Required Practicals Flashcards
Required practical 1: Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction.
The rate of reaction of an enzyme-controlled reaction is influenced by different factors: the temperature, pH, concentration of the substrate, and the concentration of the enzyme.
2 control samples - one hydrolysed by hydrochloric acid, one distilled water sample
3 test tubes of milk at different temperatures
Add trypsin and time how long it takes to completely hydrolyse (turn colourless)
Rate of reaction = 1/mean time
Required practical 2: Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index.
Mitotic index = number of cells with visible chromosomes/total number of cells in sample
Root is site of rapid growth, so many cells will be at different stages of mitosis
Add stain to make the chromosomes visible
Make sure there are no air bubbles in the slide which may distort the image, and that the coverslip doesn’t slide sideways which could damage the chromosomes.
Required practical 3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue.
Calibration curves are graphs used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations
Make a series of dilutions of 1M sucrose solution. These should be at 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0M sucrose. Dilute using distilled water.
Calculate the percentage change in mass for each sucrose solution for each identically sized potato chip
The point at which the line of best fit crosses the x axis (zero change in mass) indicates the point at which the solution is isotonic. This is when the water potential of sucrose solution is the same as the water potential of the potato tissue, so there is no net movement of water in or out of the potato.
Required practical 4: Investigation into the effect of a named variable on the permeability of cell-surface membranes.
The permeability of a membrane can be measured by using beetroot cells, which contain a purple pigment called betalain. When the cell-surface membrane has a higher permeability, more pigment leaks out of cells.
Using a colorimeter, measure the absorbance of each sample and plot a calibration curve
A higher absorbance indicates
higher pigment concentration, and hence a more permeable membrane.
Plot a graph of absorbance against ethanol concentration or temperature.
As the temperature increases, the permeability of the cell-surface membrane also increase as proteins in the membrane are damaged.
Ethanol causes the cell-surface membrane to rupture
Required practical 4: Investigation into the effect of a named variable on the permeability of cell-surface membranes.
The permeability of a membrane can be measured by using beetroot cells, which contain a purple pigment called betalain. When the cell-surface membrane has a higher permeability, more pigment leaks out of cells.
Using a colorimeter, measure the absorbance of each sample and plot a calibration curve
A higher absorbance indicates
higher pigment concentration, and hence a more permeable membrane.
Plot a graph of absorbance against ethanol concentration or temperature.
As the temperature increases, the permeability of the cell-surface membrane also increase as proteins in the membrane are damaged.
Ethanol causes the cell-surface membrane to rupture
Required practical 5: Dissection of animal or plant gas exchange system or mass transport system or of organ within such a system.
Cut away from fingers/self; use forceps to hold tissue whilst cutting; keep away from the edge of the desk. Use sharp knife rather than a blunt one as a blunt knife requires more force.
Use disinfectant; keep sample on dissection board; wash hands with soap after dissection
Required practical 6: Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth.
Aseptic techniques are used to avoid contamination of the sample from outside substances such as microorganisms. This is important to get reliable and repeatable data.
Sterilise wire loop with acid and bunsen burner.
Close windows and doors to prevent air currents.
Use sterile forceps to place a multi disc antibiotic ring on the plate.
DO NOT tape around the entire dish as this prevents oxygen entering and so promotes the growth of more harmful anaerobic bacteria.
Bacteria sample is incubated at 25°C. This is because incubating at 37°C (human body temperature) could enable pathogens to grow that are harmful to human
Measure the diameter of the inhibition zone (clear circle) for each antibiotic and work out the area of the inhibition zone.
