Biology: Cellular Respiration and Gas Exchange

Aerobic Cellular Respiration

• Glucose reacts with oxygen to produce carbon dioxide and water, releasing energy
• Approximately 64% of the energy released is thermal energy
• About 36% is stored in ATP (adenosine triphosphate) molecules
• ATP powers cellular processes like growth, movement, and molecule building.
• ATP is formed from ADP (adenosine diphosphate) and a phosphate group through the addition of energy.

Gas Exchange and Ventilation

• Gas exchange is oxygen diffusion into cells and carbon dioxide diffusion out of cells.
• Simple organisms exchange gases directly across their cell membranes.
• Larger, multicellular organisms have organ systems to facilitate gas exchange between cells and the environment.
• Gas exchange occurs in lungs and cells.
• Lungs exchange oxygen from air into the blood, and carbon dioxide out of the blood and into the air.
• Cells receive oxygen from tissue fluid and release carbon dioxide to the bloodstream.
• Ventilation (breathing) moves air in and out of the lungs.

Respiratory Structures

• The human respiratory system has features like a thin, permeable, respiratory membrane, and large surface area for gas exchange with a good blood supply.
• The system ensures oxygen-rich air reaches the respiratory membrane in the lungs.
• The respiratory tract includes the nose, nasal passages, mouth, pharynx, trachea, bronchi, bronchioles, and alveoli.
• The trachea contains cartilage to maintain its shape, mucus-producing cells and cilia to trap and remove foreign materials.
• Alveoli are tiny sacs clustered in the lungs, essential for gas exchange, each with a high surface area surrounded by capillaries.

Gas Exchange in Alveoli

• Alveoli are filled with air at body temperature and humidity.
• Oxygen diffuses across the thin respiratory membrane into blood, only dissolved in the liquid components.
• The thin, one-cell-thick membrane is well-suited for efficient gas exchange.

Partial Pressures

• Air pressure varies with altitude.
• Partial pressure is the pressure exerted by individual gases in a mixture.
• Oxygen makes up approximately 20.9% of atmospheric air.
• Carbon dioxide is approximately 0.0391% of air.
• Partial pressures drive gas exchange.

Oxygen Transport and Diffusion

• The partial pressure of oxygen in the alveoli is higher than in the blood, so oxygen diffuses into the blood.
• Hemoglobin, an iron-containing protein, binds to oxygen forming oxyhemoglobin.
• Hemoglobin significantly enhances oxygen transport in the blood.
• At tissues, oxygen diffuses from the blood into cells.

Carbon Dioxide Transport and Diffusion

• Carbon dioxide is a cellular byproduct that must be removed.
• Carbon dioxide diffuses from cells into the blood.
• Some CO2 dissolves in plasma, some binds to hemoglobin, most is converted to bicarbonate ions.
• Bicarbonate and hydrogen ions are transported in blood to the lungs
• Pressure differences drive the diffusion of CO2 from the blood into the alveoli.

Altitude and Gas Exchange

• Atmospheric pressure and partial pressures decrease with altitude.
• Lower oxygen pressure at high altitudes leads to decreased gas exchange and oxygen supply, potentially causing altitude sickness.
• The body adapts by increasing red blood cell production to compensate for reduced oxygen availability.

Mechanism of Ventilation

• Inspiration: External intercostal muscles and diaphragm contract to increase thoracic cavity volume, decreasing lung pressure, allowing air to enter the lungs.
• Expiration: External intercostal muscles and diaphragm relax, decreasing thoracic cavity volume, increasing lung pressure, forcing air out of the lungs.

Lung Capacity

• Total Lung Capacity (TLC): Maximum air volume in lungs during inhalation.
• Tidal Volume (TV): Normal, involuntary breath volume.
• Inspiratory Reserve Volume (IRV): Air forcibly inhaled after tidal volume.
• Expiratory Reserve Volume (ERV): Air forcibly exhaled after tidal volume.
• Residual Volume (RV): Air remaining in lungs after forced exhalation (vital for preventing lung collapse).
• Vital Capacity (VC): Maximum air exhaled. (VC = TV + IRV + ERV)

This quiz covers key concepts of aerobic cellular respiration and gas exchange in living organisms. Learn how glucose and oxygen interact to produce energy and how organisms manage gas exchange through specialized systems. Test your understanding of ATP production and the mechanics of ventilation in lungs.