Required Practicals

Question 1

CP1: Daphnia

Why are daphnia suitable for investigating heart rate

Answer 1

they have transparent bodies so their internal organs can be observed using the light microscope

Question 2

CP1: Daphnia

Give the method for this practical

Answer 2

1. prepare 5 different concentrations of caffeine solution and a control solution of distilled water
2. add a piece of cotton to the cavity slide, then using a wide spout pipette add your large daphnia
3. Place the cavity slide onto the stage of the microscope and pipette 3 drops of your caffeine solution and observe the daphnias heart rate.
4. Count and record the heart rate by creating an S shaped graph for 15 seconds
5. Count the dots on your S shaped graph and express the heart rate as beats per minute (x4)
6. Repeat steps 2-6 with other caffeine concentrations

Question 3

CP1: Daphnia

What are some ethical considerations around using daphnia for the experiment

Answer 3

Cannot give consent
Cannot express pain

• may be more ethical to use them due to their simple nervous systems

Question 4

CP1: Daphnia

What is some care that should be taken to minimise potential harm

Answer 4

• animals should be handled gently
• examination periods should be kept as short as possible

Question 5

CP2 : Vitamin C content

what is the chemical name for Vitamin C and what is a property of it

Answer 5

Chemical name = ascorbic acid

good reducing agent and is easily oxidised

Question 6

CP2 : Vitamin C content

method to find vitamin C concentration using a titration

Answer 6

1. pipette 1cm3 of 1% blue DCPIP into a conical flask
2. fill up the burette to the 0 mark with the first type of juice
3. slowly add juice to the DCPIP using the burette, swirling with every drop
4. as soon as the DCPIP loses its colour turn of the burette tap and record the results
5. Repeat this 2 times per jucie

Question 7

CP2 : Vitamin C content

whats the
IV
DV
CV

Answer 7

IV - type of jucie
DV - volume of juice that turned DCPIP colourless
CV - Conc of DCPIP
Volume of DCPIP

Question 8

CP3 : Investigating enzyme conc

what are the
IV,DV and CV?

Answer 8

IV = conc of enzyme trypsin
DV = initial rate of reaction
CV = Volume of enzyme
Temperature
Concentration of casein

Question 9

CP3 : Investigating enzyme conc

Method to measure the initial rate of reaction of the trypsin enzyme with the milk solution

Answer 9

1. Calibrate colorimeter using distilled water in cuvette
2. Using a pipette, add 2cm3 milk solution into 5 cuvettes.
3. Then place a cuvette into the colourimeter.
4. Add 2cm3 of 2% concentration trypsin into the cuvette, ensuring no spillage.
5. Then as soon as all the trypsin has been added, start your stopwatch and start measuring the absorbance on the colourimeter.
6. Measure the absorbance every 10 seconds and record your results on the results table.
7. Repeat steps 4-6 using different trypsin concentrations.

Question 10

CP3 : Investigating enzyme conc

how do we find the initial rate of reaction of all enzyme concentrations

Answer 10

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