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Plant and Animal Cell Organelles
Organisms and Environments
A Framework for Function
Lexile 930L
1  What makes up a cell? Did you know that there
are billions of cells moving around in your body
at this very moment? Without cells, our bodies
would not be able to function. When was the
cell discovered? In 1665, a scientist named
Robert Hooke looked through his microscope
to study a piece of cork. When he gazed upon
the cork, he saw rows and rows of small
rectangular holes. Robert Hooke had just
discovered cells. This exciting discovery led to
the invention of a better microscope by Anton
Van Leeuwenhoek in 1673. His microscope was
specifically designed to view the interesting
“animalcules” described by Hooke. With this improved microscope, Van Leeuwenhoek saw
single-celled protozoa in pond scum and discovered blood cells! It is because of scientists like
Van Leeuwenhoek and Hooke that we know so much about cells today.
2  A cell is the smallest unit that is truly alive. Our basic knowledge of cells is summarized in the
cell theory that was proposed by scientists nearly 150 years ago. Cell theory is composed of
three major points: all living things are composed of cells, all cells come from pre-existing cells,
and cells are the smallest units of life.
3  There are two different types of cells known—prokaryotes and eukaryotes. Prokaryotes are
simpler and smaller. They only have a membrane and a cell wall that enclose the rest of their
insides. Eukaryotic cells are much more complex and have a nucleus. Your body is composed
of eukaryotic cells. Eukaryotes are up to ten times larger than the average prokaryote cell.
Another important characteristic of the eukaryotic cell are the membrane-enclosed sub-cellular
organelles that will be further explained later in this passage.
4  All cells are surrounded by a cell membrane. A cell membrane is a boundary that separates
the cell from the outside environment. Basically, it is like a fence. Like the skin on your body,
this membrane acts as a protective layer that covers the cell's surface. It allows some things to
be excreted out of the cell, such as wastes, and allows some things in, like nutrients and
oxygen.
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Plant and Animal Cell Organelles
Organisms and Environments
5  Plant cells also have a cell wall, which is not found in animal cells. Cell walls are also found in
the cells of fungi and bacteria. The cell walls give support to the plant cell and provide a basic
framework. It is a second layer around the cell membrane for double protection. The cell wall
is different from the cell membrane in that it is rigid and strong. The cell wall is very important
because it provides support for plant cells to grow tall.
6  Cytoplasm is a gel-like material that fills all cells. This clear, thick, jelly-like material holds all of
the cell's material together on the inside. In eukaryotic cells, it is found between the cell
membrane and the nucleus. Organelles move about freely in the cytoplasm, and other cell
activity occurs here. In prokaryotic cells, all cellular activities occur in the cytoplasm. This gellike material is held in by the cell membrane and is constantly moving.
7  Eukaryotic cells contain organelles, but prokaryotes do not. Organelles are structures inside a
eukaryotic cell that perform the functions necessary for the cell to survive. There are several
different types of organelles within a cell that allow it to survive. Let's get an even closer look at
some of these vital cellular components.
8  If the cell was a ship, then the nucleus would be the captain. The nucleus is an organelle inside
the cell that guides all activity. It is the most important part of the eukaryotic cell because the
nucleus contains DNA, which provides specific instructions for the cell's actions. DNA tells the
cell how to produce new cells and perform all the cell's jobs. It also contains hereditary
material, which will pass on specific information to future cells. Without DNA, the cell would not
know how to operate. The nucleus is in all eukaryotes, while in prokaryotic cells, the DNA floats
freely in the cell's cytoplasm. The nucleolus is a special structure within the nucleus, and its
function is to make ribosomes. Ribosomes produce proteins. The nucleus is protected by the
nuclear membrane. It is like an additional guard that controls the movement of materials in and
out of this special area.
9  The motors that fuel the entire cell's production are known as the mitochondria. These are a
cell's “power plants.” Located in plant and animal cells, mitochondria produce ATP, the energy
source for everything a cell needs to do. ATP is like gas for a car, and the mitochondria are
responsible for producing it. They do this by breaking down sugars using oxygen. The
breakdown process is known as cellular respiration.
10  Although plants use mitochondria to make ATP as an energy source, these cells also produce
their own sugar through unique organelles called chloroplasts. Chloroplasts are organelles that
produce chlorophyll, which traps the Sun's energy. The chlorophyll transforms this energy into
sugar to be used in its mitochondria. This process is called photosynthesis, and the end waste
product is oxygen. Without plant cells and the process of photosynthesis, humans and other
organisms would not have oxygen to breathe.
11  These are just some of the remarkable organelles found in the cells of eukaryotes. Remember
that the cell wall and chloroplasts are found in plant cells, but not animal cells. Who would have
guessed there would be so much to see when we take a closer look inside of cells?
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Plant and Animal Cell Organelles
Organisms and Environments
For questions 1 and 2, use this diagram of the cell where one of the mitochondria has
been enlarged.
1
From the information in the passage and the diagram, what can you
conclude about the structure of mitochondria?
A
They are membrane-bound organelles with a second, folded
membrane inside to provide extra area for cellular respiration.
B
They take instructions from DNA and make proteins.
C
They break down sugars to provide energy for the cell.
D
They are organelles, which are a group of flattened membrane sacs
stacked on top of each other.
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Plant and Animal Cell Organelles
Organisms and Environments
2
3
From the information in the passage and the diagram, what can you
conclude about the function of mitochondria?
A
They are membrane-bound organelles with a second, folded
membrane inside to provide extra area for cellular respiration.
B
They take instructions from DNA and make proteins.
C
They break down sugars to provide energy for the cell.
D
They are organelles, which are a group of flattened membrane sacs
stacked on top of each other.
Which of the following statements best captures the main point of
paragraph 3?
A
A cell is the smallest unit that is truly alive.
B
All cells are surrounded by a cell membrane.
C
Cytoplasm is gel-like material that fills all cells.
D
Plant cells have cell walls.
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Plant and Animal Cell Organelles
Organisms and Environments
4
In the passage, an analogy was given describing the function of a cell in
simple terms by comparing it to a ship. Complete this analogy about the
function of cell parts.
A cell is to a board game as —
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A
DNA is to the rule book.
B
a nucleus is to the rule book.
C
endoplasmic reticulum is to the rule book.
D
a ribosome is to the rule book.
What does the word sub-cellular in paragraph 3 mean?
A
more complex than a cell
B
taken away from a cell
C
hidden underneath a cell
D
located within a cell
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