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7.4 Ventilation and Gas Exchange in Other Organisms

Blood Flow in Gills

• Blood leaves the gills after oxygen has been absorbed, reaching equilibrium when the oxygen concentration in blood and water is equal, resulting in no further net diffusion.

• Countercurrent System: Blood and water flow in opposite directions, maintaining a steep oxygen gradient across the gills, allowing maximum absorption of oxygen into the blood. The design allows fish to extract approximately 80% of oxygen from water compared to approximately 50% by cartilaginous fish that use a parallel system.

Structure of Gills in Bony Fish

• Gills are delicate structures with a large surface area and rich blood supply.

• Significant structures include:

  • Gill lamellae: primary sites for gas exchange due to their extensive surface area.

  • Operculum: protective flap covering the gills, aiding in water flow and pressure maintenance.

Dissection for Understanding Gas Exchange Systems

• Provides clarity on internal systems of organisms and their evolutionary adaptations.

• Essential tools for dissection include:

  • Sharp scissors, scalpels, tweezers, and mounted needles for precise cuts and observations.

• Aim for clear, well-labelled diagrams, possibly supplemented with photographs for reference.

Observations From Dissection

1. Drawings should be in pencil for clarity.

2. Record features observed during dissection of gas exchange systems in organisms like insects and bony fish.

Example Structures

• Insect Trachea: Chitin rings support the trachea for gas diffusion; air can diffuse freely due to absence of chitin at tracheole ends.

• Tracheoles extend throughout tissues, providing extensive gas exchange surface. Oxygen dissolves in the moisture within tracheoles before diffusing into cells. Increased oxygen demand during activities like flight leads to water moving out of tracheoles, enhancing surface area exposure for gas exchange.

Discontinuous Gas Exchange Cycles (DGC) in Insects

• Spiracles regulate gas exchange, having three states: closed, open, and fluttering.

• Closed: Prevents gas movement, allowing for diffusion from tracheae into cells.

• Fluttering: Allows some fresh air in, maintaining oxygen levels while reducing water loss.

• High carbon dioxide levels lead to wide opening of spiracles for rapid gas exchange. DGC is thought to adaptively reduce water loss and possibly protect against fungal spores.

Challenges for Aquatic Animals

• Aquatic animals face unique challenges due to water density, viscosity, and lower oxygen content.

• Evolved specialized respiratory systems to manage these challenges more effectively than lung-like structures in land animals.

Features of Gills

• Adaptations for Gas Exchange:

  • Extensive surface area, thin membranes for short diffusion distances, rich blood supply to enhance gradients.

  • Continuous flow of water ensures constant oxygen availability and carbon dioxide removal, crucial for active fish like trout.

Investigating Gas Exchange Systems

• Effective observational methods include dissecting organisms and preparing microscope slides to explore histology of exchange surfaces in various organisms.

Importance of Study Tips

• Recognizing key features of efficient gas exchange surfaces and their adaptations provides a foundation for understanding the physiological adaptations of various organisms engaged in gass exchange.