Video Transcript
The figure shows changes that occur
in the body during fasting. What process ,Y , is stimulated in
the liver when glucagon levels in the blood increase? (A) Glycogen is broken down. (B) Glycogen is made. (C) Glucose is used for
respiration. (D) Glucagon is taken up. Or (E) glucagon is broken down.
All these terms in the different
answer choices, glycogen, glucose, and glucagon, sound very similar, which can be
fairly confusing. Let’s clarify them step by
step.
This question presents us with a
figure that shows the changes occurring in some organs of the body during fasting,
which refers to a time when an individual is not consuming food. This means that they will not be
obtaining any sugars, like glucose, which is an essential nutrient required for
cellular respiration, the process that our body cells use to release energy.
Glycogen is a large carbohydrate
that is made up of long, branching chains of glucose molecules. It is how animals like humans store
glucose in their cells, particularly in the liver.
In order to answer this question,
let’s consider some key responses of the pancreas and liver during times of
fasting. When blood glucose levels are low,
as in times of fasting, the pancreas is alerted. And it will begin to secrete a
hormone called glucagon. Glucagon has several effects within
the body, such as stimulating glycogenolysis in the liver.
You may recall that the suffix
-lysis often refers to breaking down substances. So glycogenolysis is the breakdown
of glycogen molecules. As we learned, glycogen is made up
of lots of subunits of glucose. So this process creates new glucose
molecules, which are then released into the blood, therefore helping to increase
blood sugar levels back to a healthy range. Allowing cells to have an adequate
supply of glucose means that they can continue to function properly.
We now know that glycogen is stored
in the liver. And high levels of glucagon in the
blood will stimulate the breakdown of glycogen, thereby increasing blood glucose
levels. We can use this information to
answer the question correctly. The process stimulated in the liver
when glucagon levels in the blood increase, and the correct answer to our question,
is (A); glycogen is broken down.
