Unit D5 - Microbes


Unit D5


We know about large plants and animals like trees and horses, and small ones like grass and mice, and very small ones like mosses and ants, but there are many other living things even smaller then that, so small that we cannot see them with the naked eye. They are called microbes. This whole world of tiny living things is very important in the environment, so we must learn to understand, appreciate and respect them.

There are many kinds of microbes, and they are everywhere around us, in the soil, in the air, on our skins and even inside of us. Some microbes are tiny plants called algae that usually live in the water or on land. They make their food with energy from the sun just like bigger plants. When they are very numerous, they may colour the water green or brown, or they may appear as slimes or scums. The greenish black that often stains the outside of concrete buildings in the tropics comes from algae. Algae may be green, blue-green, brown, yellow-brown or even red or orange, like the alga that sometimes grows on the trunks of coconut palms near the sea.

There are also tiny animals or protozoa of many kinds that swim or crawl around and eat things like algae and other animals. Since most of them are colourless, they are hard to see without some kind of magnification.

The bacteria or germs are even smaller than the algae, and there are billions and billions of them everywhere. They live by dissolving and breaking down any kind of organic matter, which includes anything that is or was part of a living thing. Thus they break down anything that is dead, and sometimes they do not wait for it to be dead, which is often how things get sick. It is usually bacteria that cause milk to go sour or food to spoil. Even though a surface may look clean, it has bacteria on it unless it has been sterilised (made clean of all bacteria) by heating, boiling or the application of alcohol or an antiseptic (a chemical that kills bacteria).

Another important group of microbes are the fungi, which grow like plants but get their food by breaking down dead material. They include the moulds and mildews which are responsible for rotting and decay. Mushrooms are the fruiting bodies of certain kinds of fungi.

There are three important kinds of activities that microbes carry out in the environment:

1. Decomposers

These microbes are an essential part of all ecosystems, because they decompose or break down dead material and keep it from accumulating. If something did not break down the dead leaves in a forest, they would pile up higher and higher until the trees were buried under them. When the decomposers break things down, they release the materials of which these things were made, particularly the nutrients, which are then available to be taken up by plant roots and used again. If the nutrients were not released, they would eventually all be tied up in dead material, and then nothing else could grow. Sometimes the decomposers create a problem when they rot or spoil things faster than we would like.

2. Symbionts

Sometimes microbes are actually helpful to plants and animals in a relationship called symbiosis because each one helps the other. For instance, there are certain fungi in the soil which grow attached to the roots of trees and which help the tree to absorb water and nutrients from the soil. This help is so important for some trees that they cannot grow without their special fungus.

Only certain bacteria and blue-green algae (cyanobacteria) are able to fix nitrogen from the air and make it available as a nutrient to plants. In a few plants like the legumes, the roots have special swellings, called nodules, where nitrogen-fixing bacteria can live under good conditions inside the roots and make nitrogen nutrients for the plant.

Animals like corals and giant clams have one-celled algae (tiny plants) living inside their bodies; the animals give the plants shelter and nutrients and expose them to the light, and the plants make food for the animals. Then there are animals like cows and termites that have special bacteria living in their stomachs to help them digest food in the grass and wood that they could not use otherwise.

3. Disease germs

There are always many kinds of microbes on and in our bodies, but most of them do not hurt us, and a few are even helpful. Unfortunately, some microbes are much more dangerous, and want to live off of us or of other living things before we are dead. Some may even try to kill us to get more food. As they multiply in our bodies they make us sick. Our bodies have some defences against these disease germs, but sometimes they are not enough, and we need the help of medicines to overcome the germs and get well again. Antibiotics, for instance, are special poisons against microbes, just as insecticides are poisons against insects. Doctors sometimes must give us these strong medicines to help our body get rid of a dangerous disease germ, but they must be used with care or they can upset the body’s balance in other ways.

Living with microbes

In thinking about the environment, we must remember that the microbes are always there even if we cannot see them. Often they are useful, but sometimes they are dangerous, and we must learn how to be careful and control them. Microbes that cause disease are often spread from one person to another, making many people sick. When a person is sick, there may be many disease germs in his mouth or in his wastes. If he sneezes on his hand, there will be germs on his hand. If he touches a child, the sickness could pass to the child; if he touches a loaf of bread, the germs could pass to anyone who eats the bread.

Suppose a person has been sick in the bush. An animal might pick up his germs and bring them back to the village. Pigs, rats, cockroaches and flies, all may carry germs from dirty or unsanitary places and put them on food or in places where children play. This is why if a place is clean there is less chance of spreading sicknesses.

Germs are often spread through dirty or contaminated water. Imagine a bucket that everyone uses. It may be set on the ground where dirty pigs have been walking, or be used for washing dirty clothes or a sick babies' diapers, then it may be lowered into a well or cistern to get water for washing. The germs on the sides and bottom will get into the water, and then can be given to anyone drinking the water or eating food or from plates that have been washed in it. Since you cannot see germs, they may be there even if something looks clean.

There are things that can be done to control the harmful effects of germs or to keep them from spreading. Microbes are always waiting to break down anything that is lying around, like our food, for example. Since microbes usually grow faster when it is warm, food spoils faster (from attack by microbes) in warm weather. If the food is put in a cold place like a refrigerator, the microbes grow more slowly, and the food will keep several days. The colder it is, the longer the food can be kept without spoiling. In a very cold freezer, the microbes can hardly grow at all. In the same way, enough heat can kill microbes. Boiling water for 20 minutes will kill the germs in it, or in any food put in it. The food in cans does not spoil because the cans were heated in the cannery to kill all the microbes inside. Boiling baby bottles and nipples, and any water put inside them, will sterilize them and kill all the germs, since babies are still weak at fighting germs and get sick very easily.

There are also chemicals that can be used as disinfectants to kill microbes, including chlorine bleach, alcohol, and the antiseptics used to treat cuts and other injuries which might otherwise let microbes into the body. Washing with soap or detergent can reduce but not eliminate microbes. If someone is sick and there is a danger of contamination, then a disinfectant can be used to keep the germs from being spread.


Where are microbes found? Can you name some of the places?

What are some of the important kinds of microbes?

What do they do?

How do microbes contribute to nutrient cycles?

What happens to something that dies?

What would happen if there were no microbes?

What are some ways that microbes can be helpful?

Why are microbes sometimes dangerous or harmful?

How do medicines like antibiotics work?

What are some ways that germs or other harmful microbes can be spread in the house? In the village?

What can you do to keep microbes from spreading if someone in the house is sick?

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Last updated 1 January 2008