Problem 13 - Campbell Biology

Question

The diving bell spider (Argyroneta aquatica) stores alr underwater in a net of silk. Explain why this adaptation could be more advantageous than having gills, taking into account differences in gas exchange media and gas exchange organs among anlmals.

Step-by-Step Solution

Answer

The diving bell spider's air storage allows it to utilize the higher oxygen concentration in air, conserving energy compared to using gills.

Step 1: Identify the Adaptation

The diving bell spider (Argyroneta aquatica) stores air underwater in a silk net. This allows the spider to breathe while submerged.

Step 2: Understand Gills and Their Function

Gills are specialized organs used by many aquatic animals to extract oxygen from water. They have a large surface area to facilitate gas exchange.

Step 3: Compare Gas Exchange Media

Water contains less oxygen compared to air. Extracting oxygen from water through gills requires more energy and efficiency in the exchange process.

Step 4: Analyze the Advantages of Storing Air

Storing air underwater allows the spider to take advantage of the higher oxygen concentration in air. This reduces the energy required for gas exchange compared to using gills.

Step 5: Consider the Versatility of Air Storage

Storing air in a silk net allows the spider to remain underwater for extended periods without needing to frequently surface for oxygen. This could provide a survival advantage by keeping the spider hidden from predators and allowing it to hunt.

Step 6: Conclude the Comparison

Overall, storing air underwater in a silk net is more advantageous for the diving bell spider than having gills. This adaptation leverages the higher oxygen concentration in air and allows the spider to conserve energy while submerged.

Key Concepts

Gas Exchange

Gas exchange is a vital process for all living organisms, allowing them to obtain the oxygen needed for survival and release carbon dioxide as a waste product.
In aquatic animals, this process can be a bit tricky because water contains less oxygen than air. However, they have developed various methods to efficiently extract the oxygen they need.

In general, gas exchange involves the movement of gases across a membrane. Oxygen moves into the organism while carbon dioxide moves out. This process is driven by the concentration gradients of the gases and the surface area available for exchange.

Gills vs Air Storage

Many aquatic animals like fish use gills for gas exchange. Gills are specialized organs designed with a large surface area to maximize the amount of oxygen that can be absorbed from the water.
However, extracting oxygen from water is energy-intensive because of the low oxygen concentration in water compared to air.

On the other hand, the diving bell spider uses a silk net to store air underwater. This adaptation allows the spider to take advantage of the higher oxygen concentration in air.

• Gills:
• Large surface area
• Efficient gas exchange but energy-intensive due to low oxygen in water
• Air Storage:
• Uses air with higher oxygen concentration
• Less energy needed for gas exchange

Adaptations in Aquatic Animals

Aquatic animals have evolved numerous adaptations to survive in their watery environment, with gas exchange being a primary focus.
While many rely on gills, others, like the diving bell spider, have developed unique strategies.

The diving bell spider constructs a net of silk to trap air, which it then uses for breathing while submerged. This adaptation provides several advantages:

• Conserves Energy:
• Utilizes the higher oxygen concentration in air, reducing the energy required for gas exchange
• Increases Underwater Time:
• Allows the spider to stay submerged longer without needing to surface for air
• Improves Survival:
• Staying underwater for extended periods helps avoid predators and improves hunting efficiency.

Oxygen Concentration in Water and Air

Oxygen concentration varies significantly between water and air, impacting how organisms conduct gas exchange.
Air contains about 21% oxygen, while water typically has only a tiny fraction of that amount. This disparity means that extracting oxygen from water requires specialized adaptations.

Aquatic animals with gills must process large volumes of water to obtain sufficient oxygen. This is not as efficient as utilizing air, where oxygen is more readily available.

• Air:
• High oxygen concentration (21%)
• Energy-efficient for gas exchange
• Water:
• Low oxygen concentration
• Requires more energy for extraction

In summary, the diving bell spider's air storage adaptation is advantageous because it utilizes the higher oxygen concentration in air, allowing the spider to save energy and stay submerged longer.