Solution-Class 9-Science-Chapter-8-Useful and Harmful Microbes-Maharashtra Board

Yeast reproduces asexually by the budding method.

In favourable conditions yease start growing rapidly with the process of budding, this is the asexual method of reproduction in yeast.

Toxins of fungal origin are called mycotoxins.

When fungal hyphae absorb the nutrients from the food materials, at the same time they release the mycotoxins into the food. Different species of fungi can secrete mycotoxins which is a toxic and harmful substance.

Leguminous plants can produce more proteins due to rhizobium.

Rhizobium is beneficial symbiotic bacterium that lives in the root nodules of the leguminous plants. Plants are able to produce food with high protein contents due to the process of biological nitrogen fixation by these bacteria

Plants are unable to take nitrogen from the air directly. But these bacteria convert nitrogen into compounds of nitrogen by a process of biological nitrogen fixation.

Yoghurt- Lactobacillus
Bread- Yeast
Root nodules of leguminous plants- Rhizobium
Idli- Yeast
Dosa- Yeast
Spoiled potato curry- Clostridium

i. Cholera is the odd one out because all others are diseases of respiratory system.

ii. Clostridia is the odd one out because all others are useful micro-organisms.

iii. Rubella is the odd one out because it is a human disease while rest of the three are plant diseases.

• During summer months, the surrounding temperature and humidity is favourable for the growth of bacteria and fungi,
• it helps rapid proliferation and growth of these organisms.
• The dal kept for a long time thus starts fermenting due to bacterial and fungal contamination.
• The fermentation releases carbon dioxide causing foam on the surface of such dal.

Naphthalene balls contains certain toxic chemicals which prevent the silverfish or termite from spoiling the cloth. The fungal growth is also arrested due to naphthalene. Since the clothes remain well preserved with naphthalene balls, they are kept with the clothes during their long term storage.

Fungal infections are caused by fungi which are found in soil, air, water, as well as on plants, animals, and people. The fungal diseases such as ringworm and other skin diseases spread through contact of the patients. The clothes, bed linen, combs, etc. spread the fungal spores or hyphae and this infects other healthy persons.

Measures which can prevent the transmission of fungal diseases are:

• one should maintain proper hygiene
• one should avoid sharing of personal products like hair brush
• avoid direct contact with people who have fungal infection
• clean or discard the infected objects and garments 
• wash all bed linen regularly to get rid of any fungal spores
• one should avoid wearing tight clothes, jeans and shoes
• keeping areas like feet, groins, underarms and buttocks dry and clean

There are various kinds of vaccines which are given to infants between 0-12 months. Vaccines are given to young children because their immune systems are not yet fully mature and have less resistance power to fight against diseases. They should be protected from infectious diseases. Therefore they are given following vaccinations.

(1) The BCG vaccine is given initially within first eight days after birth. it protects infants against tuberculosis infections.

(2) In third, fourth and fifth months they are given triple vaccine or DPT which has vaccines against DPT-(Diphtheria, Pertussis, Tetanus.)

(3) At the same time they are also given oral dose of polio vaccine.

(4) In ninth month babies are given combined MMR vaccine to get protection against Mumps, Measles, Rubella.

(5) School going children are given vaccines against typhoid and cholera. Sometimes vaccination for prevention of hepatitis is also done.

Vaccines are the dead or weakened microorganisms, which help the body fight against diseases.

(1) For preparing vaccines, in olden days, microbes were injected in the bodies of horses or monkeys. These laboratory animals used to make antibodies to defend these microbes. Antibodies are proteins which can act against the disease-causing germs. These antibodies were extracted from the blood of these animals and were used as vaccines.

(2) Now a days with the advent of biotechnology. The genes and the DNA of disease-causing microbes are thoroughly explored. Then based on this information, proteins which can act against such microbes are synthetically prepared in the laboratories. The safe vaccine is produced in such a way which can defend the body against infections.

(3) Some types of vaccines are prepared from the extracts of germs. These germs or microbes are deactivated and made dormant. When they are injected in the body of a person, they initiate the defending action. The body of such vaccinated person, already develops the antibodies in his or her body. When in future, this person is again attacked by similar germs the defence starts immediately and the person does not become sick.

Microorganisms have certain biochemical pathways which are needed for their survival; for example, respiration and enzyme synthesis. Antibiotics bind with the precursors needed for these pathways, and block them. In the absence of essential life processes, the microorganisms are killed. For example, penicillin kills a bacterium by blocking the cell wall formation in bacteria. Once the disease causing organism is dead, there is no more spread of the disease and the patient starts recovering.

Animals are also affected by different kinds of diseases. They also catch infections from bacteria, virus and fungi.  Therefore, they are also given antibiotics by veterinary doctor during their treatment. Usually, the diseases which affect animals and humans are different. The bacteria infecting humans are of different species than the pathogens infecting animals, hence some of the antibiotics are different. Few, however, are similar to human antibiotics.

Vaccines are dead/weakened microorganisms which provide immunity against diseases by inducing immune response of the body. Since, these microorganisms are dead/weakened, they lose their disease causing abilities and thus pose no harm. However, if these microorganisms are not stored properly and if they are in their infective stage, they can result in widespread of the disease. 

The antibiotics that are useful against a wide variety of bacteria are called broad-spectrum antibiotics. Sometimes there are visible symptoms of the disease but the pathogen causing the disease cannot be identified. In such condition, broad spectrum antibiotics are used. Broad spectrum antibiotics kill or inhibit a wide range of gram-positive and gram-negative bacteria. Some examples are ofloxacin, vancomycin, chloramphenicol, ampicillin, amoxicillin, etc.

• Conversion of carbohydrates into alcohol and carbon dioxide in absence of oxygen is called fermentation.
• The formation of curd from milk is an example of fermentation.
• The Lactobacilli converts lactose (a type of sugar found in milk) to lactic acid.
• This reduces the pH and results in separation of milk proteins from the milk and the yoghurt is formed.

An antibiotic is an organic compound produced by a micro-organism that inhibits the growth of or kills other microorganisms. Antibiotics have controlled many bacterial diseases such as tuberculosis, and typhoid and thus have created a revolution in medical field.