The Kingdom of Protists
Cell Structure
Protist cells do have a nucleus, and it is surrounded by a nuclear membrane.
They are called eukaryotes, which means “true kernel”. (The “kernel” is the
nucleus.) Protists also have cell organelles that help the nucleus perform all the life
processes. For example, they have mitochondria, which help the organism use its
food. They may also have chloroplasts, which help producers make their own food.
Number of Cells
Many protists have only one cell, but some of them have many cells. The
groups of cells do not, however, form tissues or organs.
Kinds of Movement
Some protists do not move at all, but many of them are able to move. Some
protists use pseudopodia, or false feet. The cell in this type of protest is able to
change its shape. It is able to extend some of the cytoplasm to make a fake foot or
two. The feet are able to push or pull the cell along.
Other protists move using tiny hair-like structures called cilia. The cilia are
found on the outside of the cell. They are able to move very quickly back and forth,
moving the protists along through water for another liquid.
Finally, some protists move using flagella. These are simple, whip-like
structures that propel the protist through its environment.
Nutrition
As we found with monerans, some protists are producers. This means they
are able to capture the Sun’s energy and make their own food. Other protists are
consumers; they use other organisms as their food sources.
Any organism that has the above specific characteristics is a protest. Now we
will take a closer look at three groups of protists: those that are plantlike, those that
are animallike, and those that are funguslike.
Protists: The Middle Kingdom
Aristotle developed the two-kingdom system of classification. For many
years, and organism was either classified as a plant or an animal. As scientists
developed better tools for investigating and learning more about organisms, it
becomes increasingly difficult for them to use Aristotle’s system. They were too
many organisms that really did not belong in the plant group, and they really did not
belong in the animal group. A new system had to be developed.
Ernst Haeckel, a German biologist, was the first scientist to suggest a “middle
kingdom”. The protest kingdom became the place for organisms that were not quite
plants and were not quite animals. At first, this kingdom was not clearly defined,
but scientists kept investigating and learning more and more.
As scientists have continued to do their research, they have finally defined
the protest kingdom and its specific characteristics more carefully. Protists are
organisms that are a bit more complex than monerans, but they are not as complex
as plants and animals. As you have already learned, these organisms may be singlecelled, or they may be multicellular. The many-celled protists do not, however,
form tissues or organs like more compete organisms do.
Remember that each protest cell has a nuclear membrane. The cells also have
organelles to help them complete all their life processes. In this way, they’re more
complex than their “cousins”, the monerans.
Protists, for the most part, line in moist or wet environments. They either
make their own food, or they use monerans as their food source. They use cilia
pseudopodia, or flagella to move around in their watery homes.
At the present time, scientists have developed three groups of protists. They
have plantlike protists, which may be called algal protists or algae. They also have
animallike protists, which are often called protozoans. The third group is known as
the funguslike protists. Let’s take a closer look at each of these groups.
Plantlike Protists: Algea
Plantlike protists are an important part of our world. They are producers,
which means they make their own food. At the same time, they make oxygen and
release it into the environment. As we know, many organisms depend on oxygen to
stay alive. Algea are doing their part to keep us breathing properly.
Algea also use carbon dioxide in the process of photosynthesis. They are able
to absorb much of the carbon dioxide that is released when we turn fossil fuels, such
as coal, oil, or natural gas. They combine this carbon dioxide with water to make
their food and the extra oxygen they release. In this way, algae help reduce the air
pollution levels.
Algae are considered the basis of many aquatic food chains. Remember that
they prefer to live in wet or moist areas. They make their own food and often
become a food source for other organisms. Further up those food chains may be
many of the lunches or suppers that we enjoy! Without algae, the other organisms
could not survive, and we would have fewer food choices.
There are many different kinds of algae, so they are not easy to describe.
They range from single-celled organisms to multicellular organisms. They come in a
variety of colors and shapes. Although they are small, they are important in our lives
and in our environment.
Animallike Protists: Protozoans
Plants are producers. Plantlike protists are producers, too. Animals are
consumers. What about animallike protists? You guessed right. Animallike protists
are consumers, too. They are often called protozoans. Proto means “first” and zoa
means “animals”. Protozoans are the simplest organisms that have some
characteristics like animals.
Scientists believe there may be as many as 100,000 species of protozoans.
Most of these species have only one cell. They can be found in a variety of
environments, including in water and soil. They can also be found inside living and
dead organisms. Many protozoans are parasites. A parasite is an organism that
lives in or on another organism causing that host organism some harm.
With so many species of protozoans, scientists needed to have a way to
classify them into smaller groups so they could study them more carefully. They
looked carefully at the way the protozoans move. They divided protozoans into four
smaller groups based on their kind of movement. You will study more about that in
coming years.
Funguslike Protists
The final group of protists are the funguslike protists. These organisms do
not make their own food, nor do most of them eat other organisms. To get their
energy, these simple organisms decompose other matter and absorb the nutrients
into their cells.
Scientists have classified funguslike protists into several smaller phyla. We
will tke a look at slime molds, water molds, downy mildews, and white rusts.
Slime Molds
With a name like that, you might think that slime molds are pretty awful. In
reality, they are pretty cool. Slime molds are funguslike protists that prefer cool,
moist, and shady areas. They can be found on logs, in dead leaves on mulch, and
occasionally on lawns, when conditions are right. They come in many beautiful
colors including yellow, white, black, red, purple, and pretzel brown. They spread
across the top of their food supply, making interesting patterns and webs. When
they dry up, they may become powdery or they may look like dried up mushrooms.
Slime molds have some characteristics that are like other protists. They are
able to move with pseudopodia during some phases of their life cycles, much like
amoeba. Slime molds also have some characteristics that make them like fungi.
They reproduce with spores, much like a fungus. Slime mold, however, do not have
cell walls made of chitin, so most scientists classify them with protists.
Water Molds, Downy Mildews, and White Rusts
Last night I wanted a baked potato for dinner. I went to the pantry and
pulled out a potato. Uh,oh! I noticed a fuzzy, white growth on the potatoes. What
was I looking at? Water mold! This protist was largely responsible for the terrible
potato famine that struck Ireland in the 1840s. Much of Ireland’s potato crop was
ruined by water mold, and as many as 1,000,000 of the Irish people starved. Many
others left Ireland, emigrating to America and other parts of the world. Water mold
can still be a problem today for potato growers, in Ireland and in the United States,
as well.
Water molds, downy mildews, and white rusts are another phylum of fungus
like protists. They prefer to live in water in moist areas. Some of them actually
digest plant and animal matter, while others break down matter and absorb the
nutirents. Some of the members of this group are parasites found on plants and
others feed on dead fish. If you have an aquarium, you may have noticed water
molds attacking and killing fish.
Funguslike protists have some characteristics that are like fungi. However,
they have more characteristics that are like protists, so most scientists classify them
in this kingdom. They all have roles to play in our environment. Some of them are
helpful to us, while others are harmful. It is important to understand as much as
possible about each of them so we can get a better idea of just how our world works.