Activity 6 Exhaled Air

[Pages:3]Exhaled air

Name

Date

Breathing is the process that takes air in and then takes carbon dioxide and other gases out of the body. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose.

Breathing is only part of the processes that deliver oxygen to where it is needed in the body and remove carbon dioxide. The process of gas exchange occurs in the alveoli by passive diffusion of gases between the alveolar gas and the blood passing by in the lung capillaries. Once these dissolved gases are in the blood, the heart powers their flow around the body (via the circulatory system).

In addition to removing carbon dioxide, breathing results in loss of water from the body. Exhaled air has a relative humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli.

The air we breathe in is 21% O2 and 79% N2, (neglecting humidity). When the air reaches the lungs, some of this oxygen is transferred from the lungs to the blood, and is then transported throughout the body to be used for energy. In addition, the blood contains some carbon dioxide (a waste product) that is transferred to the air in the lungs, which is then exhaled. The result is that the exhaled air contains less oxygen and more carbon dioxide than the inhaled air.

The air in the lungs also becomes humidified with water before it is exhaled. In fact, exhaled air is completely saturated with water ? it contains the maximum amount of moisture, and is therefore has a relative humidity of 100%. We lose water as we breathe! The typical composition of exhaled air is about 18% O2, 78% N2, and 4.0% CO2.

Gas

Nitrogen Oxygen Carbon dioxide Other gases

Atmospheric air % 79 21 0.04 1

Exhaled air % 78 16 4 1

*The percentage of a gas in a mixture can vary, even if the actual amount of the gas stays the same.

With each breath, approximately 0.5 L of air travels deep into the lungs, into tiny sponge-like sacs called alveoli, where the exchange of oxygen, carbon dioxide, and water between the air and the body occurs. A typical rate of breathing (at rest) is about 12-20 breaths per minute.

Lime water can be used to measure the amount of exhaled gas

Materials

2 sets of apparatus as seen in figure 1 graduated cylinder (10 cm3)

rack for holding boiling tubes

spirit marker

Procedures

1. You are provided with two large boiling-tubes fitted with rubber

bungs and delivery tubes as shown in the Figure and also two

lengths of rubber tubing.

2. Label the tubes A and B. 3. Use a graduated cylinder to place 10 cm3 lime water in each test-

tube.

4. Place the bungs in both tubes and connect one length of rubber

tubing to each test-tube as follows: with tube A fit the rubber tubing A

B

to the shorter glass tube, with tube B fit the rubber tubing to the

longer glass tube (see Figure).

5. Put the ends of both rubber tubes at the same time in your mouth and breathe in and out

through the tubes for about 15 seconds. Notice which tube is bubbling when you breathe out

and which one bubbles when you breathe in.

6. Compare the lime water in each tube. If there is no difference, breathe in and out through the

tubes for another 15 seconds. 7. Repeat the experiment using 10 cm3 distilled water and 5 drops of Universal Indicator.

Discussion

1. Where did the air passing through test-tube A come from? Where did the air passing through test-tube B come from?

2. What difference was there in the appearance of the lime water in the two tubes ?

3. Which gas turns lime water milky?

4. What do the results tell you about the composition of the air you breathe out and the air you breathe in?

5. Why was it necessary to include tube A when results could have been obtained simply by breathing out through the lime water in B?

6. Explain your results using the Universal Indicator.

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download