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7.12D: Plant and Animal Cell Organelles
Organisms and Environments
A Framework for Function
(Lexile 740L)
1  What makes up a cell? Did you know that there
are billions of cells in your body right now?
Without cells, our bodies would not be able to
function. When was the cell discovered? In
1665, a scientist named Robert Hooke looked at
a piece of cork through a microscope. He saw
rows and rows of small rectangular holes. Robert
Hooke had just discovered cells. This discovery
led to the invention of a better microscope by
Anton Van Leeuwenhoek in 1673. His microscope was designed to view the interesting
things described by Hooke. With this improved microscope, Van Leeuwenhoek discovered
blood cells and single-celled organisms. 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 the following three major points. All livings things are composed of cells. All
cells come from pre-existing cells. 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 have a much more complex and have a nucleus. Your body
is made of eukaryotic cells. Eukaryotic cells can be up to ten times larger than the
prokaryote cell. Another characteristic of the eukaryotic cell are the membrane-enclosed
sub-cellular organelles. These 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. It is like a fence. This membrane acts like the skin on
your body. It is a protective layer that forms the cell’s surface. It allows some things to
come out of the cell, such as wastes. It allows other things in, like nutrients and oxygen.
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7.12D: Plant and Animal Cell Organelles
Organisms and Environments
5 Plant cells also have a cell wall. It is also found in cells of fungi and bacteria. This is never
found in animal cells. 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 walls
give support to the plant cell. They also provide a basic framework for the whole plant. The
cell wall is very important. Its support allows the plant to grow tall.
6 Cytoplasm is gel-like material that fills all cells. This clear, jelly-like material holds all of the
cell’s contents. The cytoplasm is held in by the cell membrane. In eukaryotic cells, it is
found between the cell membrane and the nucleus. Organelles move about in the
cytoplasm, and other cell activity occurs here. In prokaryotic cells, all cellular activities occur
in the cytoplasm.
7 Eukaryotic cells contain organelles, but prokaryotes do not. Organelles are structures inside
an eukaryotic cell. They perform the functions necessary for the cell to survive. There are
several different organelles within a cell that allow it to survive. Let’s get an even closer
look at some of these important 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. The
nucleus contains DNA, which provides the 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 information to future cells. Without DNA, the cell would not know
how to operate. The nucleus is in all eukaryotes. In prokaryotic cells, the DNA floats freely
in the cell’s cytoplasm. The nucleolus is a special structure within the nucleus. Its function
is to make ribosomes. Ribosomes make proteins. The nuclear membrane protects the
nucleus from harm. 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.” Mitochondria make ATP, the energy source for everything a cell
needs to do. ATP is like gas for a car. The mitochondria must make enough for the cell.
They do this by breaking down sugars using oxygen. The breakdown process is known as
cellular respiration. Mitochondria are found in both plant and animal cells.
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7.12D: Plant and Animal Cell Organelles
Organisms and Environments
10 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. This chemical traps the Sun’s energy. The chlorophyll then
transforms this energy into sugar to be used in its mitochondria. This process is called
photosynthesis. 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 important 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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7.12D: Plant and Animal Cell Organelles
Organisms and Environments
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2
3
The passage describes a cell as —
A
the smallest unit of life that can perform all life processes.
B
a prokaryote.
C
a cell wall.
D
molecules surrounded by membranes and cell walls.
What are organelles?
A
Prokaryotes
B
Eukaryotes
C
Structures inside a cell that perform the functions necessary for the
cell to survive
D
The smallest unit of life that perform all life processes
What is the “motor” that fuels the entire cell’s production is known as?
A
Golgi bodies
B
Mitochondria
C
Ribosome
D
Nucleus
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7.12D: Plant and Animal Cell Organelles
Organisms and Environments
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In the passage, an example of a cell was given in simple terms to
describe its function: A cell is to a ship as —
A
a nucleus is to a captain.
B
DNA is to a captain.
C
endoplasmic reticulum is to a captain.
D
a ribosome is to a captain.
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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