the-circulatory-system investigating-heart-rate

Investigating Heart Rate

• There are a wide range of factors that influence the heart rate of an organism

• Experiments can be designed to investigate the effect of a named variable on an organism’s heart rate

• These experiments are commonly done using invertebrates, e.g. Daphnia, as well as vertebrates, e.g. humans

  • Care needs to be taken during these experiments to ensure that no test subjects are harmed

• Some of the factors that can influence heart rate include

  • Drugs

  • Caffeine

  • Alcohol

  • Sex i.e. male or female

  • Weight

  • Height

  • Temperature

  • Diet

  • Dehydration

• When designing experiments investigating a single factor, it is essential to control other variables

• Heart rate investigations can be used to study the relationship between heart structure and function

Practical: The Effect of Caffeine on Heart Rate in Daphnia

• Daphnia, also known as water fleas, are small aquatic invertebrates

• They are suitable for investigating heart date due to having transparent bodies; their internal organs, such as the heart, can be observed using a light microscope

• It is possible to investigate the impact of caffeine on the heart rate of Daphnia by placing them in a caffeine solution on a microscope slide and counting their heart beats

Daphnia internal organs can be viewed through a light microscope

Apparatus

• Light microscope

• Cavity slide

• Culture of Daphnia

• Pipette 

• Caffeine solutions at a range of concentrations

• Distilled water

• Stop watch

Method

1. Prepare five different concentrations of caffeine solution and a control solution of distilled water

   • The serial dilution technique could be used here

2. Add some pond water into the well of a cavity slide and add three drops of distilled water 

3. Select a large Daphnia and use a pipette to carefully transfer it to the cavity slide

   • You can also use a Petri dish if you do not have access to a cavity slide

4. Place the cavity slide onto the stage of a microscope and observe the animal under low power

   • The beating heart is located on the dorsal side just above the gut and in front of the brood pouch

5. Use a stopwatch to time 20 seconds, and count the number of heart beats

   • The heart beat of Daphnia is very rapid, so you can count the beats by making dots on a piece of paper

6. Count the dots and express heart rate as number of beats per minute

   • Multiply by three to convert beats per 20 seconds into beats per 60 seconds

7. Return the Daphnia to the stock culture

8. Repeat steps 3-7 with at least 5 other Daphnia individuals

9. Repeat steps 3-8 with different caffeine concentration solutions

Variations

• You can also investigate the effect of

  • Temperature 

  • Other chemicals such as alcohol (1% ethanol solution)

Results

• To analyse your results it is best to draw a graph

  • Take an average of the heart rate repeats for each caffeine concentration

  • Plot average heart rate (y axis) against caffeine concentration (x axis)

  • The graph should show a positive correlation; as caffeine concentration increases, heart rate increases

Ethical considerations

• Although they are simple organisms that may not ‘suffer’ in the same way as animals with more developed nervous systems, Daphnia still deserve respect

  • They cannot give consent to be studied

  • They cannot express pain

• Some people believe it is more ethical to experiment with invertebrates than vertebrates as they have less sophisticated nervous systems and may not feel pain in the same way 

• Care can be taken to minimise potential harm by

  • Animals should be handled gently

  • Examination periods should be kept as short as possible

  • Animals should be returned promptly to the holding tank after being examined

    • This is in line with ethical approaches that are appropriate to field work where pond animals are returned to their habitat after observations have been made

  • Extreme ranges of the variables being tested should be avoided, e.g. extremes of temperature or strong caffeine solutions