describe the structure, function, and interactions of the organs of the human respiratory systems

Respiration is the release of Energy from Food using Oxygen

Food + Oxygen → Energy + Carbon Dioxide + Water Vapour

To demonstrate why our trachea needs cartlige to keep it open

  • take 2 sheets of paper (or balloons)
  • hold them a few centimeters apart
  • blow through the gap (or use a hairdryer)
  • What do you expect
  • observe the gap between the sheets

When air passes through a narrow place the pressure decreases which means that the tube will normally collapse.


Rings of cartilage are needed to keep the wind pipe open.

The products of respiration

To test for Carbon Dioxide


Limewater, Test-Tubes (or conical flasks), Bungs (corks), Glass tubes & drinking straws,


  1. Half fill test-tube with (clear) Limewater
  2. Put in 2 glasstube bung
  3. Decide if you will Inhale or exhale, your partner should do the opposite.
  4. By exhaling or inhaling bubble gas through the limewater for a set number of breaths
  5. Compare with your partner the colour of the limewater


The tube through which we exhaled was Cloudy / Milky

The tube through which we inhaled was left clear


Lime water goes Milky when in contact with Carbon Dioxide CO2

Therefore exhaled breath has MORE carbon Dioxide than Inhaled air

To test for Water Vapour from your breath


Cold Tile, Anhydrous Copper Sulphate Powder (white)


  1. Remove tiles from fridge after spending time there overnight
  2. Exhale / Breath on cold tile
  3. Sprinkle copper sulphate powder on the tile
  4. Observe any changes



The Anhydrous Copper Sulphate Powder went blue in colour

Copper Sulphate Powder is blue when in contact with water


The water vapour from our breath condensed on the cold tile.

We produce water vapour when we respire


Cobalt Chloride can also be used to test for water vapour, however these test papers are hard to use when they get old. Also these papers are banned in Irish Schools

Blue Cobalt Chloride Paper goes Pink in the presence of water