Paper 2- Practical's Flashcards
(15 cards)
REQUIRED PRACTICAL 8- trate of dehydrogynase
Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts.
Talk about the context of required practical 8 and the redox reaction
During the light-dependent reactions high-energy electrons are emitted from chlorophyll
These electrons eventually reduce NADP in a reaction catalysed by dehydrogenase enzymes
When a redox indicator is added to photosynthesising material, the indicator will take up the electrons instead of the NADP; the indicator is said to become the electron acceptor
Examples of redox indicators include DCPIP and methylene blue
Accepting electrons causes redox indicator to change colour
oxidised (blue) → accepts electrons → reduced (colourless)
The rate at which a redox indicator changes colour from its oxidised (blue) state to its reduced (colourless) state can be used as a measure of the rate of dehydrogenase activity, and therefore the rate of the light-dependent reaction
Method of required practical 8
- grind up leaves with 20cm3 isolation medium in a pestle and mortar- breaks apart tissues, isolation medium prevents cell damage
- Filter the resulting liquid into a clean beaker using a funnel and filter paper
- transfer the filtered liquid into a centrifuge to get chlorophyll
- add fresh isolation medium and stir making chloroplast extract and transfer to ice cold medium
- place test tube with 0.5cm3 of chloroplast extract into a test tube rack and set up a specified distance from light
- add 5cm3 of DCPIP to chloroplast and immediately remove sample into cuvette and measure absorbance
7 repeate with different distances
Results of RP8
The graph for each light intensity should show a decrease in absorbance over time as the DCPIP becomes fully reduced and the solution turns from dark blue to green
The colourless indicator results in a green solution due to the presence of green chloroplasts
Title of RP7- chromotography
Use of chromatography to investigate the pigments isolated from leaves of different plants, eg, leaves from shade-tolerant and shade-intolerant plants or leaves of different colours.
Talk about context of photosynthetic pigments RP7
Chloroplasts contain several different photosynthetic pigments within the thylakoids,
Different pigments absorb different wavelengths of light, maximising the light energy that can be absorbed by a plant
Chlorophylls absorb wavelengths in the blue-violet and red regions of the light spectrum
They reflect green light, causing plants to appear green
Method of RP7
- Draw a straight line in pencil approximately 1 cm above the bottom of the filter paper being used
- Cut a section of leaf and place it in a mortar
- Add 20 drops of acetone and use the pestle to grind up the leaf sample and release the pigments
- Extract some of the pigment using a capillary tube and spot it onto the centre of the pencil line you have drawn
- Suspend the paper in the chromatography solvent so that the level of the solvent is below the pencil line and leave the paper until the pigments have separated
- Remove the paper from the solvent and draw a pencil line marking the point reached by the solvent
This is sometimes described as the solvent front - Calculate the Rf value for each spot; always measure to the centre of each spot
Results of RP 7
A higher Rf value indicates that molecules have a higher affinity with the liquid mobile phase, e.g. due to being:
non-polar
highly soluble in the solvent
small
A lower Rf value suggests that molecules have a higher affinity with the solid stationary phase, e.g. due to being
polar
less soluble
large
RP9- respiration
investigation into the effect of a named variable on the rate of reespiration in single celled organisms
RP9- method
- Place a set volume and concentration of glucose solution into a series of test tubes
- Add a set volume of buffer solution to each tube
This will maintain a constant pH - Place three test tubes into each water bath at range of different temperatures and leave in tubes for at least 10 mins
- Add a set volume of yeast suspension to the first test tube and stir
- Add a set volume of DCPIP to the first test tube and start the stopwatch immediately
- Stop the stopwatch when the solution loses its blue colour
- Record the time taken for a colour change to occur
Repeat
Results of RP9
A graph should be plotted of temperature against time taken for colour change
As the temperature increases, the rate of respiration should also increase; we would expect the time taken for the solution to become colourless to reduce
Alternative methods of RP9
A colorimeter could be used to measure to colour intensity of the redox indicator in a less subjective and more quantitative way
An alternative method might be to measure the volume of carbon dioxide gas produced by a yeast suspension, and use this to determine respiration rate
Nitrogen Cycle
NITROGEN FIXATION- N2 gas is converted into ammonium compounds by nitrogen-fixing bacteria; these bacteria can be free-living in the soil, or may live within root nodules of legume plants
Ammonium compounds are converted into nitrates, which are then absorbed by plants and used to build plant proteins
AMMONIFIATION- Nitrogen from living organisms is returned to the soil in the form of ammonia by the action of saprobionts such as bacteria and fungi
This ammonia forms ammonium ions in the soil
NITRIFICATION- The ammonium ions in the soil are converted into nitrates by nitrifying bacteria
DENITRIFICATION- Denitrifying bacteria use nitrates in the soil for respiration
This occurs in anaerobic conditions, such as in waterlogged soil
This process produces nitrogen gas, which returns to the atmosphere
Phosphorus cycle
phosphorus in rocks is released into the soil and into water sources in the form of phosphate ions (PO₄³⁻) due to weathering
Phosphate ions are taken up from the soil by plants, or absorbed from water by algae
Phosphate ions are transferred to consumers during feeding
Phosphate ions in waste products and dead organisms are released into the soil or water during decomposition by saprobionts
The phosphate ions can be taken up and used again by producers, or may be trapped in sediments that may turn into phosphorus-containing rock once again
