Q: Given the following data: Atmospheric pressure at sea level is $$760\ \mathrm{mm\ Hg}$$ and oxygen makes up $$21\% of $$the atmosphere. What is the partial pressure of oxygen ($$P_{O_2$}) at $$sea level?

$$P_{O_2$} = 0.21 \times 760 = 160\ \mathrm{mm\ Hg}$$

Question 1

Which of the following best explains why aquatic animals must expend more energy for gas exchange compared to terrestrial animals?

Accepted Answer

Water contains much less oxygen per liter than air and is both denser and more viscous, increasing the energy required for ventilation.

Question 2

Given the following data: Atmospheric pressure at sea level is $$760\ \mathrm{mm\ Hg}$$ and oxygen makes up $$21\% of $$the atmosphere. What is the partial pressure of oxygen ($$P_{O_2$}) at $$sea level?

Accepted Answer

$$P_{O_2$} = 0.21 	imes 760 = 160\ \mathrm{mm\ Hg}$$

Question 3

Why do fish gills utilize a countercurrent exchange mechanism?

Accepted Answer

To maintain a constant partial pressure gradient that favors the diffusion of $$O_2$$ from water to blood along the entire length of the capillary.

Question 4

Which adaptation is most critical for preventing the collapse of alveoli in mammalian lungs?

Accepted Answer

The production of surfactant, which reduces surface tension.

Question 5

A premature infant with a body mass less than $$1,200\ \mathrm{g} is at $$high risk for respiratory distress syndrome (RDS). Based on the data, what is the most likely physiological cause?

Accepted Answer

The infant's lungs have not produced enough surfactant to reduce alveolar surface tension.

Question 6

Which of the following statements about the tracheal system in insects is correct?

Accepted Answer

It consists of a network of air tubes that bring $$O_2$$ directly to body cells, largely independent of the circulatory system.

Question 7

Why is an internal location for gas exchange tissues advantageous for terrestrial animals?

Accepted Answer

It protects the moist respiratory surfaces from dehydration in a dry environment.

Question 8

After a heavy rain, earthworms are often seen on the surface. Which explanation best fits this behavior in terms of gas exchange?

Accepted Answer

Earthworms require oxygen from the air because waterlogged soil contains less available $$O_2$$ for diffusion across their skin.

Question 9

Which of the following best describes the relationship between surface area and diffusion rate across a respiratory surface?

Accepted Answer

The rate of diffusion is proportional to the surface area and inversely proportional to the square of the diffusion distance.

Question 10

A fish is swimming in water with a $$P_{O_2$} of$$ $$120\ \mathrm{mm\ Hg}. If $$the $$P_{O_2$} in $$the fish's blood entering the gills is $$110\ \mathrm{mm\ Hg}$$, in which direction will net diffusion of $$O_2$$ occur?

Accepted Answer

From water to blood

Question 11

Which of the following is NOT a characteristic of respiratory surfaces?

Accepted Answer

They are always located on the external surface of the body.

Question 12

Which of the following best explains why mammals are more susceptible to lung damage from inhaled particulates than from gases?

Accepted Answer

Alveoli lack cilia and significant air currents to remove particles, making them vulnerable to contamination.

Question 13

Which of the following is a direct consequence of the countercurrent exchange system in fish gills?

Accepted Answer

A partial pressure gradient for $$O_2 is $$maintained along the entire length of the gill capillary.

Question 14

Which of the following would most likely increase the rate of $$O_2$$ diffusion across a respiratory surface?

Accepted Answer

Increasing the partial pressure gradient of $$O_2$$ across the surface

Question 15

Which of the following is a correct comparison between air and water as respiratory media?

Accepted Answer

Air is less dense and less viscous than water, making it easier to move through respiratory passageways.

Question 16

Which structure in the mammalian respiratory system is primarily responsible for gas exchange?

Accepted Answer

Alveoli

Question 17

If a mutation caused a mammal to produce no surfactant, what would be the most likely physiological consequence?

Accepted Answer

The alveoli would collapse due to increased surface tension, severely impairing gas exchange.

Question 18

Which of the following best describes the function of the 'mucus escalator' in the mammalian respiratory system?

Accepted Answer

It traps and removes particulate contaminants from the respiratory tract.

Question 19

Which of the following is a similarity between countercurrent exchange in fish gills and in the legs of geese?

Accepted Answer

Both systems maintain a gradient that allows for efficient transfer (of $$O_2 in $$gills, and heat in geese) along the entire length of the exchange surface.

Gas Exchange Across Specialized Respiratory Surfaces

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