CORE PRACTICALS SNAB A LEVEL BIOLOGY
CP Name Procedure specifics (mark scheme) Control variables
1 Effect of caffeine on HR in Daphnia Suspend Daphnia in cotton wool to limit movement Size, age, type of Daphnia
Determine base heart rate in absence of caffeine Temperature
Use a range of caffeine solutions (e.g., made with pH
dilutions)
Leave to acclimatise for at least 5 minutes in each
sample
Specific method to count heart rate (dots on a piece of
paper)
Repeats/replicates
ETHICAL CONSIDERATIONS TO USING DAPHNIA
2 Vitamin C content of food and drink Specified volume of DCPIP (indicator) into a conical Temperature
flask Volume and concentration of DCPIP
Burette filled with fruit juice, take a note of start value
and then record the volume required to decolourise
DCPIP (blue to colourless)
Repeat for each fruit juice
Determine vitamin C concentration by comparing with
solution of known vitamin C concentration
3 Membrane permeability (beetroot) Cut at least 5 samples of beetroot Temperature – keep all in a water bath
Ensure all samples have the same surface Age/type of beetroot used (identical for
area/mass/source all samples)
Leave samples in different dilutions of ethanol for a
suitable time period
Measure permeability of cell membranes via the use
of a colorimeter
Calibrate colorimeter initially using distilled water
, Replicates/repeats to calculate mean
4 Enzyme and substrate concentrations Range of concentrations of an enzyme (at least 5) pH
Ensure that substrate concentration does not become Temperature
the limiting factor (or vice versa if substrate
concentration is the independent variable)
Mix the two together
Measure dependent variable over time (for example,
the collection of gas via an upturned burette in a water
bath)
Measure initial rate by recording data at specific time
intervals
Replicates/repeats at each enzyme concentration
5 Observing stages of mitosis Remove root tip with scalpel and place in hydrochloric N/a
acid to macerate the tissue
Rinse in distilled water and add a few drops of a stain,
such as acetic orcein
Place on a slide and cover with a coverslip
Calculate the mitotic index by the number of cells
undergoing visible stages of mitosis (chromosomes
present)
Safety procedure = safety goggles when handling
acid/stain
6 Identifying structures in a stem Use of forceps to pick out one or two vascular bundles
Place on microscope slide and use mounted needle to
tease apart
Add a suitable stain e.g., methylene blue, leave for 5
minutes
Draw off extra stain with filter paper, add coverslip
Examine under microscope
CP Name Procedure specifics (mark scheme) Control variables
1 Effect of caffeine on HR in Daphnia Suspend Daphnia in cotton wool to limit movement Size, age, type of Daphnia
Determine base heart rate in absence of caffeine Temperature
Use a range of caffeine solutions (e.g., made with pH
dilutions)
Leave to acclimatise for at least 5 minutes in each
sample
Specific method to count heart rate (dots on a piece of
paper)
Repeats/replicates
ETHICAL CONSIDERATIONS TO USING DAPHNIA
2 Vitamin C content of food and drink Specified volume of DCPIP (indicator) into a conical Temperature
flask Volume and concentration of DCPIP
Burette filled with fruit juice, take a note of start value
and then record the volume required to decolourise
DCPIP (blue to colourless)
Repeat for each fruit juice
Determine vitamin C concentration by comparing with
solution of known vitamin C concentration
3 Membrane permeability (beetroot) Cut at least 5 samples of beetroot Temperature – keep all in a water bath
Ensure all samples have the same surface Age/type of beetroot used (identical for
area/mass/source all samples)
Leave samples in different dilutions of ethanol for a
suitable time period
Measure permeability of cell membranes via the use
of a colorimeter
Calibrate colorimeter initially using distilled water
, Replicates/repeats to calculate mean
4 Enzyme and substrate concentrations Range of concentrations of an enzyme (at least 5) pH
Ensure that substrate concentration does not become Temperature
the limiting factor (or vice versa if substrate
concentration is the independent variable)
Mix the two together
Measure dependent variable over time (for example,
the collection of gas via an upturned burette in a water
bath)
Measure initial rate by recording data at specific time
intervals
Replicates/repeats at each enzyme concentration
5 Observing stages of mitosis Remove root tip with scalpel and place in hydrochloric N/a
acid to macerate the tissue
Rinse in distilled water and add a few drops of a stain,
such as acetic orcein
Place on a slide and cover with a coverslip
Calculate the mitotic index by the number of cells
undergoing visible stages of mitosis (chromosomes
present)
Safety procedure = safety goggles when handling
acid/stain
6 Identifying structures in a stem Use of forceps to pick out one or two vascular bundles
Place on microscope slide and use mounted needle to
tease apart
Add a suitable stain e.g., methylene blue, leave for 5
minutes
Draw off extra stain with filter paper, add coverslip
Examine under microscope
