Video Transcript
In this video, we will learn about
the subcellular structures called organelles found in plant and animal cells. We will describe their form and
their functions. Then we’ll look at some practice
questions. And finally, we’ll review what
we’ve learned. Let’s begin by describing cells in
general. Hopefully, some of this is
information that you’re already familiar with.
Cells are the basic unit of
life. That means that cells are the
smallest thing that can be considered to be independently alive. All living things are made of one
or more cells: plants, animals, fungi, protists and bacteria, everything that’s
considered to be alive. There are certain things that all
cells have in common. All cells have a way to define
their boundaries and to control what enters and leaves the cell. This is called the cell
membrane. All cells have a liquid substance
that fills their internal space. This jellylike fluid is called
cytoplasm.
All cells contain genetic material
that directs the functions and activities of the cell. This genetic material is called
DNA. If the DNA of the cell is floating
in the cytoplasm, the cell is classified as prokaryotic. Bacteria are prokaryotic cells. If the DNA is contained and
protected within a structure known as the nucleus, the cell is classified as
eukaryotic. Plants, animals, fungi, and
protists are all made of eukaryotic cells. Lastly, all cells contain tiny
structures that interpret the information stored in DNA by translating it into
proteins. These structures are called
ribosomes.
These four structures, the cell
membrane, the cytoplasm, DNA, and ribosomes, are found in all living cells. However, different types of cells
have different structures within them in addition to these four. Next, let’s take a look at the
structures within an animal cell. Animals like you, me, cats, fish,
lizards, insects, birds, and more are made of cells that have certain features in
common. This is a simplified drawing of an
animal cell. This is the cell membrane, which we
introduced a little bit earlier. The cell membrane defines the
boundary of the cell and controls what can enter and what can leave.
The cell membrane is made of
molecules called phospholipids. These phospholipids are arranged in
two layers, so we refer to the cell membrane as a phospholipid bilayer, bi- meaning
two. The phospholipids arranged in this
way give the cell membrane lots of special properties, like being flexible and
self-sealing and being permeable to some things but not to others. We’re also familiar with the
cytoplasm that fills the inside of the cell. Cytoplasm is a word that means cell
liquid. Cytoplasm is mostly water, but it
also contains proteins, nutrients, and minerals.
We often draw cells as
two-dimensional, but it’s important to remember that they are not flat. You can think of the cell as a
water-filled balloon. The outer membrane is thin and
flexible. The inner filling helps to give the
cell its three-dimensional shape. The subcellular structures or parts
that make up a cell are called organelles. Organelle is a term that means
little organs. One example of an organelle is the
nucleus, which we’ve learned stores and protects the genetic material or DNA inside
of all eukaryotic cells. Each cell only contains one
nucleus. Some students draw an analogy
between the nucleus in your cell and the brain in your body because the nucleus
stores information and controls the activities of the cell.
The nucleus can also be
distinguished by some other special features. The membrane that surrounds the
nucleus is like the membrane that surrounds the cell, but the nucleus has a double
membrane. The nucleus also has pores. The pores allow certain things to
easily move into and out of the nucleus but keeps the DNA safely protected
inside. The ribosomes are tiny organelles
that interpret the genetic code and make proteins. Proteins are important biological
molecules that carry out the majority of a cell’s functions. The way this happens is called the
central dogma of biology, or protein synthesis, which, put simply, states that DNA
is transcribed into RNA, which is then translated into a protein.
In this drawing, we see one other
important organelle. These bean-shaped structures are
called mitochondria, the singular of which is mitochondrion. Mitochondria are often referred to
as the powerhouse of the cell because they convert the chemical energy found in
glucose, which animals get from their food, into stored cellular energy in a
molecule called ATP. The process of turning glucose and
oxygen into the stored energy in ATP, water, and carbon dioxide is called cellular
respiration. This process is the reason that we
breathe in oxygen and breathe out carbon dioxide, a cycle also known as
respiration.
Mitochondria are bean shaped. They possess a smooth outer and a
folded inner membrane. The folds in the inner membrane
facilitate the complex chemical reactions involved in cellular respiration. Mitochondria, interestingly,
contain their own ribosomes and DNA, a feature which lead scientists to believe
that, long ago, these were separate prokaryotic organisms that formed a symbiotic
relationship with eukaryotic cells. Most animal cells also contain a
number of additional organelles. For now, let’s move on and take a
look at the structures within a plant cell.
Here we see a simplified diagram of
a plant cell. It’s different than an animal cell
in several different ways. Sometimes students mistakenly get
the idea that all plant cells are square and all animal cells are round. The truth is that plant cells and
animal cells come in a variety of different shapes depending on their function. The correct way to distinguish
between them is to look at the structures inside. Plant cells contain all of the
structures that we’ve already labeled in animal cells. So we won’t read them again right
now. Instead, we’ll just focus on the
three structures that you find in plant cells and not an animal cells.
You’ll notice that this plant cell
has a thick outer layer that the animal cell did not. The cell wall is a tough outer
structure that gives the plant cell its shape. Under different conditions, the
cell may fill with water and become turgid. Or fluid may leave the cell, making
it flaccid. In all conditions, the cell wall
remains unchanged. Plant cells contain a special
organelle that they used to store water. The central vacuole looks like a
big bubble and, in some cases, will take up the majority of the space in the plant
cell. Other types of cells, including
animal cells, also contain vacuoles. But the central vacuole is found
only in plant cells. It’s especially large and helps to
give the plant cell its structure.
The last organelle that we see here
that’s present in plant cells and not in animal cells is the chloroplast. Chloroplasts are the part of the
plant cell that give plants their green color. Since plants don’t eat food like
animals do, they have to synthesize or make their own glucose using sunlight. This is a process known as
photosynthesis, a word that means to make something using light. During photosynthesis, plants use
water, the energy in sunlight, and carbon dioxide to make glucose and oxygen. Let’s take a closer look at a
chloroplast.
The chloroplast is surrounded by a
double membrane. It’s filled with series of stacked
membranes that facilitate the complex chemical reactions involved in
photosynthesis. Like the mitochondria, a
chloroplast has its own DNA and ribosomes, leading scientists to believe that they,
too, were once independent prokaryotic organisms that formed symbiotic relationships
with eukaryotic cells. Now that we’ve learned about the
subcellular structures found in plant cells and in animal cells, let’s try a few
review questions.
The diagram provided shows the
basic outline of an animal cell. Which component is represented by
W? Which organelle is represented by
Z?
Before we attempt to answer the
question, we’ll go ahead and review the things that we know about animal cells. An animal cell is a type of
eukaryotic cell. This means that this cell possesses
a nucleus in which the DNA is stored. Also, since we know that this is an
animal cell and not a plant cell, we know that this cell will not have a cell wall,
will not possess a central vacuole, and will not contain any chloroplast to carry
out photosynthesis. So what is in the animal cell that
we see pictured here?
Well, first, this cell, like all
living cells, possesses a cell membrane. The cell membrane defines the
boundary of the cell and also controls what enters and leaves. The animal cell possesses
cytoplasm, the jellylike substance that fills the cell and helps to give it its
shape. In this cell, we also see several
mitochondria. These organelles are responsible
for carrying out cellular respiration, a process which stores cellular energy in the
form of ATP. Mitochondria are bean shaped and
possess a smooth outer and folded inner membrane.
Finally, we see the nucleus, which
we mentioned just a little bit earlier. The nucleus is surrounded by a
double membrane that has openings called nuclear pores. The nucleus is responsible for
storing and protecting the genetic material, also called DNA. Now, we’re ready to answer our
question. Which component is represented by
W? W represents cytoplasm. Which organelle is represented by
Z? Z represents the cell membrane.
Let’s try another practice
question.
Which of the following organelles
is found in the majority of both plant and animal cells? (A) Chloroplast, (B) cell wall, (C)
large vacuole, or (D) cell membrane.
This question is asking us to
select the organelle among the choices which we’re likely to find in both plant and
animal cells. First, let’s recall that both plant
and animal cells are types of eukaryotic cells, meaning that they have many things
in common, most importantly, a nucleus that contains and protects the DNA. While these cells have much in
common, they also have many differences. Let’s review what we know.
Here we have a simplified diagram
of an animal cell and a plant cell. We can see that both the plant and
animal cell possess a cell membrane, a thin and flexible outer layer that defines
the cells boundaries and controls what enters and what leaves. Both the plant and animal cell
possess mitochondria, bean-shaped organelles with double membranes that are the site
of cellular respiration. Both the plant and animal cell
possess ribosomes, tiny organelles that are the site of protein synthesis.
And finally, as we’ve mentioned
before, both of these cells will possess a nucleus, an organelle found in all
eukaryotic cells whose job it is to protect and store the genetic material or
DNA. However, we see some additional
structures in the plant cell that we did not see in the animal cell. The plant cell possesses a cell
wall or a rigid outer layer. The plant cell also possesses a
central vacuole that functions to provide cell storage as well as cell
structure. The plant cell also contains
chloroplasts, which are the site of photosynthesis.
Now, we’re ready to answer our
question. Which organelle is found in both
plant and animal cells? Well, chloroplasts are found in
only plant cells, and so are cell walls. A large vacuole, also called a
central vacuole, is another structure found in plant cells and not in animal
cells. However, the cell membrane, which
defines the boundary of the cell and controls what can enter and what can leave, is
found in both plants and animal cells.
Let’s try one last practice
question together.
State the organelle being
described: Only found in plant cells, this is a layer made of cellulose that
surrounds the cell to provide structure and support.
This question is asking us to
identify the organelle or subcellular structure being described in the prompt. It must be exclusive to plant
cells, found on the outside of the cell, and it must provide structure and support
to the cell. In order to answer this question,
first we’ll draw and label a plant cell. Then we’ll identify the parts that
are only found in plant cells. And then we’ll be able to choose
our answer.
Here’s a simplified diagram of a
plant cell. Let’s label what we see. The plant cell has a cell membrane,
which defines the boundary of the cell and controls what enters and what leaves. The plant cell contains cytoplasm,
a jellylike fluid that fills the internal space of the cell. The plant cell contains ribosomes,
tiny organelles that are the site of protein synthesis. We also see several mitochondria,
bean-shaped organelles that are the site of cellular respiration. The plant cell also contains a
nucleus, an organelle which stores and protects the genetic material or DNA.
In addition to the structures we
listed, the plant cell possesses a cell wall, a rigid outer layer that provides
structure and support. It possesses several chloroplasts,
organelles that give the plant its green color and are the site of
photosynthesis. The plant cell also possesses a
large central vacuole, an organelle that provides both storage and structure to the
plant cell. Well, we’ve labeled all the parts
of our cell.
Let’s recall that our question is
looking for an organelle that’s only found in plant cells. All of these organelles to the
right are found in both plants and animal cells, while the ones on the left are only
found in plant cells. So the correct response must be
cell wall, chloroplast, or central vacuole. Of these three, the layer that
surrounds the cell to provide structure and support is the cell wall.
Next, let’s take a moment to review
what we’ve learned in this lesson. In this video, we learned that
organelle is what we call specialized subcellular structures. We learned there are certain
organelles that can be found in all living cells, some organelles that are found in
both plant and animal cells, and some organelles that are found in plant cells but
not animal cells. All cells possess a cell membrane,
cytoplasm, and ribosomes. Also found in both plant cells and
animal cells, are several mitochondria and a nucleus. And finally, organelles that we
find in plant cells and not in animal cells include the cell wall, the central
vacuole, and the chloroplasts.