Edexcel A (SNAB) A Level Biology:复习笔记1.1.6 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


  • Light microscope
  • Cavity slide
  • Culture of Daphnia
  • Pipette
  • Caffeine solutions at a range of concentrations
  • Distilled water
  • Stop watch


  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


  • You can also investigate the effect of
    • Temperature
    • Other chemicals such as alcohol (1% ethanol solution)


  • 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