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1.13
Protists
If you look in to a drop of pond ivater, you
will find an incredible collection of profists.
Almost anywhere there is water, even in moist
soil or in rotting leaves, you will Find protists.
Unlike bacteria, protists have a nucleus and
contain organdIes such as mitochonclria,
rihosomes, and lysosoines.
Unicellular Organisms
are a multicellular organism. You have many specialized cells that
work together to carry out all of life’s functions. I—Towevcr. many living
things are composed ofjust one ceLl. These unicellular organisms,
referred to as microorganisms or microbes because they arc only visible
tinder a microscope, must also carry out all of life’s functions. The
single cell is responsible for feeding, digestion. excretion, and
reproduction.
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The Importance of Microorganisms
Most people become aware of microorganisms when they get sick.
However, it is unfair to think of microorganisms just in terms of
disease. It’s true that they cause many diseases, but most are harmless
and many are even helpful, as you can see in Figure 1. Dairy products
such as buttermiLk, cottage cheese, and yogurt are produced by the
action of microorganisms.
Ba cteri a
Bacteria (singular form is hndthuni) are among the most prLmitnr and
also the most plentiful organisms on the planet. They are said to he
very successful because they have survived and changed little over
several billion years (Figure 2). Some, like plants, can make their own
food. Others are parasites. (Parasites can live by invading the body of
an animal or a plant.) Some bacteria can even live with little or no
oxygen. There are bacteria in every Earth environment, even in hot
springs. Bacteria are clifThrent from animal and plant cells in that
they have no nucletis, no mitochondria, and no ribosomes.
pili: These hairlike structures help bacteria
to attach to each other and to surfaces.
They also help bacteria to move.
chromosome: The genetic
material of bacteria is organized
in one chromosome. There is no
nucleus.
cell membrane: Regulates
movement of materials
into and out of the cell
A typical bacterium
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Plantlike Protists
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Each droplet swayed to
me air Curing a sneeze
could contain thousands
of microorganisms.
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Mcroorganisrns
0 decompose
dead plants
and animals into chemical
building blocks that can
be recycled by plants into
food for humans and
other animas.
In.
Some mcroorganisms make
us sick, but without me
others we could rot survive.
Diatoms
Diatoms are found in both fresh and salt
water. They contain chlorophyll and can make
their own food. Diatoms are encased in two
thin shells joined together. Figure 3 shows
some diatoms.
Euglena
Euglena (Figure 4)is like both a plant anti an
animal cell. If there is lots of sunlight, euglena
acts like a phmt and makes its own food. With
reduced sunlight, euglena acts like an animal
and begins feeding upon snmller cells.
Each species of diatom has a unique shape.
They all have symmetrical grooves and pores.
flagellum: Helps the cell to move
eyespot: Directs euglena
toward the light
mitochondria: Provide the energy
for the flagellum and other needs
Golgi apparatus:
Stores chemicals
flagellum: Some bacteria
have whiplike tails to help
them move.
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chloraplasts: Contain chlorophyll,
the green pigment used to make
food by photosynthesis
contractile vacuole:
Expels excess water
a
cell wall: Provides
rigid support
capsule: A sticky coating surrounds disease-causing
bacteria. The capsule makes it difficult for animals’
white blood cells to destroy these bacteria.
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E.g;era as :e..tures of both
plant and animal cells.
nucleus:
Contains the
genetic material
pellicle: A firm covering that
surrounds the cell membrane.
Unlike plant cell walls, this
covering is flexible.
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