Practicals Flashcards
Common control variables
Volume/Concentration/pH/Temperature/Time/Mass/Surface
area/Species of organism (e.g. all same potatoes)
Enzyme rate of reaction
• You will set up an enzyme controlled reaction, add substrate
and enzyme and often something to see a colour change.
• Investigate one variable e.g. pH,
Temp or concentration
• Leave the reaction for a fixed
amount of time, or measure at
regular time intervals
• Calculate the rate of reaction
Root tip squash
• Count cells from many fields of
view to obtain a representative
sample
• Calculate a mean
• Same age plant/Same type of
plant
• Mitotic Index =
Number of cells in mitosis
Total number of cells
Why do you squash root tip?
Single layer of cells so light can pass through
Why might MI not be the same
Different plant
Diff part of root
Diff age of plant
Water potential in plants
• Make a dilution series of different
concentrations
• Cut plant to same length and volume
• Pat dry and excess liquid
• Measure initial mass
• Add plant tissue to different
concentrations and wait a specific
amount of time
• Remove the plant and pat dry
• Reweight the mass
Membrane permeability
• Put plant tissue into solution with varying independent variable e.g. a dilution series or range of temperatures
• Leave for a fixed period of time and measure amount of pigment/colour that has moved from the cells into the
solution
Using a colourimeter removes subjectivity:
• Use a colorimeter to determine the absorbance/transmittance
• Plot the results on a graph identify the trend
If there is no colourimeter:
• Set up a dilution series of known
concentrations
• Complete the reaction
• Use a colour scale of the known
concentration solutions to use as a
colour standard/comparison
How do different things affect permeability
• Temperature – too hot and proteins in the
membrane denature leaving gaps, the
phospholipids have more KE and separate
leaving gaps. Higher temp = more
permeability
• pH – High/Low pH denatures membrane
proteins increasing fluidity and
permeability
• Alcohol – dissolves phospholipids increases
permeability
Dissection
• Wash hands with soap
• Point a scalpel down/away from
you
• Cut with the scalpel pointing away
from you
• Cut on a white tile
• Dispose of dissected tissue in a separate bag/container
• Disinfect used equipment
Antibiotic resistance/aseptic technique
• Wash hands with soap
• Use a sterile pipette to inoculate
culture
• Flame spreader (loop) to kil bacteria
• Open petri dish at an angle while
pipetting
• Disinfect used equipment (loops/spreaders) in sterile solution
• Work near a Bunsen updraft
Zone of inhibition
Area of a circle
Number of cells in a culture
Starting number of cells x 2^number of divisions
