You have seen several kinds of plants and animals. However, there are other living organisms around us which we normally cannot see. These are called microorganisms or microbes. Micro means tiny and organism means a living creature. Microorganisms or microbes are so small in size that they cannot be seen with the unaided eyes. Some of these, such as the fungus that grows on bread can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.
Plants are unable to take from the soil the nutrition they need without microbes working in the soil. Microbes are alive and must have nutrition to survive, and that nutrition comes from organic matter. As they consume the nutrients they need, microbes create foods like nitrogen, carbon, oxygen, hydrogen and trace minerals for our plants. It is the microbes that convert the minerals in the soil into a form our plants can use to grow and produce food and flowers for us. Most of the times when they are in the right place the majority of microorganisms are not harmful to people and often do a lot of good such as breaking down waste and making bread. There is a huge variety of microorganisms. They can work alone or in colonies. They can either help us or hurt us. Most importantly, they make up the largest number of living organisms on the planet.
Microorganisms are classified into five major groups:
Bacteria are microscopic, single-celled organisms that exist all around you and inside you. Although they can cause sickness and disease, they are very important to life on Earth. We depend on bacteria to help in the digestion of food, for plant growth, and to help us make foods and medicines. Bacteria are an important part of the soil. They are able to capture some nutrients that plants cannot. When living things die, bacteria play a very important role as decomposers, bacteria, and fungi feeding on and breaking down plant and animal matter. Without these decomposers, the bodies of all organisms that have ever lived would still remain. This would be messy. When bacteria break down the dead organisms, they release substances that can be used by other organisms in the ecosystem.
Bacteria can affect our bodies in several ways. Harmful bacteria can make us sick, but fortunately, our bodies will fight back. When Streptococcus bacteria give us strep throat we can take medicine to help us get well faster. Some bacteria always live in our bodies. They are found in digestive systems and help digest food. Other bacteria are in our food. When you eat yogurt or cheese, you eat bacteria.
Bacteria are the smallest microorganisms.
Fungi are microorganisms that are neither plant nor animal, yet have characteristics of both, and absorb food from whatever source they are growing on. A common fungus is a mushroom. It looks like a plant but is not green. Mushrooms cannot make their own food and must live on a food source. Some are poisonous, and only an expert can identify them. Another fungus is yeast which is used to make bread rise and give it flavor. Athlete’s foot is caused by a fungus. Some types of fungi rot the wood in homes. Fungi also like warm moist places to grow. A good way to prevent fungus is to keep things, like your toes dry.
Protozoans are microscopic organisms that usually live in water. They move through the water with tiny hair-like arms called cilia. The cilia are located all around the sac-like body of the protozoa and wave back and forth to move the protozoa through the water. Protozoa are an important food source for many pond creatures. Some protozoans are harmful to people. You may have heard that it is not a good idea to drink water from a stream. Streams sometimes contain a protozoan called Giardia that can make you sick.
Algae are a type of single-celled organism that usually live in water and can produce their own food. Some algae are very large, while others are microscopic. Algae can be red, brown, yellow or green. Some of the largest algae are kelp. They can grow to be 60 meters long. Algae are an important part of the ocean’s ecosystem. They provide food for fish, whales and many other sea animals.
Viruses are very simple microorganisms, they can’t do much by themselves. They need a host (another living organism) that gives them everything they need to work. They are parasites which means they can only survive inside the cells of other living things. They are acellular microorganisms which mean they are not composed of cells. Common ailments like cold, influenza (flu) and most coughs are caused by viruses. They can cause infectious diseases such as chicken pox or measles; and other serious diseases like polio. Diseases like dysentery and malaria are caused by protozoa (protozoans) whereas typhoid and tuberculosis (TB) are bacterial diseases.
