Video Transcript
In this video, we will explore the
levels of biological organization from cell to organism. We’ll investigate some
examples. Then we’ll answer some practice
questions together. And finally, we’ll summarize what
we’ve learned. So, let’s get started.
One of the core concepts of biology
is this idea of hierarchical organization. The word hierarchical means based
on rank. And in biology, we tend to rank
things based on size and complexity. For example, you may already know
that a cell is made of several organelles. The functional parts of those
organelles are composed of macromolecules. Macromolecules are made from more
simple molecules. And molecules are composed of
atoms. Even atoms consist of smaller parts
that you might’ve learned about in chemistry. For the purposes of this lesson,
we’ll be focusing on the levels of organization from cell to organism.
Let’s begin with the smallest or
least complex of these, the cell. You may already know the cell as
the basic unit of life. This means that a cell is the
smallest thing that can be considered independently alive. The human body contains trillions
of individual cells that could be categorized into about 200 different types. Different cells have different
shapes and different parts because they have different jobs or perform different
functions. Skin cells and other cells whose
job it is to line the surfaces of our bodies tend to be thin and flat, while fat
cells will be big and round with lots of space for storage. Muscle cells are long and full of
special proteins that allow them to shorten or contract.
Nerve cells are also very long, and
they’re specialized to transmit signals rapidly from place to place within the
body. Mature red blood cells are so
simple they don’t even have a nucleus. They have one job which is to
transport oxygen from the lungs to the tissues of the body that need it. Each cell has a special shape or
form that allows it to do its job or function. But our bodies are made of
trillions of cells. How do they organize themselves to
do all of the jobs it takes to keep us alive? Let’s return to our definition of a
cell as the basic unit of life.
A unit is not only a thing that can
be considered to be complete on its own, but also a building block that can come
together to form a larger whole. Cells are the units that make up
tissues. Tissues are the units that make up
organs. Organs are the units that make up
organ systems. And organ systems can be considered
the units that come together to make up one multicellular organism. So next, let’s take a closer look
at tissues. What exactly is a tissue? A tissue is a group of cells that
work together to perform a specific function. There are four types of tissue in
the human body: nervous tissue, connective tissue, muscle tissue, and epithelial
tissue.
Within the body, nervous tissue
handles information processing, communication between body parts, and control of
bodily functions. The function of connective tissue
is to support, anchor, and connect the different parts of the body. Muscle tissue is responsible for
all movement, while epithelial tissue functions as the lining for most parts of the
body. Epithelial tissue is also
responsible for secretion and absorption. Let’s look at an example. Let’s recall our definition. A tissue is a group of cells that
work together to perform a specific function. A tissue you may already be
familiar with is blood. Blood is a type of connective
tissue.
Blood is made up of red blood cells
that carry oxygen, white blood cells that protect the body from infection, and
platelets that help your body to form clots to prevent bleeding. All of these are suspended in a
liquid known as blood plasma. The main function of blood is
transportation. It moves things around the body
like oxygen, nutrients, waste, hormones, and more. Blood also serves the purpose of
protecting the body from invasion and infection. It also has some regulatory
functions such as helping to maintain body temperature and fluid levels.
If you think of the different cells
in the body as an alphabet, the tissues are like words. The different types of cells within
a tissue work together to perform a specific function the same way that different
letters come together to give each word a specific meaning. Next, let’s take a closer look at
organs.
An organ is a group of tissues that
work together to perform a specific function. Your body contains many, many
different organs such as your tongue, both of your eyes, each of your individual
teeth, every separate hair on your body, the bones that make up your skeleton, each
of your various glands, and so many more. Out of all of the organs in your
body, five of them are considered vital or organs that you simply could not live
without. These five organs are your brain,
your liver, your kidneys, your heart, and your lungs. Let’s look at an example and more
closely examine the heart.
Let’s recall our definition that an
organ is a group of tissues that work together to perform a specific function. Your heart is one of your five
vital organs. Your heart contains all four types
of tissues. It’s primarily made of a special
type of muscle tissue called cardiac muscle. Cardiac muscle is only found in the
heart. It possesses nervous tissue which
helps to control the speed of your heartbeat. There are several types of
connective tissue found in your heart, the most obvious of which is blood. And your entire heart is lined
inside and out with epithelial tissue. All of these tissues work together
to perform the heart’s primary function, which is to pump blood to and from the
lungs and the tissues of the body.
Returning to our analogy, if cells
are like an alphabet and tissues are like words, then organs are like sentences. Tissues work together so that an
organ can perform a specific function the same way that words work together to give
each sentence one specific meaning. Next, let’s take a look at organ
systems. Well, you may have already guessed
that an organ system is a group of organs that work together to perform a specific
function. The human body has about 11 organ
systems. And they work together in closely
integrated ways to carry out your life functions, functions like protection, support
and movement, control and integration, transport of materials, and reproduction. Let’s take a closer look at your
circulatory system.
Let’s recall our definition. An organ system is a group of
organs that work together to perform a specific function. This is a highly simplified diagram
of your circulatory system. The circulatory system contains one
of our vital organs, the heart, which we discussed in more detail a little bit
earlier. The circulatory system also
contains veins, which carry blood towards the heart, as well as arteries, which
carry blood away from the heart, and also the capillaries, which are tiny blood
vessels. These are the sites of gas and
nutrient exchange between the blood and the tissues of the body.
The circulatory system has many
functions. Its primary function is to
transport materials throughout the body, materials like gases, hormones, nutrients,
and wastes. The circulatory system also helps
to fight off infection and to maintain body temperature. Returning to our analogy, if the
cells of our body are like letters in an alphabet and the tissues are like words
formed from those letters and the organs are like sentences built from those words,
then our organ systems are like paragraphs. Organs work together within an
organ system to perform a specific function the way that written sentences come
together into a complete paragraph to convey one idea.
Finally, let’s take a look at this
term, “organism.” An organism is what we call one
living thing. Some organisms are made of just one
cell, organisms like bacteria, yeast, and most species of protists. In these organisms, just one cell
carries out all the functions necessary for life. We refer to these organisms as
unicellular, uni- meaning one. Organisms like you, me, and other
animals, all plants, and most species of fungi have many cells which are arranged
into issues which are arranged into organs which are arranged into organ
systems. These are known as multicellular
organisms, multi- meaning many.
Returning one last time to our
alphabet analogy, if cells are like letters and tissues are like words, organs are
like sentences and organ systems are like paragraphs, then a multicellular organism
is like an entire story. Organ systems come together to
carry out all the essential functions of life within an organism the way that
paragraphs come together to convey the meaning within a story. Now that we’re familiar with the
levels of organization and we’ve looked at examples of cells, tissues, organs, organ
systems, and organisms, we’re ready to try some practice questions.
Put the following structures in the
order in which they are organized in the human body from smallest to largest:
tissues, cells, organ systems, organs.
This question is asking us to place
these four key terms, tissues, cells, organ systems, and organs, in order from
smallest to largest. The four terms in question
represent four of the levels of biological organization. We’re being asked to rank them from
smallest to largest or from least complex to most complex. In order to rank these terms, we’ll
use this chart and this definition. A blank is a group of blank that
work together to perform a specific function.
The only term that doesn’t fit this
definition is the cell, which we know is the basic unit of life. And since that means it’s the
smallest thing that can be considered to be independently alive, we know that the
term cell goes in the smallest spot on our chart. Now, we have three more terms to
place. Next, let’s try to place the term
tissues. A tissue is a group of cells that
work together to perform a specific function. So, we know where to place tissue
in our levels of biological organization chart, directly above cells.
Next, let’s try organ systems. An organ system is a group of
organs that work together to perform a specific function. Since we didn’t say it’s a group of
tissues, we’ll go ahead and skip a space and put it at the top of our levels of
biological organization chart. Let’s go ahead and define our last
term organs. An organ is a group of tissues that
work together to perform a specific function. Since we know that tissues make
organs and organs make organ systems, we know exactly where to place the term organ
in our levels of biological organization chart.
Using the definition of each term
and this handy organizational chart, we’re ready to answer our question. The order of these structures from
smallest to largest is cells, tissues, organs, organ systems.
Let’s try another question.
What organ system are the organs in
the picture key components of?
The question is telling us that
this diagram is of organs. And it’s asking us which organ
system these organs belong to. So our first step is to identify
the organs in the picture. The organs pictured are the
lungs. The human body has about 11 organ
systems, and we need to figure out which of these 11 your lungs belong to. Well, we know that our lungs allow
us to breathe in oxygen and to breathe out carbon dioxide. This process is commonly known as
breathing or, more technically, as respiration. And here’s our most important
clue. Since our lungs play a key role in
respiration, we can conclude that they’re key components of the respiratory organ
system.
So, returning to our question,
“What organ system are the organs in the picture key components of?”, the lungs in
the picture are key components of the respiratory system.
Let’s take a moment and review what
we’ve learned in this lesson. In this video, we’ve learned that
cells make up tissues, tissues make up organs, and organs make up organ systems. We can call this hierarchical
ranking from smallest to largest or from most simple to most complex the levels of
biological organization. We also learned that there are four
types of tissues in the human body. We reviewed the five vital
organs. And we learned that there are about
11 different organ systems that carry out our life processes.
