Core practicals + ethical issues

Question 1

Aim of the daphnia experiment

Answer 1

-To investigate the effect of caffeine on the heart rate of daphnia

Question 2

Method of the daphnia experiment

Answer 2

-Dilute the caffeine solution by adding various volumes of distilled water to produce several concentrations of caffeine e.g 0.1%, 0.2% etc
-Place cotton wool on a cavity slide to minimise the movement of the daphnia
-Place one daphnia onto the cavity slide (make sure it is alive) and use filter paper to absorb water from around the daphnia
-Use a pipette to add a couple of drops of distilled water to the cavity slide, do not use a cover slide
-Place the slide under a microscope and use a stopwatch to time 60 seconds and measure the number of heart beats using the paper method (control condition)
-Then repeat this experiment using the various concentrations of caffeine solutions
-Once the experiment is over, plot a graph of daphnia heart rate against caffeine concentration

Question 3

Control variables to use in the daphnia experiment

Answer 3

-Temperature- temperature can influence heart rate
-Light intensity- strong light intensity can stress the daphnia, causing their heart rate to potentially increase
-Exposure to caffeine solution- Ensure that the time the daphnia spend in the caffeine solution is the same
-Species/ size of daphnia- different individuals can have different heart rates

Question 4

Risk assessment

Answer 4

-Risk assessment
-Biohazard (Daphnia) make sure to wash hands with soap (disinfectant) after handling
-Be careful with glassware e.g ensure it is kept away from the edge of the table and if it does break then handle with care

Question 5

Ethical concerns

Answer 5

Although the daphnia is an invertebrate and is not protected under UK animal research laws, ethical guidelines still apply:
-The researcher must avoid placing the daphnia under strong lights or in extreme temperatures
-The researcher must avoid exposing the daphnia to the caffience solution for too long
-The researcher must use a pipette in order to handle the daphnia carefully without causing them damage
-The researcher must place the daphnia back into their habitat once the experiment has concluded

Question 6

Vitamin C practical Aim

Answer 6

-To investigate the Vitamin C content of fruit juices

Question 7

Vitamin C practical Method

Answer 7

1. Gather different fruit juices e.g pineapple juice, apple juice, orange juice
2. Use a measuring cylinder to measure out 1CM3 of DCPIP solution into a test tube
3. Use a burette to slowly add the fruit juice solution drop by drop
4. Shake the solution for 5 seconds after every drop
5. Stop when the DCPIP solution decolourises, and measure the volume of fruit juice solution used
   6.Repeat the experiment using hte same fruit juice 3 times
6. Then repeat the experiment using different fruit juices and compare vitamin C content

Question 8

How does it work

Answer 8

-Vitamin C decolourises DCPIP, causing it to go from blue to colourless
-The higher the vitamin C content of the fruit juice, the less volume of fruit juice will be needed to decolourise DCPIP

Question 9

Control variables of Vitamin C practical

Answer 9

-Temperature needs to be kept the same as the temperature can affect the reaction time and decolourisation of DCPIP
-Time of shaking ensures even mixing with all of the solutions
-Same concentration/ volume of DCPIP to ensure valid comparisons between samples