Gas exchange: Surface area and organisms

• Gas exchange involves oxygen intake into cells and the release of carbon dioxide
• It is essential for providing oxygen for cellular respiration, which produces ATP energy for survival
• The gas exchange surface is where gases enter (oxygen) and exit (carbon dioxide)

Surface Area Importance

• A large surface area is essential for maximizing oxygen diffusion into the organism and carbon dioxide expulsion
• Mammals, fish, and insects have developed specialized structures to maximize surface area for gas exchange

Mammals

• Have lungs with alveoli which are tiny air sacs which provide a large surface area for gas exchange
• Alveoli enhance oxygen absorption and carbon dioxide expulsion because of thin walls

Fish

• Have gills containing thin filaments covered in lamellae, increasing surface area for oxygen absorption
• Water flows over gills allowing oxygen to diffuse into the blood while carbon dioxide diffuses out

Insects

• Rely on a tracheal system, a network of branching tubes for direct air delivery to tissues
• Tracheal systems increase surface area for gas diffusion and eliminate the need for a circulatory system in smaller organisms
• Structures are specifically suited to each animal's environment
• Mammals have alveoli that are well suited for air environments, fish use gills for extracting oxygen from water, and insects use a tracheal system tailored for direct gas delivery

Support Structures

• Support structures are important in maintaining the gas exchange system's functionality and integrity for effective gas exchange
• For efficiency and prevention of system collapse, maintenance of airflow or water flow are all important

Mammals

• Lungs are supported by the diaphragm and rib cage, which facilitates lung expansion and contraction during breathing
• The diaphragm's movement draws air into the lungs, while the rib cage protects the lungs and ensures their proper positioning

Fish

• Have gill arches that support gill filaments and ensure proper water flow crucial for maintaining a concentration gradient

Insects

• Benefit from a tracheal system supported by chitin rings that prevent tracheal tubes from collapsing and ensure free air flow to the tissues

Evaluation: Mammals

• The alveoli provide a large surface area for oxygen absorption and carbon dioxide expulsion
• System supports the high metabolic demands of mammals, enabling activities that require much energy
• The system is limited to air environments as alveoli cannot function properly in water
• Mammals stay terrestrial or evolve to hold their breath in aquatic environments using marine adaptations

Evaluation: Fish

• Gills utilize a countercurrent exchange system to ensure efficient oxygen absorption, even in low-oxygen water
• Allows fish to effectively extract oxygen from their environment compared to simple diffusion
• A limitation is that fish depend on water for oxygen exchange, making gills ineffective in air
• Lungfish can breathe air and survive in oxygen-depleted waters or variable environments

Evaluation: Insects

• Tracheal system ensures direct oxygen delivery to tissues in smaller organisms
• Eliminates the circulatory system needed to transport gas, allowing for rapid oxygen diffusion through tissue
• Less effective for larger organisms because of the increase in distance for diffusion
• Insects remain small and optimize gas exchange by increasing the branching of tracheal tubes, but this limits their efficiency