CP1: Daphnia
Why are daphnia suitable for investigating heart rate
they have transparent bodies so their internal organs can be observed using the light microscope
CP1: Daphnia
Give the method for this practical
- prepare 5 different concentrations of caffeine solution and a control solution of distilled water
- add a piece of cotton to the cavity slide, then using a wide spout pipette add your large daphnia
- Place the cavity slide onto the stage of the microscope and pipette 3 drops of your caffeine solution and observe the daphnias heart rate.
- Count and record the heart rate by creating an S shaped graph for 15 seconds
- Count the dots on your S shaped graph and express the heart rate as beats per minute (x4)
- Repeat steps 2-6 with other caffeine concentrations
CP1: Daphnia
What are some ethical considerations around using daphnia for the experiment
Cannot give consent
Cannot express pain
- may be more ethical to use them due to their simple nervous systems
CP1: Daphnia
What is some care that should be taken to minimise potential harm
- animals should be handled gently
- examination periods should be kept as short as possible
CP2 : Vitamin C content
what is the chemical name for Vitamin C and what is a property of it
Chemical name = ascorbic acid
good reducing agent and is easily oxidised
CP2 : Vitamin C content
method to find vitamin C concentration using a titration
- pipette 1cm3 of 1% blue DCPIP into a conical flask
- fill up the burette to the 0 mark with the first type of juice
- slowly add juice to the DCPIP using the burette, swirling with every drop
- as soon as the DCPIP loses its colour turn of the burette tap and record the results
- Repeat this 2 times per jucie
CP2 : Vitamin C content
whats the
IV
DV
CV
IV - type of jucie
DV - volume of juice that turned DCPIP colourless
CV - Conc of DCPIP
Volume of DCPIP
CP3 : Investigating enzyme conc
what are the
IV,DV and CV?
IV = conc of enzyme trypsin
DV = initial rate of reaction
CV = Volume of enzyme
Temperature
Concentration of casein
CP3 : Investigating enzyme conc
Method to measure the initial rate of reaction of the trypsin enzyme with the milk solution
- Calibrate colorimeter using distilled water in cuvette
- Using a pipette, add 2cm3 milk solution into 5 cuvettes.
- Then place a cuvette into the colourimeter.
- Add 2cm3 of 2% concentration trypsin into the cuvette, ensuring no spillage.
- Then as soon as all the trypsin has been added, start your stopwatch and start measuring the absorbance on the colourimeter.
- Measure the absorbance every 10 seconds and record your results on the results table.
- Repeat steps 4-6 using different trypsin concentrations.
CP3 : Investigating enzyme conc
how do we find the initial rate of reaction of all enzyme concentrations
plot a graph for each conc
use a tangent to find the gradient and mean rate of reaction for each conc graph
plot the average rate of all graphs on one graph
