Respiration and Gas Exchange Concepts

Respiration

• Respiration is a set of metabolic reactions in cells that convert biochemical energy from nutrients into ATP (chemical energy).
• Respiration supplies oxygen for cellular respiration and disposes of carbon dioxide.
• Different organisms use various strategies for respiration, which depends on their environment.
• The general function is to get oxygen to cells and remove carbon dioxide.

Gas Exchange

• Gas exchange is necessary to supply oxygen and dispose of carbon dioxide for cellular respiration.
• Respiratory medium (air or water) is involved in the exchange process, alongside respiratory surfaces.
• The circulatory system transports gases.
• Cellular respiration produces ATP using energy-rich molecules from food.
• This process involves breathing, and the transport of oxygen and carbon dioxide.

General Concepts

• Specialized organs for respiration have extensive structures (invaginations and evaginations) to increase membrane surface area to facilitate gas exchange.
• Gills are outpouchings (evaginations) and lungs are invaginations.
• Respiratory organs include lungs, external gills and internal gills.
• Adjectives used to describe them include branchial for gills and pulmonary for lungs.

Respiratory Organs

• Diagrams show respiratory organs in various organisms: flatworm, fish, terrestrial arthropod, and mammals.
• Flatworms exchange gases through body walls.
• Fish use gills for gas exchange.
• Terrestrial arthropods use tracheae.
• Mammals use lungs with alveoli for gas exchange.

Protozoa Respiration

• Single-celled organisms like Amoeba and Paramecium exchange gases through the plasma membrane by simple diffusion.

Small Invertebrates (e.g., Flatworm)

• Diffusion is effective for gas exchange in flatworms due to their small size.
• Their flat shape maximises surface area to volume ratio.
• Gases move across their body wall by diffusion.

Bird Respiration

• Bird lungs are rigid, with little change in volume.
• Air sacs expand and contract.
• Air flows unidirectionally through the lungs.
• The gas exchange system is cross-current.

Mammalian Lungs

• Mammalian lungs are densely filled with branching airways and contain alveoli (approximately 300 million) in humans.
• The gas exchange membrane has a massive surface area compared to the size of the lung.
• The surface area of a human lung is roughly equal to a tennis court.
• The thickness of the barrier between blood and air is just 2 layers of cells.
• Blood vessels surround alveoli.

Mammalian Respiration

• Air moves through the nose, pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli for gas exchange.
• The diaphragm and thoracic muscles facilitate the movement of air in and out of the lungs during inhalation and exhalation.
• The amount of air exchanged in breathing is described by tidal volume, residual volume, and vital capacity.

Respiratory Pigments

• Respiratory pigments are essential for binding and transporting gases, as oxygen has low solubility in water.
• Haemoglobin (containing iron) is the main pigment in vertebrates, found in red blood cells.
• Haemocyanin (containing copper) is the respiratory pigment in arthropods and many molluscs.

Oxygen Transport

• Haemoglobin reversibly binds oxygen, loading it in the lungs and unloading it in other body parts (lower partial pressure).
• The oxygen loading and unloading process facilitates efficient gas transport throughout the body.

Revision Questions

• What are the principles of countercurrent exchange?
• Name two respiratory pigments.
• Describe Tidal Volume, Residual Volume, and Tidal Capacity in humans.
• What does the oxygen molecule bind to in the haemoglobin molecule?