Investigating Heart Rate (AQA A Level Biology)

Apparatus & Techniques: Investing Factors Affecting 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 (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.)