Video Transcript
What is the key difference between
a stem cell and a normal body cell? (A) Stem cells are specialized to
carry out a particular function, whereas normal body cells are unspecialized. (B) Normal body cells contain
genetic material, whereas stem cells do not. (C) Stem cells are only found in
embryos, whereas normal body cells are only found in adults. (D) Stem cells can divide and
replicate, whereas normal body cells cannot. (E) Normal body cells are
specialized to carry out a particular function, whereas stem cells are
unspecialized.
This question asks us about the key
difference between a stem cell and a normal body cell. So what is a stem cell?
Stem cells are unspecialized cells
that have the capacity to differentiate into different types of specialized
cells. Our bodies are composed of many
different specialized cells. These different cells perform many
different functions. Each cell type has specific
features that make it good at its job. For example, red blood cells are
specialized cells. They are adapted to carry oxygen
around the body and have a variety of features that enable them to do this. They contain hemoglobin, which
oxygen binds to. They are shaped like a biconcave
disc, which gives them a large surface area across which oxygen can diffuse. And they are small and flexible so
can squeeze through narrow capillaries.
A red blood cell is very different
to, for example, a liver cell or skin cell. These cells all have different
roles in the body and therefore require different features. All of our cells originated from a
ball of undifferentiated stem cells.
The early embryo is made up of stem
cells. These have the potential to
differentiate into any type of specialized cell in the body. The embryo develops into a fetus
and eventually a fully fledged baby, with all the specialized cells required to form
all the tissues, organs, and organ systems of a human.
Now we have learned about stem
cells, let’s discuss our answer options.
First, we can eliminate answer
(A). We know that stem cells are not
specialized. They differentiate during
development to form specialized body cells.
We can also eliminate answer
(B). Both body cells and stem cells have
genetic material. Stem cells must contain genetic
material because this acts as a set of instructions for differentiation.
Now let’s look at answer choice
(D). We know that stem cells must
replicate. Early-stage human embryos start out
as just a small number of stem cells, which must replicate and differentiate to form
complex adults. However, normal body cells must
also replicate, although perhaps less readily. Replication of body cells is used
in the immune system, after injury, and to replicate old or dead cells in the blood
and organs. So we can eliminate answer (D) as
well.
We have already discussed how stem
cells are found in embryos. In addition, even as adults, we
maintain a small number of stem cells in many of our tissues, for example, in the
brain, bone marrow, and skin. So answer (C) is incorrect.
We are left with our correct answer
choice. The key difference between a stem
cell and a normal body cell is given in answer choice (E). Normal body cells are specialized
to carry out a particular function, whereas stem cells are unspecialized.
