Question

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Write a paragraph as if you are a molecule of carbon dioxide in the blood that will be excreted through the lungs. Start in the blood vessels of the lungs and finish as the breath is exhaled from the body.
Be sure to include what structures are involved, what other substances are involved, the path taken out of the body, and the effect on the body.

Answer 1

Carbon dioxide (chemical formula CO2) is a colorless and odorless gas that is vital to life on Earth. This naturally occurring chemical compound is made up of a carbon atom contently double bonded to two oxygen atoms. Carbon dioxide exists in Earth's atmosphere as a trace gas at a concentration of about 0.04 percent (400 ppm) by volume.Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and also in seawater. It is present in deposits of petroleum and natural gas.

Answer 2

Carbon dioxide is produced as waste product of cellular respiration in the body.

It is transported in the dissolved from in the blood.

It is transported by three mechanisms:

1. About 10% of carbon dioxide is transported in the dissolved form in the RBC.

At tissue level, the concentration of carbon dioxide is higher due to which it easily diffuses into the RBC and transported to the alveolar site.

2. Almost 20-30% is transported with the help of haemoglobin as carbamino-hemoglobin.

Hemoglobin can bind to both oxygen as well as carbon dioxide in a reversible manner depending on the partial pressure of both. Due to high partial pressure of carbon dioxide at tissue level, hemoglobin dissociates from oxygen and binds to carbon dioxide.

3. As bicarbonate ion: The carbon dioxide in RBC reacts with water and forms HCO₃⁻ & H⁺. The reaction is catalyzed by carbonic anhydrase.

At alveolar site, the reactions are reversed due to high partial pressure of oxygen and low partial pressure of carbon dioxide.

The dissolved carbon dioxide diffuse down the concentration gradient into alveolar site. Similarly, hemoglobin also dissociates from carbon dioxide and attaches with oxygen. Lastly, the same enzyme reverses the reaction and forms carbon dioxide and water from HCO₃⁻ & H⁺.