GSEB Class 8 Science Solutions Chapter 2 Microorganisms Friend and Foe

Question 1. Fill in the blanks:
(a) Microorganisms can be seen with the help of a _________.
(b) Some bacteria fix _________ directly from air and enhance fertility of soil.
(c) Alcohol is produced with the help of _________.
(d) Cholera is caused by _________
Answer:
(a) microscope
(b) nitrogen
(c) yeast
(d) bacteria.
In simple words: Microorganisms are tiny living things that you can only see with a microscope. Some bacteria help the soil by adding nitrogen from the air, making the soil more fertile. Yeast is used to make alcohol, and cholera is a disease caused by bacteria.

Exam Tip: Remember specific examples of how different microorganisms interact with the environment or human processes. For fill-in-the-blanks, recall key terms related to microbiology.

Question 2. Tick (/) the correct answer:
(a) Yeast is used in the production of -
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen.
Answer: (ii) alcohol
In simple words: Yeast is a type of microorganism that helps in making alcohol through a process called fermentation.

Exam Tip: Understand the role of yeast in fermentation and its applications in various industries, especially in the production of alcoholic beverages.

(b) The following is an antibiotic -
(i) sodium bicarbonate
(ii) streptomycin
(iii) alcohol
(iv) yeast.
Answer: (ii) streptomycin
In simple words: Streptomycin is a medicine that can kill or slow down the growth of harmful bacteria.

Exam Tip: Memorize common examples of antibiotics and their primary function, which is to fight bacterial infections.

(c) Carrier of malaria-causing protozoan is -
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly.
Answer: (i) female Anopheles mosquito
In simple words: The female Anopheles mosquito carries the tiny germ that causes malaria and spreads it to people when it bites them.

Exam Tip: It is important to know the specific vectors (carriers) of major diseases, as this is a common topic in health and biology sections.

(d) The most common carrier of communicable diseases is -
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider.
Answer: (ii) housefly
In simple words: Houseflies often carry germs from dirty places to food and surfaces, making them a very common spreader of various illnesses.

Exam Tip: Understand how different insects can act as disease carriers and which ones are most significant in spreading common illnesses in households.

(e) The bread or idli dough rises because of -
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading.
Answer: (iii) growth of yeast cells
In simple words: Yeast cells in the dough grow and create gas bubbles, which make the dough expand and become fluffy.

Exam Tip: Relate the rising of dough to the biological process of fermentation carried out by yeast, where carbon dioxide gas is produced.

(f) The process of conversion of sugar into alcohol is called -
(i) nitrogen fixation
(ii) moulding
(iii) fermentation
(iv) infection
Answer: (iii) fermentation.
In simple words: Fermentation is a natural process where sugar changes into alcohol or acid with the help of tiny living things like yeast or bacteria.

Exam Tip: Define fermentation accurately and distinguish it from other biological processes like nitrogen fixation or moulding.

Question 3. Match the organisms in Column A with their action in Column B.

Exam Tip: For matching questions, carefully read both columns and try to identify direct associations first. This helps eliminate options and make the remaining matches easier.

Question 4. Can microorganisms be seen with the naked eyes? If not, how can they be seen?
Answer: Microorganisms cannot be seen with our naked eyes. They can only be seen with the help of a microscope. This special tool makes them look much bigger, allowing us to study them.
In simple words: You cannot see microorganisms without help. You need a microscope to view them because they are very tiny.

Exam Tip: Remember that the defining characteristic of microorganisms is their microscopic size, making a microscope an essential tool for their observation.

Question 5. What are the major groups of micro-organisms?
Answer: There are four main groups of microorganisms, which include:

• Bacteria
• Fungi
• Protozoa
• Algae

Exam Tip: List all four major groups of microorganisms correctly. Briefly knowing one characteristic or example of each group can also be helpful.

Question 6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer: Bacteria, such as Rhizobium, and blue-green algae can fix atmospheric nitrogen in the soil. They play a vital role in making nitrogen available for plants.
In simple words: Rhizobium bacteria and blue-green algae are special microorganisms that help put nitrogen from the air into the soil, which plants need to grow.

Exam Tip: Focus on the specific names of microorganisms involved in nitrogen fixation, as this is a key ecological process.

Question 7. Write 10 lines on the usefulness of microorganisms in our lives.
Answer: Uses of microorganisms:

• Microorganisms help in the preparation of curd, bread, and cake.
• Yeasts are used for the commercial production of wine and alcohol.
• They are used to control many plant diseases, helping crops stay healthy.
• They are also used in making vinegar.
• They work as cleaning agents and break down waste products into manure.
• They help destroy dead plant and animal bodies by decomposing them, returning nutrients to the soil.
• They increase soil fertility by fixing nitrogen from the atmosphere.
• They are used in making medicines, such as antibiotics and vaccines.
• They are used as preservatives for many food items.
• They help in various metabolic activities inside our body, supporting digestion and other functions.

Exam Tip: When listing uses, try to categorize them (e.g., food, medicine, environment) to ensure a comprehensive answer and to remember specific examples more easily.

Question 8. Write a short paragraph on the harmful effects of microorganisms.
Answer: Microorganisms can also be very harmful to us. They cause a number of diseases in humans and other animals. For example, common cold, Tuberculosis, Measles, Chicken Pox, Polio, Cholera, Typhoid, Hepatitis B, and Malaria are some prevalent human diseases caused by these tiny organisms. Anthrax is a severe disease in animals that microbes cause. Additionally, they make food items unfit for use by causing food poisoning and also spoil clothes and leather products. They can cause diseases in plants like blights in potatoes, sugarcanes, and oranges, which then reduces crop production.
In simple words: Microorganisms can be dangerous; they cause many sicknesses in people and animals like colds, TB, and malaria. They also spoil our food, clothes, leather, and even harm plants, reducing how much food we can grow.

Exam Tip: When writing about harmful effects, provide specific examples of diseases in humans, animals, and plants, and also mention their impact on food and other materials.

Question 9. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer: Antibiotics are medicines that either kill or stop the growth of harmful microorganisms, especially bacteria, in our bodies. These are very useful to us because they protect us from the negative effects of various microorganisms. Antibiotics are typically made from bacteria and fungi. Penicillin was the first antibiotic, discovered by Alexander Fleming in 1929. Nowadays, many different antibiotics are used to treat various human and animal diseases, such as Streptomycin, Tetracycline, and Erythromycin.
Precautions:
We should only take antibiotics under the advice of a qualified doctor. Antibiotics should only be taken when truly needed, as improper use can make them less effective in the future and potentially cause harm.
In simple words: Antibiotics are special medicines that kill bad germs like bacteria or stop them from growing. You should only take them when a doctor tells you to and only for as long as needed, otherwise, they might not work as well later or could be harmful.

Exam Tip: Define antibiotics clearly, mention their source, give examples, and emphasize the critical precautions regarding doctor consultation and responsible use to prevent antibiotic resistance.