BASIC SCIENCE FOR CLASS 8 AMARNATH MISHRA,PHD GEETA MEHTA ,PHD DEEPTI LEHRI,PHD RAJESH MOHAN, PHD

                       Biology 

                     Chapter- 3

                 Microorganisms 

A. Answer the following in not more than 20 words.

1. What is the study of microorganisms called?

   - Microbiology.

2. How do some microorganisms survive unfavorable conditions?

   - By forming spores or cysts.

3. What does the Sargasso Sea owe its name to?

   - Floating Sargassum seaweed.

4. Bacteria are divided into four groups on the basis of their shape. Name these.

   - Cocci, Bacilli, Spirilla, and Vibrios.

5. What is the major difference between a bacterial cell and the cells of other organisms?

   - Bacterial cells lack a nucleus and membrane-bound organelles.

6. How do bacteria reproduce?

   - By binary fission.

7. Mention two ways in which bacteria are helpful to us.

   - Nitrogen fixation and decomposition.

8. Do red and brown algae have chlorophyll?

   - Yes.

9. Name a protozoan which can photosynthesize.

   - Euglena.

10. Name a disease caused by a protozoan.

   - Malaria.

B. Answer the following in not more than 40 words.

1. What are diatoms? How are they useful to us?

   - Diatoms are a type of algae with silica cell walls. They are used in water filtration and as a source of biofuels.

2. Mention three uses of algae.

   - Algae are used in food products, biofuels, and pharmaceuticals.

3. How does Paramoecium move and feed?

   - Paramoecium moves using cilia and feeds by sweeping food particles into its oral groove.

4. How are protozoans in the bodies of termites and the bacteria in our intestines helpful?

   - Protozoans help termites digest cellulose, while gut bacteria aid in digestion and nutrient absorption.

5. Mention two ways in which fungi harm us.

   - Fungi can cause infections and spoil food.

C. Answer the following in not more than 100 words.

1. Explain how the growth of algae harms water bodies.

   - Excessive algae growth, or algal blooms, depletes oxygen in water, leading to dead zones where aquatic life cannot survive. This process, called eutrophication, is often caused by nutrient pollution from fertilizers and sewage.

2. Many fungi are of great use to us. Mention three ways in which we use fungi.

   - Fungi are used in the production of antibiotics (like penicillin), in fermentation processes (such as brewing and baking), and as food sources (e.g., mushrooms).

3. Why is a virus thought of as something in between the living and nonliving? How do viruses multiply within a host cell?

   - Viruses are considered between living and nonliving because they cannot reproduce or carry out metabolic processes outside a host cell. Within a host cell, they hijack the cell's machinery to replicate their genetic material and produce new virus particles.

D. Complete the following.

1. The tangled mass of threadlike structures formed by molds is called

   - Mycelium.

2. Blue-green algae are now called

   - Cyanobacteria because they are more like bacteria.

3. ______ form the link in the food chain between algae and small aquatic organisms.

   - Zooplankton.

4. ______ means the first animal.

   - Protozoa.

5. Sugar Fermentation produces carbon dioxide + 

   - Alcohol.

6. The spore case of molds is called

   - Sporangium.

E. Choose the correct option in each of the following.

1. Penicillin is obtained from a

   - (c) mould

2. Lower plants and plantlike organisms reproduce by producing a single cell encased in a tough membrane. This is called

   - (a) spore

3. Algin is derived from

   - (b) algae

4. Seabeds have large deposits of silica derived from

   - (d) diatoms

5. Microorganisms living in the roots of peas, grams, and so on, can convert nitrogen of the air to nitrates. These are

   - (a) bacteria