Composition of Atmosphere

The atmosphere is a mixture of gases that surrounds the Earth. It is composed of:

• Nitrogen (N2): About 78%
• Oxygen (O2): About 21%
• Argon (Ar): About 0.93%
• Carbon Dioxide (CO2): About 0.04%
• Trace gases: Including helium, neon, methane, krypton, and xenon
• Water vapor: Varies from 0% to 4%

Steps of Respiration

Respiration involves the following steps:

1. Breathing or Pulmonary Ventilation: The process of moving air into and out of the lungs.
2. External Respiration: The exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries.
3. Transport of Respiratory Gases: The transport of oxygen and carbon dioxide between the lungs and tissues through the bloodstream.
4. Internal Respiration: The exchange of gases between the blood in the systemic capillaries and the body’s cells.
5. Cellular Respiration: The process of using oxygen to produce energy (ATP) within cells and releasing carbon dioxide as a waste product.

Respiratory Organs in Different Animals

• Lower Animals:

  • Sponges: No specialized respiratory organs; gas exchange occurs through their surface.
  • Cnidarians (e.g., jellyfish): No specialized respiratory organs; gas exchange occurs through their body surface.
  • Annelids (e.g., earthworms): Skin or body surface acts as the respiratory organ.

• Higher Animals:

  • Fish: Gills are the primary respiratory organs.
  • Amphibians: Lungs and skin both play a role in respiration.
  • Reptiles, Birds, and Mammals: Lungs are the primary respiratory organs.

Lungs

• Structure: The lungs are a pair of spongy, air-filled organs located on either side of the chest (thorax).
• Function: The primary function of the lungs is to facilitate gas exchange between the air and the blood.
• Alveoli: The functional units of the lungs where oxygen and carbon dioxide are exchanged.
• Diaphragm: A dome-shaped muscle that plays a crucial role in breathing by contracting and relaxing to change the volume of the thoracic cavity.