes and spin for 10 mins so chloroplasts ether at bottom in pellet
get rid of liquid, leaving pellet
re-suspend pellets i fresh, chilled isolation solution.
keep on ice
How to carry out experiment to investigate effects of light intensity on dehydrogenase?
set up colorimeter with red filter and zero it using cuvette contain gin chloroplast extract and distilled water
put test tube with set volume of chloroplast extract and DCPIP in test tube rack set distance from lamp and mix
immediately take sample and add to clean cuvette in colorimeter and record absorbance
repeat every 2 mins for 10 mins
repeat whole experiment for different distances from lamp
What happens in the investigation of the effects of light intensity on dehydrogenase?
as dehydrogenase activity is taking place, absorbance will decrease as DCPIP is reduced to colourless
faster absorbance decreases, the faster the rate.
plot absorbance time graph for each distance and compare
what are the similarities of the 2 types of respiration?
they both produce ATP (anaerobic respiration produces less)
both start with the glycolysis
what is glycolysis?
splitting 1 molecule of glucose into 2 smaller molecules of pyruvate
glycolysis is the 1st stage and doesn’t require oxygen
where does glycolysis happen?
in the cytoplasm
what are the 2 stages of glycolysis?
phosphorylation
oxidation
what happens in phosphorylation in glycolysis?
glucose is phosphorylated using phosphate from 2 ATP
this produces 1 glucose phosphate and 2 ADP
phosphates cause instability it is then split into 2 triose phosphates
what happens in oxidation in glycolysis?
triose phosphate is oxidised forming 2 pyruvate
NAD+ collects the hydrogen ions forming 2 NADH
4 ATP are produced from 4 ADP but 2 were used up in phosphorylation so there’s a net gain of 2 ATP
what happens to the products of glycolysis in aerobic respiration?
the 2 NADH go to oxidative phosphorylation
the 2 pyruvate are actively transported into the matrix of the mitochondria for the link reaction
what happens in glycolysis in anaerobic respiration in animals?
the pyruvate is converted into lactate in animals and some bacteria using NADH
what happens in glycolysis in anaerobic respiration in plants?
the pyruvate is converted into ethanol and CO2 (decarboxylation) in plants and yeast using NADH
why is ethanol or lactate produced in anaerobic respiration?
NADH is regenerated into NAD+. this means glycolysis can continue even when there isn’t much oxygen around, so a small amount of ATP can still be produced to keep some biological processes going.
what happens in the Link reaction?
pyruvate is decarboxylated (CO2) is removed
pyruvate is oxidised to form acetate and NAD+ is reduced to NADH
acetate is combined with coenzyme A to form acetyl CoA
no ATP is produced
how many times does the link reaction occur?
2 pyruvate molecules are made in glycolysis so link and krebs happen twice for every glucose
what are the final products of glycolysis?
2 ATP
2 NADH
2 pyruvate
what are the final products of the link reaction for 1 glucose?
2 acetyl coA - for krebs
2 CO2 - as waste
2 NADH - for oxidative phosphorylation
where does the link reaction and krebs cycle take place?
in the matrix of the mitochondria
what happens in the krebs cycle?
acetyl CoA combines with a 4 carbon molecule to form a 6 carbon molecule
coenzyme A goes back to link
6C converted to 5C by decarboxylation and dehydrogenation, removing CO2 and H+ to reduce NAD+ to NADH
decarboxylation and dehydrogenation occur again producing CO2, ATP, FADH2, 2 NADH and 4C which starts the cycle again
how is ATP produced in the krebs cycle?
by the direct transfer of a phosphate group from an intermediate compound to ADP. when a phosphate group is directly transferred from 1 molecule to another it’s called substrate-level phosphorylation
what are the products of 1 krebs cycle?
coenzyme A - reused in link 4C molecule - for next Krebs cycle 2 CO2 - waste ATP 3 NADH - oxidative phosphorylation FADH2 - oxidative phosphorylation
what is oxidative phosphorylation?
the process where energy carried by electrons, from NADH and FADH2 is used to make ATP
it involves the electron transport chain and chemiosis
what happens in oxidative phosphorylation?
H+ and electrons are released from NADH and FADH2 (oxidation)
electrons move down ETC losing energy at each carrier
this energy is used to pump protons from matrix into inter membrane space
proton conc. is higher in the IM space forming electrochemical gradient
protons move down gradient via ATP synthase
what is chemiosis?
the process of ATP production driven by the movement of H+ across a membrane, due to electrons moving down ETC
Why is oxygen needed in aerobic respiration?
it acts as the final electron acceptor, it takes the electron from the last proton pump in the ETC and H+ ions that have come through ATP synthase to make water
How to investigate the effects of temperature on aerobic yeast respiration?
add known volume and conc. of substrate solution to test tube. add known vol of buffer solution
leave in water bath for 10 mins
add known mass of dried yeast and stir for 2 mins
add bung with gas syringe attached
start stopwatch record vol of CO2 present at regular intervals for set amount of time
repeat 3 times for each temp.
calculate mean CO2 production at each temp
why is a pH buffer added in the investigation of the effects of temperature on aerobic yeast respiration?
to keep pH constant at optimum
why do you leave the test tubes in the water bath for 10 mins in the investigation of the effects of temperature on aerobic yeast respiration?
to allow the temperature of the substrate to stabilise
what is the control experiment in the investigation of the effects of temperature on aerobic yeast respiration?
a control should be set up at each temperature being investigated, where no yeast is present. no CO2 should be formed without the yeast
How to investigate the effects of temperature on anaerobic yeast respiration?
set up apparatus same way as in aerobic experiment
trickle liquid paraffin down the inside of test tube so that covers surface, stopping oxygen getting in
attach bung with gas syringe and carry out rest of experiment as normal
what can respirometers be used for?
to indicate the rate of aerobic respiration by measuring the amount of oxygen consumed by an organism over a period of time
how to carry out the respirometer investigation on woodlice?
partially submerge apparatus in water at optimum temp for woodlice enzymes
set up control with glass beads of the same mass
give 1o mins with apparatus open to equilibrate
then close tap and attach syringe
use syringe to reset manometer. record reading from volume scale on syringe
as respiration occurs vol of air decreases as CO2 absorbed by KOH and oxygen used up in respiration
pressure also reduces so fluid in manometer moves
after a set time reset manometer and record reading on syringe to find difference in volume of oxygen
what is the equation for anaerobic respiration?
glucose —> CO2 + lactic acid + energy(little)
what are the steps of aerobic respiration?
glycolysis
link reaction
krebs cycle
oxidative phosphorylation
where does oxidative phosphorylation take place?
through the inner membrane of the cristae
why does anaerobic respiration occur?
no final electron acceptor in ox phos
electrons can’t leave ETC, so electrons become backed up until no more can enter
NADH and FADH2 can’t be oxidised to form NAD+ and FAD+ needed for link and krebs.
so NAD+ needs to be regenerated in glycolysis
