Carbon cycle

Step 3 - Activities

Which gas do we exhale?

With the following activity let’s seek answers for the following questions;

Which gases are exchanged in our body during respiration?
How do we prove that we exhale CO2?



In the setup described above, plants respire in the dark environment rather than performing photosynthesis. The CO2 accumulated in the test environment is transferred to another test tube via a glass capillary. Limewater is present in that tube.

Limewater is a good CO2 binding material. The color of the limewater changes slightly in comparison to its initial color when the CO2 collected in the first container is transferred into the second container.

Let’s consider a teacup. Let’s fill the cup with water halfway up and let’s slowly add tea on top. A color change similar to what would be observed is seen in the limewater as well. The limewater will change in proportion to the amount of CO2 gas. Thus, the color change in the limewater is in direct proportion to the amount of CO2.