MAKING OF CURD AND BREAD

MAKING OF CURD AND BREAD

You have learnt in Class VII that milk is turned into curd by bacteria.  Curd contains several micro- organisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd. Bacteria are also involved in the making of cheese, pickles and many other food items. An important ingredient of rava (sooji ) idlis and bhaturas is curd. Can you guess why? Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.

Activity 2.3:

*   Take ½ kg flour (atta or maida), add some sugar and mix with warm water.

*   Add a small amount of yeast powder and knead to make a soft dough.

*   What do you observe after two hours? Did you find the dough rising?

Figure 2.6:

Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume (Fig. 2.6). This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.

Source: This topic is taken from NCERT TEXTBOOK

COMMERCIAL AND MEDICAL USE OF MICROORGANISMS

COMMERCIAL AND MEDICAL USE OF MICROORGANISMS

Commercial use of microorganisms

Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice, crushed fruit juices, etc.

Activity 2.4:

*   Take a 500 mL beaker filled upto ¾ with water. 

*   Dissolve 2-3 teaspoons of sugar in it.

*   Add half a spoon of yeast powder to the sugar solution.

*   Keep it covered in a warm place for 4-5 hours.

*   Now smell the solution.

*   Can you get a smell?

This is the smell of alcohol as sugar has been converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation.

Louis Pasteur discovered fermentation in 1857.

Medical use of microorganisms

Whenever you fall ill the doctor may give you some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms. These medicines kill or microorganisms. Such medicines are called antibiotics. These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline and erythromycin are some of the stop the growth of the disease-causing commonly known antibiotics which are made from fungi and bacteria. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases.

Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are also used to control many plant diseases.

It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. Also you must complete the course prescribed by the doctor. If you take antibiotics when not needed or in wrong doses, it may make the drug less effective when you might need  it in future. Also antibiotics taken unnecessarily may kill the beneficial bacteria in the body. Antibiotics, however, are not effective against cold and flu as these are caused by viruses.

In 1929, Alexander Fleming was working on a culture of disease- causing bacteria.

Suddenly he found the spores of a little green mould in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. From this the mould penicillin was prepared.

Source: This topic is taken from NCERT TEXTBOOK

VACCINE

VACCINE

When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. If dead or weakened microbes are introduced into a healthy body, the body fights and  kills the invading bacteria by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes for ever. This is how a vaccine works. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.  

In your childhood, you must have been given injections to protect yourself against several diseases. Can you prepare a list of these diseases? You may take help from your parents.

It is essential to protect all children against these diseases. Necessary vaccines are available in the nearby hospitals. You might have seen the advertisement on TV and newspapers regarding protection of children against polio under the Pulse Polio Programme. Polio drops given to children are actually a vaccine.

A worldwide campaign against smallpox has finally led to its eradication from most parts of the world.

These days vaccines are made on a large scale from microorganisms to protect humans and other animals from several diseases.

Edward Jenner discovered the vaccine for small- pox in 1798.

Source: This topic is taken from NCERT TEXTBOOK

INCREASING SOIL FERTILITY AND CLEANING THE ENVIRONMENT

INCREASING SOIL FERTILITY AND CLEANING THE ENVIRONMENT

Increasing soil fertility

Some bacteria (Fig. 2.7) are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

Figure 2.7: The Nitrogen fixing cyanobacteria (blue green algae)

Cleaning the environment

Boojho and Paheli had observed the school gardener making manure. Along with their friends, they collected wastes of plants, vegetables and fruits from nearby houses and gardens. They put them in a pit meant for waste disposal. After some time, it decomposed and got converted to manure. Boojho and Paheli wanted to know how this had happened.

Activity 2.5:

*   Take two pots and fill each pot half with soil.

*   Mark them A and B.

*   Put plant waste in pot A and things like polythene bags, empty glass bottles and broken plastic toys in pot B.

*   Put the pots aside. Observe them after 3-4 weeks.

Do you find any difference in the contents of the two pots? If so, what is the difference? You will find that plant waste in pot A, has been decomposed. How did this happen? The plant waste has been converted into manure by the action of microbes. The nutrients released in the process can be used by the plants again.

Did you notice that in pot B, the polythene bags, empty glasses, bottles and broken toy parts did not undergo any such change? The microbes could not ‘act’ on them and convert them into manure.

You often see large amounts of dead organic matter in the form of decaying plants and sometimes dead animals on the ground. You find that they disappear after some time. This is because the microorganisms decompose dead organic waste of plants and animals converting them into simple substances. These substances are again used by other plants and animals. Thus, microorganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.

Source: This topic is taken from NCERT TEXTBOOK