Video Transcript
What is the main function of the
digestive system? (A) Synthesizing large molecules
from smaller ones. (B) Collecting and processing
information from external and internal stimuli. (C) Regulating cellular metabolism
and respiration. (D) Breaking down large, insoluble
molecules into smaller, soluble ones. Or (E) maintaining a constant
internal environment.
Whether we choose a healthy green
smoothie or not-so-healthy french fries, the food we ingest takes an amazing journey
through the digestive system, starting at the mouth and ending at the rectum. The main organs of the digestive
system are shown in the diagram and include the esophagus, stomach, and small and
large intestines, as well as critical accessory organs, such as the liver and
pancreas.
Digestion is a process in which
large molecules, or macromolecules, are broken down into smaller molecules. It is essential because unless the
large, insoluble nutrients in food are broken into smaller forms, they will not be
absorbed into the bloodstream. And we will not be able to use them
for cellular respiration, growth, or repair.
The biological macromolecules in
food are broken down into their smaller subunits, or monomers, by enzymes that are
specific to the type of substrate they break down. For example, proteins are broken
into amino acids by a group of enzymes called proteases. Once they are fully broken down,
the monomers move out of the digestive system into surrounding capillaries. The blood then carries these
smaller nutrients to the body cells, where they can be reassembled into an
incredibly diverse range of molecules to be used by the body.
Returning to our answer options, we
can see that the correct answer is (D). The main function of the digestive
system is breaking down large, insoluble molecules into smaller, soluble ones.