7.1.7 Practical - Investigating Respiration

• 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 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:
  • Exercise
  • 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 exercise on the heart rate of humans

Apparatus

• Heart rate monitor
• Stationary exercise bike (at a set resistance level)
• 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 exercise
• Ask each individual to cycle at a vigorous pace on the stationary exercise bike for a set period of time
  • It may be that the individuals are asked to maintain a particular RPM (revolutions per minute) while on the bike for 5 minutes
• After the five minutes of exercise is over, use the heart rate monitor to record the heart rates of each individual
  
  • 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 after exercise
• Present the results in a graph or table form

Limitations

• Care needs to be taken when selecting the exercise intensity
  • If the intensity is too low, it may not have an effect on the heart rate
  • If the intensity is too high, it could but the safety of individuals at risk
• 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 care would need to be taken to find individuals with a similar life history (same sex, age, weight and height etc.)

• We can investigate the production of carbon dioxide and heat from respiration through experiments using germinating seeds or other living organisms such as woodlice

Practical investigation: demonstrating the production of carbon dioxide

Apparatus

• Boiling tubes
• Rubber bungs
• Hydrogen carbonate indicator solution
• Cotton wool
• Glass beads
• Germinating seeds
• Boiled/dead seeds

Method

• Measure out 10 cm³ of hydrogencarbonate indicator into 3 boiling tubes
• Put in a layer of cotton wool
• Place 10 germinating seeds in tube A
• Place 10 boiled/dead seeds in tube B
• Place 10 glass beads in tube C
• Seal each tube with a rubber bung
• After 3 hours, observe the colour of the indicator

Hydrogencarbonate indicator

• Hydrogencarbonate indicator is orange in atmospheric CO₂ levels
• In high CO₂ levels the indicator absorbs the CO₂ and becomes yellow
• In low CO₂ levels it loses CO₂ and becomes purple

Colour results for hydrogen carbonate indicator

Results

• In this investigation, we would expect to note the following
  • Tube A should turn yellow as the seeds are respiring and producing carbon dioxide
  • Tube B should remain orange as the dead seeds produce no carbon dioxide
  • Tube C should remain orange as there is no living material in there

Experiment to demonstrate the production of carbon dioxide by living material during respiration

Practical investigation: demonstrating the production of heat

Apparatus

• Vacuum Flasks
• Thermometer
• Cotton wool
• Germinating seeds
• Dead/boiled seeds

Method

• Set up the flasks as shown in the diagram
  • Flask A with the germinating seeds
  • Flask B with the dead seeds
• Make sure the cotton wool is plugging the top of each flask
• Hold the thermometer in place with the cotton wool
• Invert the flask
• Record the initial temperature
• After 4 days, record the final temperature

Experiment to demonstrate the production of heat by living material during respiration

Results

• The thermometer in the flask with the germinating seeds (Flask B) should show an increase in temperature
• Flask A should remain at room temperature
• This is because the seeds in flask B are respiring and producing heat energy in the process
• This shows that respiration is an exothermic reaction
• The seeds in flask A are not respiring because they are dead, so the temperature remains the same