photosynthesis Flashcards
structure of the chloroplast
adaptations of the chloroplasts
-thylakoid membranes give a large surface area for the attachment of chlorophyll, electron carriers and enzymes for the LDR.
-protein network in grana holds chlorophyll precisely to allow maximum light absorption.
-granal membranes have ATP synthase to catalyse the production of ATP, selectively permeable to ensure a proton gradient.
-contain DNA and ribosomes to manufacture some of the proteins involved in the LDR.
where does the light dependent stage take place
thylakoids
-stack up to form grana, which are connected by lamellae.
-lamellae ensures the stacks of sacs are connected but distanced from each other.
-membranes of the grana create a large surface area to increase the number of light dependent reactions that can occur
photolysis
a chlorophyll molecule absorbs a photon of light, splitting water into protons, electrons and oxygen
-the electrons are passed along a chain of electron carrier proteins
-the hydrogens are picked up by NADP (co-enzyme) to form reduced NADP and is used in the LIR
-oxygen is either used for respiration or diffuses out of the leaf through the stomata
photoionisation of chlorophyll
light energy is absorbed by the chlorophyll, and the energy results in electrons becoming excited and raising up an energy level to leave the chlorophyll.
-therefore the chlorophyll has been ionised by light.
-some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis
explain how photoexcited electrons move along the electron transfer chain, and hence how ATP and reduced NADP and produced
transfer of electrons between photosystems results in the pumping action of protons across the thylakoid membrane from the stroma to the lumen- creation of proton gradient, essential for ATP production. NADP needs to be present for a protein molecule to function efficiently. NADP accepts the electrons from ferredoxin and a H+ and NADP becomes reduced NADP.
production of ATP is dependent on two structures
- cytochrome proton pump- pumps H+ into the thylakoid lumen to create the proton gradient
- ATP synthase- catalyses the addition of Pi to ADP when driven to rotate by the flow of the H+ into the stroma
chemiosmosis
the electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane- electron transfer chain.
as they move along they release energy and some of the energy from electrons is used to pump the protons across the chloroplast membranes.
creates a high concentration of protons in the thylakoid lumen compared to the stroma on the other side of the membrane- known as an electrochemical gradient.
protons can only pass through ATP synthase, which catalyses the reaction of ADP + Pi to form ATP- due to the protons diffusing through, causes the change in shape of ATP synthase which provides energy for the catalysing of ATP.
protons then move back down their electrochemical gradient through the ATP synthase channel, some protons then combine with the co-enzyme NADP to become reduced NADP.
-because protons move from a high to low concentration gradient, this is known as chemiosmosis
LIR
chemical reactions that convert carbon dioxide into glucose
where does the light independent stage occur
stroma- contains enzyme RuBisCO which catalyses this reaction.
-this stage is temperature sensitive as it involves enzymes
what products are needed for the LIR and why
carbon dioxide, reduced NADP and ATP to form a hexose sugar.
-ATP is hydrolysed to provide energy for this reaction
-reduced NADP is donated the hydrogen to reduce molecules GP in the cycle
stages of LIR- calvin cycle
-carbon dioxide (from atmosphere diffusing in through stomata in the leaves) reacts with the RuBP to form 2 molecules of GP (a 3 carbon compound). this reaction is catalysed by the enzyme RuBisCO
-GP is reduced to TP using energy from ATP being hydrolysed and by accepting the released hydrogen from the reduced NADP. 2 molecules of TP produced (3C compounds)
-some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances (e.g. glucose, starch, sucrose)- 1 carbon leaves cycle each time, 6 cycles to produce a hexose sugar
-rest of the molecule is used to regenerate RuBP, with the energy of ATP
why is the conversion of GP to TP a reduction reaction
because a hydrogen is gained from the reduced NADP- causing the reduced NADP to become re-oxidised because it is donatingg the hydrogen
what is a limiting factor
any factor that reduces the rate of photosynthesis
-temperature (LIR, enzyme controlled reaction) , carbon dioxide concentration (one of the reactants entering the calvin cycle) , light intensity (LDR, dependent on light for photolysis and photoionisation).
-when there is a positive correlation, x-axis is the limiting factor, however when the line begins to plateau, the x-axis is no longer the limiting factor and it must be one of the 2 other factors
how do farmers seek to maximise productivity of land and maximise its profits
-growing plants under artificial lighting to maximise light intensity
-heating a greenhouse to increase the temperature
-burning fuel to release more carbon dioxide
-if the extra growth from photosynthesis is minimal, it will not be cost effective to pay for heating/lighting/fuel
