Activity 6.1: Comparing Breathing Rates

Aim/Objective: To observe and compare the variation in human breathing rates during different levels of physical activity.

Materials Required:

• A stopwatch or a watch with a second hand.
• Participants (friends or classmates).

Procedure:

1. Sit comfortably and count the number of times you breathe in and out (one breath = one inhalation + one exhalation) in one minute. This is your resting breathing rate.
2. Walk for 10 minutes at a moderate pace and immediately count your breathing rate for one minute.
3. Run for 2–3 minutes as fast as you can and count your breathing rate immediately after stopping.
4. Record your breathing rates and compare them with your classmates' data.

Observation:

• The breathing rate is lowest when at rest.
• The breathing rate increases significantly during and immediately after walking and running.
• After heavy exercise, the breathing rate is much higher than the resting rate.

Explanation:

• Respiration is the process of breaking down food (glucose) to release energy. This process requires oxygen.
• During physical activities like running or walking, our body's muscles require more energy.
• To meet this increased energy demand, the body needs more oxygen to fuel cellular respiration.
• The brain signals the respiratory muscles (diaphragm and intercostal muscles) to contract and relax faster, thereby increasing the breathing rate to deliver more oxygen to the blood and eventually to the cells.
• Higher breathing rate also helps in removing the excess carbon dioxide produced during intense muscular activity.

Conclusion:

• The breathing rate of a person increases with an increase in physical activity to meet the heightened demand for energy and oxygen.

Activity 6.2: Testing for Carbon Dioxide in Exhaled Air

Aim/Objective: To demonstrate that carbon dioxide is present in the air we exhale.

Materials Required:

• A clean test tube.
• Freshly prepared lime water (Calcium hydroxide solution).
• A plastic straw or a glass tube.

Procedure:

1. Pour a small amount (5–10 mL) of freshly prepared lime water into the test tube.
2. Insert a straw into the lime water.
3. Gently blow air into the straw for a minute or two.
4. Observe any change in the appearance of the lime water.

Observation:

• The clear lime water turns milky (turbid) when exhaled air is blown into it.

Explanation:

• Lime water is a solution of calcium hydroxide [Ca(OH)2].
• When carbon dioxide (CO2) reacts with calcium hydroxide, it forms an insoluble white precipitate of calcium carbonate (CaCO3).
• The chemical equation for this reaction is: Ca(OH)2 + CO2 → CaCO3 + H2O.
• The appearance of this white precipitate makes the solution look milky.
• This reaction is a standard chemical test for the presence of carbon dioxide.
• Our cells produce CO2 as a byproduct of aerobic respiration, which is then transported to the lungs and exhaled.

Conclusion:

• Exhaled air contains a significant amount of carbon dioxide, which is a byproduct of cellular respiration.