Microscopic life

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."