There is a world all around you that you
cannot see. Billions of tiny creatures slither and slide over tables and
floors. They float and wiggle in drops of water. They stick to your skin.
Sometimes they get in your eyes, nose, and throat.
You can see most of these tiny things only
if you put them under a microscope. These tiny life forms are called
microscopic life or microorganisms. They are also called microbes. Most
microbes are made of just one cell. Your body, by contrast, has billions of
cells.
MANY KINDS OF MICROBES
There are thousands of different kinds of microbes.
Microbes called bacteria are the smallest living things. Bacteria live almost
everywhere: on land, in water, and even inside you.
Some microscopic life forms are like plants. Tiny
diatoms are microbes that live in lakes and the ocean. Diatoms soak up sunlight
and use its energy to make food, just like plants.
Some microscopic life forms are more like animals.
Protozoa such as the amoeba and paramecium are animal-like microorganisms. An
amoeba can move by changing the shape of its body. It sticks out a pseudopod,
or false foot. A paramecium is covered with tiny hairs. It waves its hairs
rapidly to swim.
Viruses are another kind of microbe. Viruses
sometimes act like living things and other times act like nonliving things.
Viruses sometimes live in the cells of plants and animals. Inside a cell, a
virus reproduces like a living thing. The virus uses the cell to make many
copies of itself. Viruses are too small to see with an ordinary microscope. You
need a powerful electron microscope to see a virus. Outside of a plant or
animal cell, a virus is like a nonliving thing.
ARE MICROBES HARMFUL?
Some microbes are harmful. Some microbes are
helpful. Protozoa called plasmodium cause a serious disease called malaria.
Some bacteria and viruses can make you sick. We sometimes call these microbes
germs.
Harmful bacteria can make food spoil. You can get
sick to your stomach if you eat the food. Some harmful bacteria can cause an
infection in a cut or sore. Others cause pneumonia, strep throat, tuberculosis,
typhoid fever, and other diseases.
Viruses cause chicken pox, measles, flu, and common
colds. They also cause very serious diseases such as rabies, polio, and
acquired immunodeficiency syndrome (AIDS).
WHAT DO HELPFUL MICROBES DO?
Harmless bacteria in your body compete with harmful
germs. Harmless bacteria compete for food and keep the harmful germs under
control. Some bacteria in your body help you digest your food.
Some bacteria in the soil help plants grow.
The bacteria break down dead plants and animals into chemicals that plants can
use. Some bacteria take nitrogen gas out of air and water. They change the
nitrogen so that plants can use it to help make food.
Diatoms are important food for fish. Diatoms are part of
the plankton that floats on the ocean. Plankton is made up mostly of
microscopic life forms. Many kinds of animals that live in the ocean eat
plankton.
WHO DISCOVERED MICROORGANISMS?
A Dutch scientist named Antoni van Leeuwenhoek was
the first person to see microorganisms. He invented a microscope more powerful
than any that had previously been made. He saw microbes under his microscope in
1676. He called the microscopic organisms “animalcules.”