Core Practical. UNIT 1- Effect of caffeine on heart-beat rate in Daphnia.

* Daphnia magna –Water fleas- are semi-transparent fresh water crustacean. They are filter feeders and can survive in culture by eating algae, bacteria or yeast.

They are used in experiments as a model system in that they are a simpler way at looking at a scientific problem; in this case looking at the effect of caffeine on heart beat rate.

* Advantages of using Daphnia; easy to culture/keep, study and inexpensive.

* Disadvantage of using Daphnia; not closely related to humans so results may not be relevant. Since the water fleas are easy to stress, results again may be misleading.

* Effect of caffeine. Plants produce caffeine as an insecticide. Cocoa, coffee and tea have been used for 100’s of years to produce ‘pick me up drinks’. These days it is used as a flavour enhancer in a wide range of soft drinks. In addition it is used in medicinal uses in aspirin preparations and is found in weight loss drinks and as a stimulant in Pro-Plus and Red Bull. Low doses stimulate the central nervous system, high doses produce restlessness, tremors, headache and insomnia.

Caffeine mimics some of the effects of the adrenaline and noradrenaline on the heart. It can increase the rate of contraction of the ventricles, leading to an increase in cardiac output.

* Culture of Daphnia ; it may be killed by chlorine in tap water and therefore pond water is recommended to culture the water fleas in.

* Outline Method;

1. Place Daphnia on cavity/depression slide with pond water/zero caffeine.

2. Focus on heart using microscope.

3. Use a stopwatch to time 20s and count the number of heart beats in several periods of 20s. The rate is generally very high so count the beats by making dots on a piece of paper in the shape of the letter S. Count the dots and express heart rate as number of beats/minute.

4. Repeats.

5. Place Daphnia on new cavity slide with lowest caffeine concentration; repeat steps 2-4.

6. Range of caffeine concentration s used. 0.1%-0.5%.

7. Variables; Temperature, genotype, age, size and gender.

8. Good idea to carry out a pilot xperiment first, in order to judge the right range of caffeine concentrations to use.

* Safety aspects

With Daphnia culured in the laboratory, there are little hazard associated with its culture. However, care is needed when using caffeine as it is harmful if swallowed

*Ethical considerations;

For;

1. As an invertebrate it will have a simple nervous system-therefore reduced amount of pain.

2. As an Invertebrate is used, we do not have to use mammals.

3. Transparent- therefore heart visible without need for dissection.

4. Bred for fish food- therefore will die anyway.

5. Abundant in nature- therefore little threat of extinction if taking some samples for these experiments.

Against;

1. use of any animal is wrong.

2. The water flea may feel pain.