Science and Technology Class 9 Question Answers Chapter 8 Maharashtra Board

Useful and Harmful Microbes

1. Complete the statements using the proper option from those given below. Explain the statements.

(mycotoxins, budding, rhizobium)

a. Yeast reproduces asexually by the ……………….. method.

Answer:
The yeast cells develop small round bodies on the parent cell. These are called buds. New daughter cells develop from these buds.

b. Toxins of fungal origin are called ……………….. .

Answer:
Mycotoxins are poisonous chemicals released into the food by fungi. This makes the food poisonous.

c. Leguminous plants can produce more proteins due to ………….. .

Answer:

(i) Nitrogenous compounds are required to produce proteins.

(ii) Rhizobia produce nitrogenous compounds by fixing atmospheric nitrogen and make it available for their host plants like leguminous plants.

2. Write the names of microbes found in the following food materials.

yogurt, bread, root nodules of leguminous plants, idli, dosa, spoiled potato curry.

Answer:

3. Identify the odd word out and say why it is the odd one?

a. Pneumonia, diphtheria, chicken pox, cholera.

Answer:
Chickenpox. It is caused by a virus, whereas others are caused by bacteria.

b. Lactobacilli, rhizobia, yeast, clostridia.

Answer:
Yeast. It is a fungus, whereas the rest are bacteria.

c. Root rot, rust (tambura), rubella, mozaic.

Answer:
Rubella. It is a disease of humans, whereas the rest are diseases of plants.

4. Give scientific reasons.

a. Foam accumulates on a the surface of ‘dal’ kept for a long time in summer.

Answer:

• Dal is rich in proteins.
• During summer, bacteria attack the dal and cause fermentation resulting in the production of carbon dioxide gas.
• Therefore, foam accumulates on the surface of the ‘dal’ kept for long time in summer.

b. Why are naphthalene balls kept with clothes to be put away.

Answer:

• Naphthalene balls are balls of chemical pesticide and deodorant.
• They help to kill or repel insects such as moths, cockroaches, mice etc.
• Therefore, naphthalene balls are kept with clothes to be put away to prevent clothes from getting damaged.

5. Write down the modes of infection and the preventive measures against fungal diseases.

Answer:

Mode of infection: Contact with infected person or his/her belongings like clothes.

Preventive measure: Personal hygiene and avoid contact with infected person.

6. Match the pairs.

‘A’ group              ‘B’ group

1. Rhizobium a. Food poisoning
2. Clostridium b. Nitrogen fixation
3. Penicillium c. Bakery products
4. Yeast d. Production of antibiotics

Answer:
(1 – b),
(2 – a),
(3 – d),
(4 – c)

7. Answer the following questions.

a. Which vaccines are given to infants? Why?

Answer:

• Hepatitis A and B, DTP (Diphtheria, Tetanus, Pertussis.) Polio, MMR (Measles, Mumps, Rubella), Chicken pox, Influenza, Tetanus, BCG, Rotavirus, etc.
• Vaccines consist of dead or weakend microbes. When these are swallowed or injected, the body produces antibodies to fight them.
• These antibodies remain in the body and protect it from any future attack of the disease causing microbes.
• Therefore, vaccines are given to infants for preventing diseases.

b. How is a vaccine produced?

Answer:

• Vaccines are made using the disease causing bacteria or virus but in a form that will not harm the human beings.
• Vaccine is made from dead or weakened microbes or their toxins.
• Vaccine stimulates the immune system to produce antibodies which give life-long protection against the disease.
• There are specific vaccines for specific diseases.

c. How do antibiotics cure disease?

Answer:
Antibiotics cure diseases by destroying or preventing the growth of harmful micro-organisms.

d. Are the antibiotics given to humans and animals the same? Why?

Answer:

• Generally, antibiotics work against any harmful bacteria, whether it is attacking humans or animals.
• But some of them are better suited to humans while some are better for animals. This is due to the adverse effects they show in different species.
• Also, the dosages of antibiotics for humans and animals differ.

e. Why is it necessary to safely store the pathogens of a disease against which vaccines are to be produced?

Answer:

• Pathogens are microbes which can cause diseases in us.
• For the preparation of a vaccine, a particular pathogen is cultured and grown in a laboratory.
• If these pathogens are not safely stored, they many get modified due to environmental factors, resulting in decrease in the efficiency of the vaccine.
• Also, the live pathogens may escape and cause diseases in us.

8. Answer the following questions in brief.

a. What are ‘broad-spectrum antibiotics’?

Answer:

Broad-spectrum antibiotics are medicines that can destroy or stop the growth of a wide variety of bacteria. They are used when the specific bacteria causing an infection are unknown but symptoms of the disease are visible. Examples include ampicillin, amoxicillin, and tetracycline. These antibiotics are effective against many types of bacteria, making them useful in treating infections like pneumonia or skin infections when the exact pathogen is not identified.

b. What is fermentation?

Answer:

• Yeast uses sugar for food.
• Yeast grows and multiplies rapidly due to the carbon compounds in the sugar solution.
• In the process of obtaining nutrition, yeast cells convert the carbohydrates in the food into alcohol and carbon dioxide.
• Also, the bacteria Lactobacilli convert lactose, the sugar in milk into lactic acid.
• This process is called fermentation.

c. Define ‘Antibiotic’.

Answer:

• Carbon compounds obtained from some bacteria and fungi for destroying or preventing the growth of harmful micro -organisms are called antibiotics.
• Antibiotics, a discovery of the 20th century, have brought a revolution in the field of medicine.
• Antibiotics mainly act against bacteria. Some antibiotics can destroy protozoa.
• Some antibiotics are useful against a wide variety of bacteria they are called broad-spectrum antibiotics. Examples – Ampicillin, amoxicillin, tetracycline, etc.