Ameobas
Amoebas, like all protists, are single-celled organisms. Cells are the building blocks for all life forms. "Single-celled"
means that amoebas have only one cell for their entire body. A human body has more cells than you can count.
The inside of an amoeba is a jelly-like fluid called cytoplasm. Bits of food and other materials float around in the
protoplasm.
Amoebas are so tiny that you need a microscope to see them. They live in water, including lakes, ponds, streams, rivers,
and puddles. Some can even live in the bodies of animals.
The most important part of an amoeba might be the pseudopod (pronounce it "sudopod").
The psuedopod is used to help the amoeba move, and also to eat. It is a part of the amoeba's body that it can stretch
out and pull itself with. Or, to eat, the amoeba stretches out the pseudopod, surrounds a piece of food, and pulls it into
the rest of the amoeba's body.
Amoebas reproduce (make more amoebas) by a process called binary fission. This means that one amoeba can split in
half and make two identical new amoebas
Amoebas eat algae, bacteria, other protozoans, and tiny particles of dead plant or animal matter.
They spend most of their time attached to the bottom or to plants. Sometimes they float freely in the water. They do
this as a "swarm." All the amoebas of the same species will unattach from the bottom or plants and float around until
they land in a new place and re-attach.
Animals that eat amoeba include plankton feeders, such as mussels and water fleas.
Euglena
Euglena are small organisms in the Protist Kingdom. Euglena gracilis is just one of many species of Euglena. They do not
have common names like birds or trees, so we have to refer to them by their scientific name.
Euglena are interesting because they are a sort of combination of plant and animal. They can make their own food like a
plant, but they can also eat other things, like an animal. They can also swim and move. Scientists argued for years about
which Kingdom to put them in, Animal or Plant? Right now they are in neither; most scientists put them in the Protist
Kingdom with other microscopic organisms, such as amoeba and paramecium.
Euglena gracilis and other euglena are green because they eat green algae. They keep the algae inside their bodies and
use it to make their own food. These green parts inside the Euglena's body are called chloroplasts.
A euglena's body is only one cell, so they are very small and you must use a microscope to see them. Sometimes, since
they live in water, if there are millions of euglena together, they form a mat on the surface of a pond or marsh that you
can see. It looks slimy, a lot like algae. Some people say it looks like "pea soup." It gets in swimming pools too, if they are
not cleaned regularly. If you've ever seen water in a marsh that looks red, it's from many euglena. Some species have
chemicals in them that make them red. Euglena gracilis is not one of those species.
Euglena gracilis has a long hair-like thing that stretches from its body (see top picture). You need a very powerful
microscope to see it. This is called a flagellum, and the euglena uses it to swim. It also has a red eyespot. Euglena gracilis
uses its eyespot to locate light. Without light, it cannot use its chloroplasts to make itself food.
In order for Euglena gracilis to make more Euglena gracilis it will complete a process called mitosis. That means it can
split itself in half and become two Euglena gracilis. It can only do this if it is well-fed and if the temperature is right.
Euglena gracilis can reproduce better in warm temperatures. The picture below shows an Euglena gracilis splitting into
two. Can you see both eyespots?
When Euglena gracilis doesn't have enough light to make its own food, it looks for other things to eat. Swimming
around, it preys on other tiny organisms, such as amoeba and paramecium.
Predators of Euglena gracilis and other euglena include: baby fish, water fleas, mussels, and frogs and salamanders
(tadpoles and larval stages).
One way that Euglena gracilis can get from one body of water to another is birds. Water birds, like ducks, geese, and
herons get mud stuck to their feet. Euglena gracilis that are in the mud can get a free ride to a new pond, river, or
marsh.
Paramecium
Paramecium, like all protists, are single-celled organisms. Cells are the building blocks for all life forms. "Single-celled"
means that a paramecium has only one cell for its entire body. Most plants and animals have more cells than you can
count.
The inside of a paramecium is a jelly-like fluid called protoplasm. Bits of food and other materials float around in the
protoplasm.
Paramecium are so tiny that you need a microscope to see them. They live in water, including lakes, ponds, streams,
rivers, and puddles. Some can even live in the bodies of animals or in moist soil.
It may be difficult to see in the pictures, but Paramecium have tiny hair-like things, called cilia, all around the outside of
their cell. Cilia are important, because they are how Paramecium move. By beating the cilia back and forth, the
Paramecium can move through the water. Protists with cilia, such as Paramecium, move much faster than other protists.
Like other protists, Paramecium usually attach themselves to the bottom of the pond or stream, or to a plant.
Sometimes they "swarm." That means they all let go and swim around until they find a new place to attach.
Paramecium reproduce by a process called binary fission. This means the Paramecium can split in half and become two
new Paramecium.
Paramecium eat algae, bacteria, other protozoans, dead plant and animal matter, and other tiny animals. They have
something similar to a mouth, called a cytostome, to let food items into their bodies.
Some types of green algae can live inside the protoplasm of a Paramecium. Here, it takes nutrients from the
Paramecium, but it also gives important nutrients as well.
Paramecium are eaten by other protists, as well as animals that eat plankton (microscopic organisms in the water), such
as water fleas and mussels.
Bacteria
Bacteria can be found virtually everywhere. They are in the air, the soil, and water, and in and on plants and animals,
including us. A single teaspoon of topsoil contains about a billion bacterial cells (and about 120,000 fungal cells and
some 25,000 algal cells). The human mouth is home to more than 500 species of bacteria.
Some bacteria (along with archaea) thrive in the most forbidding, uninviting places on Earth, from nearly-boiling hot
springs to super-chilled Antarctic lakes buried under sheets of ice. Microbes that dwell in these extreme habitats are
aptly called extremophiles.
Good bacteria vs. bad bacteria
Not all bacteria are bad. In fact, some are rather good for you. But the line could be a thin one. So, what should you
know?
The human body plays host to a number of micro-organisms, most of which are our friends. This is nothing to be grossed
out about. In fact, the phenomenon of living in close physical association with other organisms ("symbiosis") is as
common as life itself.
The bacteria that live in the colon
The colon has the largest microbial community in the body. In this part of the body, the bacterial population usually
doubles once or twice a day. Many of these bacteria are, of course, also excreted during the course of the day, so that a
delicate balance is maintained.
Under normal circumstances, the microbial community in the colon - which includes more than 300 different species of
micro-organisms - regulates itself. Competition between the different micro-organisms, and also between the microorganisms and their human host, serve to maintain this status quo.
These micro-organisms normally prevent infection and proliferation of "bad" bacteria (pathogens like Salmonella and
clostridia, for instance), and have a positive effect on nutrition.
However, the intestinal environment of the colon can very easily be disturbed. This may change the delicate balance of
normal micro-organisms in the colon greatly. Several factors, like stress, altitude changes, starvation, parasitic
organisms, diarrhoea, and use of antibiotics, could contribute to such a disruption.
Boosting the "good" bacteria
When the balance of microbiota is disturbed, one can become susceptible to disease. In these circumstances, boosting
the numbers of "good" bacteria present in the gastrointestinal tract can be particularly useful. This is where probiotics
come into play.
Probiotics are microbial foods (e.g. yoghurt with live AB cultures) or supplements (e.g. chew tablets or capsules) that can
be used to change or improve the intestinal bacterial balance to boost the health of the host.
The most common forms of probiotics include Lactobacillus and bifidobacteria. These good guys thwart the overgrowth
of toxic bacteria by competing for attachment sites and nutrients in the gastrointestinal tract.
Lactobacillus and bifidobacteria also produce organic acids that reduce the intestinal pH and retard the growth of "bad",
acid-sensitive bacteria.
Fermented dairy products, like live culture yoghurts, kefir (milk drink flavoured with salt or spices) and commercial
probiotic preparations, contain Lactobacillus, bifidobacteria, and other forms of beneficial bacteria.
Other forms of fermented foods, such as sauerkraut (white cabbage cut finely, salted and fermented in its own liquid),
miso (a thick paste made from fermented and processed soy beans) and tempeh (a dish made from split soybeans and
water) may also be cultured with Lactobacillus strains.
However, the potency and number of live organisms in commercial products may vary greatly. And many manufacturers
are finding it difficult to overcome technical problems, especially in terms of keeping the micro-organisms alive under
unfriendly conditions.
"But probiotics are an asset to the consumer," says Prof Trevor Britz from the Department of Food Science at the
University of Stellenbosch, and these foods should form part of a healthy, balanced diet.
Take note of prebiotics too
When it comes to intestinal health, one also needs to consider prebiotics - non-digestible food products that stimulate
the growth of "good" bacteria already present in the colon.
Prebiotics include foods that contain substrates, like dietary fibre and fructo-oligosaccharides, that nourish the beneficial
micro-organisms in the gut.
It is therefore essential to include enough fibre in the diet by eating fruit, vegetables and whole-grains. Food sources of
the fructo-oligosaccharides - which should also form part of a healthy diet - include honey, beer, onion, asparagus, rye,
banana, maple sugar and oats. - (Carine van Rooyen)
Sources:
Mahan, LK, et al. Krause's Food, Nutrition, & Diet Therapy, 10th Edition (p.278). Saunders, 2000.
Prescott, LM, et al. Microbiology, 4th Edition (p. 566-578). The McGraw-Hill Companies, Inc., 1999