Video Transcript
How are the majority of waste
materials removed from the digestive system? (A) By excretion, (B) via
respiration, (C) through reabsorption in the large intestine, (D) as urine, or (E)
as feces.
In order to understand how to
answer this question, let’s see what some of the key terms that have been used in
the answer options mean. Excretion is a process that occurs
in almost every single body cell, in which the waste products of their metabolic
reactions are removed. These waste products might, for
example, be carbon dioxide, which is produced in cellular respiration in muscle
cells and needs to be removed from them.
A common misconception is that
excretion and egestion are the same thing. This is not the case, however. While excretion removes metabolic
waste products formed by cells, egestion refers to the final removal of undigested
waste products from the large intestine, which occurs via a process called
defecation. Therefore, we can deduce that
excretion is not how the majority of waste products are removed from the digestive
system.
Cellular respiration is a process
that occurs in cells by which carbon-containing compounds, like glucose, are broken
down to release energy. Though we’ve already learned that
the carbon dioxide produced in cellular respiration will be excreted from cells, we
know that excretion is not the same as egestion. So, this answer must also be
incorrect.
The main function of the large
intestine is to absorb water and salts from undigested food into the
bloodstream. Waste materials are not useful to
body cells, however, and they can even be harmful. So, waste materials will not be
reabsorbed in the large intestine, which also shows us that this option is
incorrect.
This diagram shows us the kidneys,
which are responsible for forming urine. Urine is a waste product that is
formed by the kidneys and is stored in the bladder before it’s removed from the body
during urination. Urination does remove waste
materials and harmful products from the body, just as defecation from the large
intestine does. But the kidneys and bladder are not
technically a part of the digestive system, which is what this question
concerns. Urine is produced by different
organs and is removed from the body via a different tube, the urethra, instead of
via the anus. So, we can conclude that this
option is also incorrect.
The digestive system ends with the
large intestine, where semisolid feces are formed after water and salts have been
absorbed into the bloodstream. And as you might recall, these
feces will be removed from the body by defecation through the anus. Therefore, we can confirm that the
majority of waste materials are removed from the digestive system as (E) feces.
