Practicals Flashcards
Give on way in which the student could ensure the first three beetroot cylinders were kept at 25 degrees throughout her experiment (selective permeability)
Use a thermometer and take regular measurements throughout the experiment
uncertainty
+ or - X
how do you calculate uncertainty
actual reading / true value
how can uncertainty be reduced
use equipment with a better resolution
why should beetroot have the same size/length
so there is an equal surface area to volume ratio. This means that it wont affect the rate of diffusion e.g if there was a larger surface area more beetroot would be lost
why should fresh beetroot be used rather than cooked beetroot
as the cooked beetroot will have a broken membrane so rate of diffusion will be faster
what is the purpose of a cuvette filled with water
to calibrate the colorimetre
Suggest one improvement to the design of the table and one improvement to the way she presented the data contained in the table
-same number of decimal places in the final column on the right
-name the solution in the first column
suggest and explain an advantage of carrying out this investigation at 30 degrees rather than at 20
-At 30 degrees particles have more kinetic energy which increases the movement of particles and thus the rate of osmosis
explain why the data in the table above are described as processed results
calculations have been made from raw data
rate of reaction
1 / time
how to make a control in practical measuring enzyme activity
replace enzyme solution with distilled water or boiled enzyme
Enzyme activity, trypsin, milk
-equal volumes of trypsin and milk
-place in water bath
-record time for complete hydrolysis
-repeat at increasing temperatures
what is the purpose of a calibration curve
determine the concentration of an unknown sample by comparing it to a set of values with a known concentration
what is water potential determined by
-concentration of solutes
-higher solute concentration = lower water potential
why is percentage change used
-potato chips may not all have the same starting mass
-easier for comparisons
explain the change in mass of the potato chips
-potato with a conc lower than sucrose solution (high w.p) will loose mass
the higher the permability
more pigment released
factors affecting enzyme activity
-Factors affecting enzyme action = temperature, pH, concentration of enzyme, concentration of substrate
-water bath used to equilbriate
-distilled water = absense of enzyme activity
-HCL = hydrolysed sample
-IV = temperature
-DV = time for milk to be hydrolysed
calculating mitotic index
-ratio of cells undergoing mitosis to the total number of cells in a sample
-must view cells under an optical microscope = living
-dye makes chromosomes visible so you can see what stage of the cell cycle are in
calibration curve vs dilutation series
-calibration curves are used to determine an unknown concentration of a sample but comparing it with a standard of know concentrations
-dilution series = set of samples with known concentrations
sucrose solution
Lower conc of sucrose solution = increase in mass
Higher conc of sucrose solution = decrease in mass
aseptic techniques
-wipe down surface with antibacterial cleanser
-use a bunsen burner so convetion currents move away
-flame the instruments
-close doors
-larger inhibiton zone = more bacteria killed = better antibiotic works
-low inhibiton = resistance bacteria
chromatography
-rate of migration of pigments depends on their solubility and affinity to the paper
-lower affinity = travel further up the paper
-more soluble = travel closer to the solvent front
-pigments further up the paper have a higher Rf value
dehydrogenase activity
-dehydrogenase is an enzyme found in plant chloroplasts crucial to the LDR
-allows NADP to accept electrons so it can be reduced
-When a redox indicator dye is present, such as DCPIP, electrons are accepted by this instead. The activity of dehydrogenase can therefore be investigated using DCPIP, which turns from blue to colourless when it is reduced.
-As the light intensity decreases, the rate of photosynthesis also decreases. This is because the lowered light intensity will slow the rate of photoionisation of the chlorophyll pigment, so the overall rate of the light dependent reaction will be slower.
● This means that less electrons are released by the chlorophyll, hence the DCPIP accepts less electrons. This means that it will take longer to turn from blue to colourless.
● When the DCPIP is blue, the absorbance is higher. The rate at which the absorbance decreases can therefore be used to determine the activity of the dehydrogenase enzyme. A higher rate of decrease, shown by a steep gradient on the graph, indicates that the dehydrogenase is highly active.
