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How are microorganisms useful to us?

Class 8 ScienceNCERT chapter: The Invisible Living World: Beyond Our Naked Eyeइसे हिंदी में पढ़ें

Exam-ready answer

Microorganisms are useful in many ways. Lactobacillus bacteria turn milk into curd, and yeast makes bread dough rise. Decomposer microbes break down dead plants and animals and return nutrients to the soil. Rhizobium in the root nodules of pulse plants fixes nitrogen. Some microbes are used to make medicines such as antibiotics, and to make vaccines.

Explanation

Microorganisms are living things too small to be seen with the naked eye, such as bacteria, fungi, protozoa and some algae. In the kitchen, a little curd added to warm milk brings Lactobacillus bacteria, which multiply and change the milk into curd. Yeast, a fungus, respires and releases carbon dioxide gas, which makes dough for bread and idli or dosa batter puff up.

In nature, bacteria and fungi act as decomposers. They break down dead leaves, animal remains and kitchen waste into simple substances, which enrich the soil. This is how compost is made. Rhizobium bacteria living in the root nodules of leguminous plants like peas and gram take nitrogen from the air and convert it into a form that plants can use.

Microbes are also used in medicine. Antibiotics like penicillin are made from certain fungi and bacteria; they kill or stop the growth of disease-causing bacteria. Vaccines are prepared from dead or weakened microbes. Microbes are used to clean sewage water, and some are used to make products like vinegar. So most microbes are not harmful, and many are our helpers.

Points to remember

  1. Lactobacillus converts milk into curd; yeast makes dough rise by releasing carbon dioxide.
  2. Decomposers (bacteria and fungi) break down dead matter and return nutrients to the soil.
  3. Rhizobium in root nodules of leguminous plants fixes atmospheric nitrogen.
  4. Antibiotics such as penicillin are obtained from microorganisms.
  5. Vaccines are made from dead or weakened microbes and protect us from diseases.

Exam tip

Write the uses under clear headings such as food, soil, medicine and environment, and give one named microorganism as an example under each heading.

Questions students also ask

Why does dough rise when yeast is added?
Yeast feeds on the sugar in the dough and respires. During this process it releases carbon dioxide gas. The gas forms tiny bubbles that make the dough swell and become soft and spongy.
Why should antibiotics be taken only when a doctor advises?
Antibiotics act on bacteria, not on viruses like the common cold. Taking them without need or leaving the course midway can make bacteria resistant. That is why they should be taken only when a doctor prescribes them.
How do microorganisms increase soil fertility?
Decomposers turn dead plants and animals into nutrients that mix with the soil. Nitrogen-fixing bacteria like Rhizobium add nitrogen compounds to the soil. Both make the soil richer for the next crop.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.