Worksheet Solutions-2: The Invisible Living World: Beyond Our Naked Eye | Science Curiosity Class 8 - New NCERT PDF Download

Multiple Choice Questions (MCQs)

Q1: Which of the following is not a use of microorganisms?

A) Making antibiotics

B) Fixing nitrogen in the soil

C) Increasing the spoilage of food

D) Producing alcohol

Ans. C) Increasing the spoilage of food

Q2: Which microorganism is used to make curd from milk?

A) Yeast

B) Lactobacillus

C) Penicillium

D) Rhizobium

Ans. B) Lactobacillus

Q3: What is the role of microorganisms in the nitrogen cycle?

A) They decompose organic matter releasing nitrogen gas into the atmosphere.

B) They convert atmospheric nitrogen into usable compounds for plants.

C) They increase the nitrogen content in the atmosphere.

D) They consume nitrogen from the soil.

Ans. B) They convert atmospheric nitrogen into usable compounds for plants.

Q4: How do friendly microorganisms benefit humans?

A) They cause diseases.

B) They help in digestion and nutrient absorption.

C) They spoil food.

D) They reduce soil fertility.

Ans. B) They help in digestion and nutrient absorption.

Fill in the Blanks

Q1: Microorganisms that are beneficial to humans and aid in digestion are called Friendly microorganisms.

Q2: The process by which yeast helps to make bread is called Fermentation.

Q3: The technique discovered by Louis Pasteur to kill harmful microbes in milk is known as Pasteurization.

Q4: Rhizobium bacteria are known for fixing nitrogen in the soil, which helps Leguminous plants.

True/False Questions

Q1: Microorganisms can only be harmful and have no beneficial uses.

Ans. False

Q2: All bacteria are harmful to humans and other living organisms.

Ans. False

Q3: Preservation by sugar involves reducing the moisture content which inhibits bacterial growth.

Ans. True

Very Short Answer Questions

Q1: What are preservatives?

Ans. Chemicals (Salts, edible oils etc.) used to check the growths of microorganisms are called preservatives.

Q2: Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen.

Q3: Give two examples of algae.

Ans. Chlamydomonas and Spirogyra

Q4: What are the harmful effects of microorganisms on plants?

Ans. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops.

Q5: How are jams and squashes preserved?

Ans. Sodium benzoate and sodium meta bisulphite are used in the jams and squashes to check their spoilage.

Q6: How can food be preserved by adding oil and vinegar?

Ans. Use of oil and vinegar prevents spoilage of food because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.