photosynthesis Flashcards
light dependent stage
the light enters photosystem two through absorption through the chlorophyll within the photosystem which is situated in the folds of the thylakoid membrane.
this light energy causes an electron to become excited and leave the photosystem, moving up an energy system. this electron will now move along a series of transport proteins called the electron transport chain. it will move from a high to a low energy level. whilst this is happening, the loss of electrons in PS2 is accounted for through the process of photolysis (splitting of water using light) which produces protons electrons and oxygen. the o2 is disapated and the protons are used to create a proton gradient.
the energy lost by electrons that move along etc is used to pump H ions from stroma to thylakoids creating a gradient.
the ions then move down ATP synthase down their conc gradient forming ATP through the phosphorylation of ADP- chemisosmosis. light absorbed by PS1 which releases another electrons which joins NADP to form NADPH.
Calvin cycle
in the stroma C02 from the atmosphere is fixed to RuBP a five carbon molecule forming 6C intermediate. this reaction is catalysed by rubisco. 6c intermediate is unstable so immediately breaks down into 2, 3C molecules.
GP uses energy from ATP hydrolysis and hydrogen from reduced NADP to reduce GP to TP.
1/6 of TP molecules is used to form useful products like hexose phosphates which can be used to produce starch cellulose or sucrose
can be converted to glycerol and GP to fatty acids which join to form lipids useful for formation of amino acids for protein synthesis.
5/6 of TP is used in the reformation of RuBP.
chemiosmosis
during the ldr there isa higher. concentration of protons in the thylakoid membrane than in the stroma
the membrane is impremeable to H+ so can only mve through via the ion channel which is in the ATP synthase
this process also mean that ATP is released from ADP and Pi
structure of a leaf related to photosynthesis
-large surface area that absorbs as much sunlight as possible
-numerous stomata allowing gaseous exchange
define photoionisation
when chlorophyll loses an electron to become positively charged.
purpose of chemiosmosis
creates an electrochemical gradient
for protons produced by photolysis to move down their conc gradient so that it can move through ATP synthase and form ATP.
adaptation of chloroplasts
the thylakoids provide a large surface area to allow maximum light absorption.
PS1 absorbs light at a higher wavelength compared with PS2. these photosystems are in the membrane of the thylakoids.
measuring rate of photosynthesis- dependent variables
1)volume of oxygen PRODUCED
this can be measured by counting bubbles produced by plant during photosynthesis across certain time period
adding DCPIP to measure rate of decolourisation
2) volume of carbon dioxide ABSORBED
cover leaves and shoots in a plastic bag and measure with CO2 probe over a defined time period.
why does a photosystem contain multiple pigments
so that light absorption can be maximised because different wavelengths of light can be absorbed.
where does LDR take place
in the thylakoid membrane
where does the LIR take place
in the stroma
how is ATP produced in LDR
when light enters PS2 an electron is excited and moves along the ETC releasing energy. this energy is used to establish a proton gradient between the thylakoid and the stroma. the protons move down conc gradient through chemiosmosis in ATP synthase channel. this process causes ADP to be phosphorylated into ATP.
how is NADP produced in LIR
H ions are a product of photolysis
these are added to NADP to reduce it to NADPH
how are products of LDR used in LIR
ATP supplies energy for the reduction of GP into TP by hydrolysis of ATP into ADP and Pi
phosphate from ATP is used for production of RuBP
NADPH provides reducing power for reduction of GP to TP
what can be a limiting factor of photosynthesis
light intensity
co2 conc
temp
water supply
light intensity
the rate of photosynthesis increases as light intensity increases
at some poin as light intensity continues to increase relationship between light intenisty and rate of
chromatography
-draw a straight line approx 1cm above the bottom of filter paper (ink shouldnt be used as it obscures the results by mixing with the leaf pigments)
- cut a section of a leaf and place it in a mortar
- add 20 drops of acetone and use a pestle to grind up the leaf to release the pigments
-use a capillery tube to extract some pigment and blot it onto the centre of pencil line
-suspend paper in solvent so that the level of liquid doesnt lie above pencil line and leave until solvent has run up the paper
-remove paper draw a pencil marking where the solvent ran up to
-pigment shouldve seperated
-work out rf value of each spot always measure centre of each spot
why would heat stress become a limiting factor in the rate of photosynthesis
less or no ATP
less or no NADP
(slowing of LDR)
why would a decrease in rubisco activity reduce rate of photosynthesis
less C02 reacts with RuBP so less GP formed
why is ATP a more suitable energy source compared with glucose
energy more rapidly released in a single reaction
energy released in smaller, more useful quantities
