Practical: Investigating Respiration (Edexcel IGCSE Biology)

Practical: Investigating Respiration

• 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 red in atmospheric CO₂ levels

  • In high CO₂ levels the indicator reacts to CO₂ dissolving in water, which forms carbonic acid and changes the pH, causing it to become yellow

  • In low CO₂ levels the lack of CO₂ makes the solution more alkaline, causing the colour to shift to 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 red as the dead seeds produce no carbon dioxide

  • Tube C should remain red 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 dead seeds

  • Flask B with the germinating 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

Applying CORMS evaluation to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• In the first investigation, your evaluation should look something like this:

  • Change - We will change the content of the boiling tube (germinating seeds, dead seeds or glass beads)

  • Organisms - The seeds used should all be of the same age, size and species

  • Repeat - We will repeat the investigation several times to ensure our results are reliable

  • Measurement 1 - We will observe the change in the hydrogen carbonate indicator

  • Measurement 2 - ...after 3 hours

  • Same - We will control the volume of hydrogen carbonate indicator, the number of seeds/beads, the temperature of the environment

• For the second investigation, your evaluation should look something like this:

  • Change - We will change the content of the flasks (germinating seeds or dead seeds)

  • Organisms - The seeds used should all be of the same age, size and species

  • Repeat - We will repeat the investigation several times to ensure our results are reliable

  • Measurement 1 - We will observe the change in the temperature on the thermometer

  • Measurement 2 - ...after 4 days

  • Same - We will control the number of seeds, the starting temperature of the flasks, the material and size of the flasks