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Unicellular Organisms 6th Grade Science
By Nathan Boyd
Name
Period
You know that living things are made of cells. Some living things
are made of only one cell. They are called unicellular. Uni- means one,
as a unicycle has only one wheel. Most of us don't think about these
unicellular creatures very much, but they are all around us. Most are
invisible without a microscope, but a few can be seen with the naked
eye.
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The main groups of unicellular organisms are bacteria, protozoa, unicellular algae, and
unicellular fungi or yeasts. Each species is unique. They can be interesting to study because of
their intricate and beautiful patterns. Some are sensitive to light. They may move toward it or
away from it. They have novel ways of moving around. They also respond to touch. Some can
live in very extreme environments.
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Single-celled organisms have been on Earth for 3.8 billion years. They have had a long time
in which to adapt. Scientists believe they were the first forms of life on Earth. Although they are
only one cell, they are complex. The more that we learn about them, the more marvelous we
find them to be.
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Their shapes may be spheres, oblong, or spiral. A spherical shape helps keep them from
drying out. That would be fatal to a cell. An oblong shape increases the cell's surface area for
chemical processes. A spiral shape makes it easier for the organism to move.
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Unicellular organisms have unusual ways of moving. The euglena have tiny hair-like
structures called flagella. The flagella beat in the water and move the cell forward. The word
flagellum means whip in Latin. Flagella (pronounced fla-jell-ah) is the plural form. Some have
groups or rows of structures that move together like oars. These are called cilia (pronounced
silly-ah). Cells with cilia move fast! One unicellular organism that moves with cilia is the
paramecium.
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Some unicellular organisms are able to change their shapes. Amoebas are "shape-shifters"
that can extend parts of themselves into what are called pseudopodia and then flow in the
direction in which they wish to go. Pseudopodia (pronounced sue-do-pode-ee-ah) means false
feet. If they find something to eat, they can engulf, or surround, the particle with their
pseudopodia. Then they pull themselves around it to digest it.
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Just as the amoeba uses its pseudopodia for both movement and feeding, some unicellular
organisms with cilia also use the cilia to catch food. The stentor has cilia that beat rhythmically,
which draws food into its mouth. This adaptation allows stentors to spend most of their lives
attached to a surface. They can then save their energy for catching food.
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Some unicellular organisms live in extreme environments. They are called extremophiles.
They have been found in such extreme habitats as Antarctic ice and in very hot deep-sea vents.
The ability of organisms to adapt to extremely hot or cold environments gives scientists hope
that signs of life will eventually be found on other planets. They believe that Mars and Europa,
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an icy moon of Jupiter, have conditions that could support some sort of living thing.
People use yeast, one kind of unicellular organism, to make bread and beer. Others help us
by eating harmful bacteria and are food for fish and other animals. At least one kind of
unicellular organism can cause illness in people. Amoebic dysentery, whose main symptom is
bloody diarrhea, is transmitted by water containing one type of amoeba. It is well known as
traveler's dysentery, or Montezuma's Revenge, particularly in Mexico. Liver infection and
abscesses can occur also. It can be treated with antibiotic drugs.
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Unicellular organisms are all around us. They have lived on Earth for many millions of
years and have developed unique ways to survive. Although small, they are complex and
beautiful. The next time you look at pond water, just think what you might discover there!
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Copyright © 2015 edHelper
Name _____________________________
Date ___________________
Unicellular Organisms
1. What are unicellular organisms?
Plants with many cells
Animals with many cells
Protozoa, algae, fungi, or bacteria
made of only one cell
Not alive
3. How long do scientists think unicellular
organisms have lived on Earth?
3.8 million years
3.8 billion years
Millions of years
3.8 trillion years
5. What is the advantage of having a spiral
shape?
Can get more food
Keeps it from drying out
Easier to move
More surface area for chemical
processes
7. What is one kind of unicellular organism
that is helpful to people?
Amoeba
Paramecium
Yeast
Euglena
2. What does unicellular mean?
Many cells
Unicycle
One cell
Multicellular
4. What is the advantage of having a spherical
shape?
Keeps it from drying out
Easier to move
Can get more food
More surface area for chemical
processes
6. Where have extremophiles been found?
In Antarctica and the deep sea
On the sun
On the moon
On Mars and Europa
8. What does pseudopodia mean?
False name
Made-up name
False feet
Encyclopedia