Video Transcript
An alveolus has a large surface
area relative to its volume. Which of the following best
describes the advantage of this? (A) A large surface area provides
more space for the enzyme-controlled reactions to take place. (B) A large surface area allows
temperature to be regulated more easily. (C) A large surface area prevents
the entry of microbes or pathogens. Or (D) a large surface area allows
more diffusion to occur.
This question asks us about the
structure of an alveolus. You might remember that alveoli,
the plural form of alveolus, are found in the lungs, which makes them part of the
respiratory system. The respiratory system has the very
important role of facilitating gas exchange, and the lungs are the major organ that
accomplishes this. After inhalation of air, oxygen
moves into the lungs.
Every cell in the body needs oxygen
for cellular respiration. The cardiovascular system, which
includes the heart and blood vessels, is responsible for picking up oxygen from the
lungs and delivering it to the entire body. When oxygen is used during cellular
respiration, carbon dioxide is produced as a waste product. This carbon dioxide is carried by
the cardiovascular system back to the lungs, where it can be exhaled.
You might be wondering how oxygen
and carbon dioxide move between the lungs and the cardiovascular system. Alveoli are small sac-like
structures. They are clustered at the ends of
bronchioles, which are divisions of the bronchi that carry air in and out of the
lungs. The exchange of gases between the
respiratory and cardiovascular systems occurs in the alveoli.
Alveoli are composed of very thin
epithelial tissue and are almost completely surrounded by capillaries, the thinnest
and smallest type of blood vessels. This close interaction between
capillaries and alveoli means that gases are easily exchanged between them in a
process known as diffusion. Oxygen moves into the
cardiovascular system, while carbon dioxide moves out.
We’re told that alveoli have a
large surface area relative to their volume. And we’ve learned that capillaries
interact with alveoli at their surface. A larger surface area would give
alveoli the advantage of more space to interact with capillaries, and therefore more
diffusion could occur. So we’ve shown that the correct
answer is choice (D). The large surface area of an
alveolus allows for more diffusion to occur.
