Reading 1

Unit 3- Reading 1

Page 34

Harmful and helpful bacteria

One day in 1676, a Dutch scientist named Antony van Leeuwenhoek looked through a microscope. He reacted with surprise. Something appeared that no one had ever seen before. He saw bacteria.

As he proceeded to watch, the things moved. They were so tiny that he could see them only through a microscope. He did not know what they were. He did not know where they came from. Today, over 350 years later, scientists know that the world is filled with bacteria. Scientists know that bacteria can harm and can help humans.

Bacteria—tiny living things—exist everywhere in the environment They exist deep under the ground. They exist in oceans and lakes. They exist inside of plants and animals. They exist on people’s hands and in their noses. People cannot see them. Yet bacteria have many effects on humans.

There are many kinds of bacteria. Some are harmful and others are harmless Many bacteria actually help us.

PROBLEMS WITH BACTERIA

Sometimes the word germs is used to describe harmful bacteria. Germs can cause terrible diseases such as cholera and tuberculosis. Cholera bacteria live in dirty water. If a person drinks the dirty water, the bacteria will infect his digestive system.

He will suffer terrible stomach pains. Some diseases easily transfer from one person to another. For example, someone who has tuberculosis bacteria in her lungs can transfer the disease if she coughs or sneezes. The bacteria come out of her mouth or nose and proceed into the surrounding air. People who breathe the air will breathe in the harmful bacteria.

Often foods have germs growing on them or inside of them.

Eating the food could make people sick. However, there are ways to prevent getting sick. For instance, washing fruits before eating them will wash away many harmful germs. Heat is another way to destroy harmful bacteria. Cooking meat for a long time will make it safe to eat.

BENEFITS OF BACTERIA

Not all bacteria are harmful. Some bacteria help humans in many ways. For example, millions of good bacteria exist in the body’s digestive system. They help change the food we eat, so our bodies can use the vitamins in the food. Also, good bacteria are needed to make certain foods, such as cheeses and yogurts.

Many bacteria also help the environment.

For example, bacteria help break down dead plant material, such as fallen leaves, so it can mix with the soil. Bacteria that exist in the oceans help in several ways. For example, they become food that is eaten by tiny fish. Then the tiny fish become food for big fish. When you catch a big fish, it becomes food for your dinner.

Another way that bacteria help is by cleaning up oil spills from ships. Also, they help clean up human waste that rain carries into the oceans.

Our world is filled with bacteria, but not all are harmful. In fact, some help us.