We inhale air but oxygen is filtered out of the mixture if all gases. But I think the answer would be oxygen because they are asking specifically 'which gas..'

Inhaling Oxygen: The Essential Gas for Living Organisms

Living organisms require a constant supply of oxygen to survive. Oxygen is an essential element that enables the process of respiration, allowing organisms to produce energy for their various biological functions. Let's explore in detail the significance of oxygen and how living organisms inhale this vital gas.

1. Importance of Oxygen:

Oxygen plays a crucial role in the process of cellular respiration. It acts as the final electron acceptor in the electron transport chain, a series of reactions that occur within the mitochondria of cells. This process generates adenosine triphosphate (ATP), the main energy currency of cells. Without oxygen, the production of ATP significantly decreases, leading to cellular dysfunction and, ultimately, the organism's death.

2. The Respiratory System:

The respiratory system is responsible for the inhalation of oxygen and the exhalation of carbon dioxide, a waste product of cellular respiration. The process of respiration involves several organs and tissues, including the nasal cavity, trachea, bronchi, and lungs.

3. Inhalation of Oxygen:

When an organism inhales, the diaphragm and intercostal muscles contract, causing the volume of the thoracic cavity to expand. This expansion decreases the air pressure within the lungs, creating a pressure gradient between the outside air and the alveoli (tiny air sacs within the lungs). As a result, air rushes into the respiratory system, carrying oxygen molecules.

4. Gas Exchange in Alveoli:

Once the inhaled air reaches the alveoli, gas exchange occurs. The thin walls of the alveoli allow oxygen molecules to diffuse across into the bloodstream, where they bind to hemoglobin molecules found within red blood cells. Hemoglobin then transports the oxygen-rich blood to the body's tissues, ensuring the delivery of oxygen to every cell.

5. Exhalation of Carbon Dioxide:

Conversely, during exhalation, the diaphragm and intercostal muscles relax, reducing the volume of the thoracic cavity. This contraction increases the air pressure within the lungs, causing the expulsion of air and the removal of carbon dioxide, which is a waste product of cellular respiration.

Conclusion:

Inhaling oxygen is a vital process for living organisms as it allows for the production of energy through cellular respiration. The respiratory system facilitates the intake of oxygen and the removal of carbon dioxide, ensuring the oxygenation of body tissues. Understanding the significance of oxygen and how organisms inhale this gas provides valuable insights into the fundamental processes necessary for life.