A2 practicals Flashcards
Using chromatography to investigate the pigments isolated from the leaves of plants
Draw a pencil line 1cm from the bottom of the chromatography paper (ink would mix with leaf pigments)
Grind up several leaves in a mortar with 20 drops of acetone
Use the pestle to grind up the leaf sample which releases the pigments
Use a capillary tube to extract some of the pigment and blot it onto the pencil line
Build up a concentrated spot by applying several drops, ensuring time to dry inbetween each spot
Place paper in a beaker with level of solvent below origin line. Place lid on beaker
Remove when solvent has reached the top of the paper
Mark solvent front with pencil
Calculate the Rf value for each spot and compare to databook values
Colorimetry
Zero colorimeter with a cuvette of distilled water
Make up a dilution series using known concentrations
Record absorbance using colorimeter
Plot graph of concentration against absorbance
Read off concentration from absorbance obtained
Investigation into the effect of factors affecting respiration in single-celled organism
Both aerobic and anaerobic respiration in yeast produces CO2
Put a known volume and concentration of substrate solution (e.g. glucose) into a test tube
Add a known volume of buffer solution to keep the pH constant
Place into a waterbath and set to a temp being investigated
Leave for 10 minutes to allow temperature to stabalise
Add a known mass of dried yeast and stir
Add a bung with a tube attached to a gas syringe to the top of the test tupe
Start a stop watch
At regular intervals record the volume of CO2 present in the syringe for a set amount of time (10 min)
Negative control set up at each temp with no yeast
Repeat and calculate a mean
Sampling
Use grid
Random number generator
Large sample of quadrats
Count number/frequency in each quadrat
Calculate mean per quadrat
Divide total percentage by number of samples
Effect of a named factor on the rate of dehydrogenase activity in chloroplasts
Centrifuge to obtain sediment pellet with chloroplasts
Suspend in chilled isolated solution and store on ice
Set up a colorimeter with a red filter and zero using a cuvette containing chloroplast extract and distilled water
Set up a test tube rack a set distance from a bench lamp
Switch the lamp on
Add a set volume of chloroplast extract to the tube and then a set volume of DCPIP
Mix
Immediately take a sample from the mixture and add to a clean cuvette
Record absorbance every 2 minutes for the next 10 minutes
Repeat for each distance from lamp
If dehydrogenase activity is taking place, absorbance will decrease as DCPIP gets reduced and turns from blue to colourless
Plot a graph of absorbance against time for each distance from the light source
Negative control tubes for DCPIP
One should only contain DCPIP and chilled isolation solution to show that the chloroplast extract is needed for DCPIP to change colour
Second both DCPIP and chloroplast extract wrapped in tin foil to block light to show that light is needed for DCPIP to change colour
