Experiment 12 — What Is in the Air You Breathe Out?

Topic: Biology · Classes 6–7 · Respiration in living organisms

Aim: Turn the lime water milky , and prove where the carbon dioxide came from.

Daily: Every living thing — you, a sleeping dog, a germinating seed, even the yeast in bread dough — respires and releases carbon dioxide. This simple milky test is how a laboratory detects that gas.

Question: Air from a jar of germinating seeds is bubbled through lime water. What happens?

Exp: Germinating seeds respire actively and release carbon dioxide, even though they have no lungs.

Question: Lime water turning milky shows the presence of…

Exp: It is the standard test for CO₂.

Question: Exhaled air contains about…

Exp: Roughly a hundred times more than ordinary air.

Exp: Breathing merely moves the air; respiration is the chemical process.

Question: Boiled seeds do not turn lime water milky because they…

Exp: That control proves respiration is a sign of life.