• 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 (water fleas /?Daphnia) as well as vertebrates (humans)
  • Serious 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
  • Weight
  • Height
  • Temperature
  • Diet
  • Dehydration

   

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

Investigating the effect of caffeine on the heart rate of humans

Apparatus

• Heart rate monitor
• Caffeine solution of a known concentration
• Measuring cylinders
• Cups
• One group of healthy humans

Method

• Use the heart rate monitor to record the heart rates of each individual while at rest
  • These results can be used to calculate the mean heart rate of the group as well as the range of resting heart rates for the group prior to caffeine consumption

   

• Use the measuring cylinder to pour 200ml of the caffeine solution into a cup (one for each individual)
• Ask each individual to consume the drink
• Wait 15 minutes
• Use the heart rate monitor to record the heart rates of each individual while at rest
  • These results can be used to calculate the mean heart rate of the group as well as the range of resting heart rates for the group after caffeine consumption
  • It is important that the individuals taking part are not moving and all sat down so that these variables are controlled

   

• Repeat the heart rate measurements every 15 minutes for 2 hours
  • This will show the duration for which caffeine has an effect on the heart rate

   

• Present the results in a graph or table form

Limitations

• Care needs to be taken when selecting the caffeine concentration
  • Too much caffeine can be dangerous, while too little may show no effect

   

• It is very difficult to ensure that individuals within a sample group are sufficiently similar
  • By using the same group for the before and after measurements this is not as much of an issue
  • If multiple groups were used, with some consuming caffeine and some not, then this would be a major issue and care would need to be taken to find individuals with a similar life history (same sex, age, weight and height etc.)