Video Transcript
In this video, we will learn how to
recall different specialized cells, describe their adaptations, and relate these
adaptations to their functions. So let’s make like a muscle cell
contracting and get started.
First, let’s recall that the cell
is the basic unit of life or the smallest thing that can be considered to be
independently alive. A group of cells that work together
to perform a specific function are called a tissue. A group of tissues that work
together to carry out a function are called an organ. Several different organs that work
together to carry out a specific function are called an organ system. And most multicellular organisms
contain several different organ systems.
When you see a diagram of a cell,
it’s usually generalized or simplified. But the actual cells in our body
are specialized. When we say that a cell is
specialized, we mean that it has specific adaptations that help it to carry out its
job. Or to state things a little more
simply, its form follows its function.
The word “form” refers to the
structure of an object, its shape and its parts, while “function” refers to what a
thing does or what its specific job is. An analogy to specialized cells can
be found in the specialized materials used to build a house. This image is a generalized
house. Like our generalized cell, it’s
simplified and represents many different houses. However, it’s made of parts that
are specialized, different materials that have specific traits that allow them to
carry out a specific job.
The bricks of this house give the
walls their structure and their shape. The transparent windows allow the
occupants to see out and also let light into the house. The wiring carries electricity, and
so on and so forth. Each different part has its own
specific job. In a house, it’s important that
each part match with its function, just like the cells of a living organism. If we built the windows out of
bricks instead of transparent glass, they would no longer function as windows
because their form would be so drastically different.
In the same way, the cells of our
bodies have a form or a shape and structure that’s specific to the job that they
carry out biologically. So when we say that a cell is
specialized, we mean that its form is specific to its function in the same way that
glass is specific to the function of windows. And unlike building materials, when
we’re talking about the form of a cell, we’re referring specifically to its size,
its shape, and its subcellular structures.
So next, we’ll take a look at
several examples of human cells and look closely at how their form supports their
function.
We’ll start with red blood cells,
also called erythrocytes. These cells are quite small in
comparison with other cells of your body, although they’re very numerous. They have a flattened, concave,
disk-like shape, which is due to the fact that mature red blood cells do not possess
a nucleus. These cells also lack mitochondria
as well as most other organelles. They’re basically just sacs filled
with cytoplasm that’s rich in hemoglobin.
Hemoglobin is a large
iron-containing protein which is able to transport oxygen. And transporting oxygen is the
primary function of the red blood cells. These cells are responsible for
carrying oxygen from the lungs to the tissues of the rest of the body, where it’s
used in cellular respiration to generate cellular energy. The size, shape, and subcellular
structures of red blood cells give them special properties, which make them
perfectly adapted to their function of carrying oxygen throughout the blood vessels
of your body.
Let’s continue looking at some more
examples.
Next, we have fat cells, also
called adipocytes. These cells are relatively large in
comparison to the other cells of your body. And they typically have a round,
globular shape. Under a microscope, fat cells look
a lot like soap bubbles. This is because they’re mostly
filled with a huge vacuole, which stores fat. Depending on how much fat needs to
be stored, these already large cells can quadruple in size. Compared to other cells, fat cells
possess very little cytoplasm. Their primary function is to store
excess energy in the form of fat.
Next, we have a type of epithelial
cell called a squamous cell. Compared to the other cells of your
body, they’ve got a small-to-average size. But squamous cells are specifically
characterized by their flat, irregular shape. Because of their flattened shape,
these cells also possess a flattened nucleus. And you can find them stacked in
layers, lining and protecting many of the surfaces inside and outside of your body,
including the outer layer of your skin and the inside of your mouth.
This same type of cell can be found
in a single layer in other parts of your body, where instead of providing
protection, they allow materials to pass through easily. Specifically, in your lungs and in
your capillaries, or the very smallest blood vessels, their flat shape makes it easy
for oxygen and carbon dioxide to move into and out of the bloodstream.
Next, let’s look at another type of
epithelial cell.
Epithelial cells serve the function
of lining certain parts of our body. And ciliated cells are a
specialized type of epithelial cell. These cells are average size and
columnar or oblong in shape. Their characterizing subcellular
structure are the cilia or hair-like extensions of the cell membrane. These cilia are found on one
surface of the cell, and they’re able to move in a wave-like motion. Ciliated cells are found lining the
airways in your lungs and in your nasal passages, where they’re responsible for
moving mucus around. They’re also found in the fallopian
tubes, where they’re responsible for moving the egg cell from the ovary to the
uterus.
Next, we’ll take a look at muscle
cells, specifically skeletal muscle cells. These cells can be up to a few
centimeters long. They’re thin fibers that are
cylindrical in shape. Muscle cells come in three types:
skeletal muscle, smooth muscle, and cardiac muscle. But what they all have in common is
that their primary function is movement. In order to be able to contract and
cause movement, these cells are packed with special proteins. They also have more than the
average number of mitochondria, which provides them with the cellular energy they
need to produce movement. Also, because of their length,
skeletal muscle cells are multinucleated, which means that each cell has more than
one nucleus inside.
Nerve cells are cells that are
specialized for the purpose of transmitting signals from place to place. These cells are responsible for
processing our thoughts, controlling our movement, and helping us to sense the world
around us. They can be very long, up to a
meter in length.
Nerve cells, also called neurons,
have many different subcellular structures, including dendrites which receive
signals from other cells, the axon which transmits the signal, the axon terminal
which delivers the signal, and the myelin sheath, which acts in a similar fashion to
electrical insulation, which serves the function of speeding up the transmission
along the axon.
Remember, these cells can be quite
long. The diagram shows a typical motor
neuron or a neuron that controls movement. But the shapes of nerve cells tend
to vary pretty widely. Depending on their specific
function, they may possess dendrites or not. They may possess axons or not. And they may be myelinated or
not.
The last two specialized cells that
we’ll take a closer look at are our reproductive cells. The male human reproductive cell is
called a sperm, and the female reproductive cell is called an egg cell or an
ovum. Interestingly, the sperm cell is
the smallest cell in the human body, and the egg cell is the largest. This smaller sperm cell is drawn to
give us an idea of the relative size of these cells. And here we have a larger, more
detailed diagram that allows us to see some of the subcellular structures.
The sperm cell consists of a
streamlined head and a long motile or moving tail. Within the head of the sperm, we
find the acrosome, which is a flattened sac that contains enzymes that help the
sperm to penetrate the egg cell. We also find the nucleus, which is
haploid, meaning that it contains half the normal number of chromosomes. At the base of the tail, we find
several mitochondria arranged in a spiral shape. These carry out cellular
respiration that provide the ATP, or cellular energy, that allows the tail to
move. And finally, we have the tail, also
called a flagellum. The movement of the tail propels
the sperm towards the egg cell in a motion not unlike swimming.
The primary function of the sperm
cell is to deliver the father’s genetic material to the egg. When an egg cell and a sperm cell
fuse, it’s called fertilization.
In contrast, the egg cell is large
and round. It also has a protective coating
that serves the purpose of helping to ensure that only one sperm fertilizes the
egg. Like the sperm cell, the egg cell
is haploid, which means that it contains half the normal number of chromosomes. In this way, when the sperm cell
and the egg cell fuse, the cell has the normal number of chromosomes needed for
reproduction.
The cytoplasm of the egg cell also
contains a high concentration of nutrients, which support the development of the
early embryo after fertilization. We also already mentioned the outer
layer which hardens after the egg cell is fertilized. This is meant to ensure that only
one sperm cell penetrates the egg. The purpose of the egg cell is to
facilitate fertilization by allowing one sperm to enter and by providing half of the
genetic material needed to create an offspring. And since the sperm cell is
basically just responsible for delivering DNA, the egg cell is also responsible for
possessing all of the subcellular structures necessary for a fertilized egg cell to
begin to develop into what will eventually become an offspring.
The structure of a cell is always
related to its function. And in this video, we’ve looked at
eight different examples. So let’s wrap up now by taking a
moment to review what we’ve learned. In this video, we learned that the
form or structure of a cell is directly related to its function or its job. We learned about cells specialized
for the transport and storage of materials, two different types of epithelial cells,
cells specialized for movement and communication, and our haploid reproductive
cells.
