Microbiome respiration demonstration

Download PDF here

Soils contain a huge number of organisms. You may have explored those we can see (eg. worms and springtails), there even more single-celled organisms such as bacteria and protozoas. These organisms are the main agents in nutrient cycling in soils and their impact on the carbon cycle can be demonstrated, but not instantly.

Specific learning outcomes

  • Gain understanding of microscopic soil community/organisms
  • Increased understanding of nutrient cycling within soil
  • Understanding of the role of microorganisms in decay
  • Knowledge of the process of respiration of of microbes

Equipment for a group of 5

  • 1 jar with airtight lid
  • Soil from garden
  • Sugar
  • Compost
  • Plastic bottle
  • Water
  • Lime water


Estimated time 5-10 minutes.

  • Soil sample
  • Preparing weak sugar solution (approximately 5g sugar:100ml water)


Introduction to activity, ~3 mins
Construct soil chamber and insert limewater ~5 mins
Activity total timing ~10 minutes.
Evidence of microbial respiration will be viewable within 2-7 days.

Background learning needs

  • Understanding of microbes – desirable
  • Understanding of carbon cycle – desirable
  • Understanding of respiration of bacteria


  1. Ensure the soil is broken up into a crumb, fill the jar to approximately ⅔’s full
  2. Cut the top ~7cm off the top of a 500ml drinks bottle and screw cap on firmly
  3. Push the capped end of the bottle firmly into the soil, leaving ~3cm exposed above the surface of the soil
  4. Water the soil with the sugar water, so that it is damp throughout but not pooling
  5. Add the lime water to the bottle top, fill up to 1cm above the soil surface, so it is visible above the soil
  6. Close the jar and place in a dark and warm environment.
  7. Check the soil jar on a daily basis to see if the colour of the limewater alters and when this is. Increasing cloudy colouring of the limewater will show the presence of CO2 in the jars air.

Potential extension

Water the soil until it is waterlogged and repeat the exercise this will show, to an extent, if the soil produces CO2 at a slower or faster rate when in anaerobic conditions.