Problem 10 - Campbell Biology Concepts & Connections

Question

What are two advantages of breathing air, compared with obtaining dissolved oxygen from water? What is a comparative disadvantage of breathing air?

Step-by-Step Solution

Answer

Air has higher oxygen concentration and is easier to move than water, but risks causing drying out.

Step 1 - Identify the advantages of breathing air.

Breathing air has two main advantages over obtaining dissolved oxygen from water. Firstly, the concentration of oxygen in air is much higher than in water. Secondly, air is less dense and less viscous than water, making it easier to move in and out of the respiratory structures.

Step 2 - Discuss the concentration of oxygen.

Air contains approximately 21% oxygen, while water usually contains much less oxygen, often less than 1%. This high concentration of oxygen in the air allows for more efficient gas exchange in the respiratory system.

Step 3 - Explain the movement of the medium.

Since air is less dense and less viscous than water, it requires less energy to ventilate the respiratory surface. Animals that breathe air tend to have more efficient breathing mechanisms than those that extract oxygen from water.

Step 4 - Identify a disadvantage of breathing air.

A comparative disadvantage of breathing air is the risk of desiccation (drying out). Respiratory surfaces that are exposed to air can lose moisture quickly, leading to dehydration if not managed properly.

Key Concepts

Oxygen Concentration

One key advantage of breathing air over water is the higher concentration of oxygen. Typically, air contains about 21% oxygen. In contrast, water often has less than 1% oxygen.
This difference in oxygen levels plays a crucial role in gas exchange processes.
Organisms that breathe air can obtain oxygen more efficiently due to the greater availability. This efficiency is pivotal for sustaining metabolic activities and overall health.
Land animals benefit significantly from this high oxygen concentration, allowing their bodies to function optimally.

Gas Exchange Efficiency

The efficiency of gas exchange is another key point to consider. Because air contains much more oxygen than water, animals breathing air can achieve gas exchange with less effort.
Less energy is required to move air in and out of lungs compared to moving water through gills. This efficiency means that animals can sustain higher levels of activity due to the more accessible oxygen.
Being able to extract oxygen more efficiently allows for faster and more effective respiratory processes, leading to better overall organism health.

Ventilation Effort

Ventilation effort is significantly reduced when breathing air compared to water. Air is less dense and less viscous than water, making it easier to inhale and exhale.
This reduced resistance translates to less energy expenditure. For land animals, this means that they can focus their energy on other survival activities, such as foraging and escaping predators.
Overall, the lower ventilation effort required by air breathers provides an improved respiratory efficiency, enabling better adaptation to their environments.

Risk of Desiccation

A notable disadvantage of breathing air is the risk of desiccation, or drying out. Respiratory surfaces, such as lungs, need to remain moist for effective gas exchange.
When exposed to air, these surfaces can lose moisture quickly due to evaporation. This can lead to dehydration if not effectively managed.
Animals have developed several adaptations, like mucous membranes and behaviors like seeking shade, to combat desiccation.
However, the constant threat of losing vital moisture remains a challenge, necessitating a balance between efficient respiration and hydration.