Science and Technology Class 9 Important Questions Chapter 8 Maharashtra Board

Useful and Harmful Microbes

Short Questions

1. What are microbes?

• Microbes are tiny organisms that cannot be seen with the naked eye.

2. What shape are lactobacilli bacteria?

• Lactobacilli bacteria are rod-shaped.

3. What process do lactobacilli use to turn milk into yoghurt?

• Lactobacilli use fermentation to turn milk into yoghurt.

4. What acid is produced when lactobacilli ferment milk?

• Lactic acid is produced during fermentation.

5. Why does yoghurt taste sour?

• Yoghurt tastes sour due to the lactic acid produced by lactobacilli.

6. What is one use of lactobacilli in food production?

• Lactobacilli are used to make cheese and buttermilk.

7. What type of relationship do rhizobium bacteria have with plants?

• Rhizobium bacteria have a symbiotic relationship with leguminous plants.

8. What do rhizobium bacteria provide to plants?

• Rhizobium provide nitrates, nitrites, and amino acids to plants.

9. What do leguminous plants give to rhizobium in return?

• Leguminous plants provide carbohydrates for energy to rhizobium.

10. What is rhizobial inoculation?

• Rhizobial inoculation is coating seeds with rhizobium to help plants grow better.

11. What type of organism is yeast?

• Yeast is a unicellular fungus.

12. How does yeast reproduce?

• Yeast reproduces asexually by budding.

13. What gas does yeast produce during fermentation?

• Yeast produces carbon dioxide gas during fermentation.

14. Why does bread become spongy?

• Bread becomes spongy because yeast produces carbon dioxide, which makes the dough rise.

15. What is one use of yeast in industries?

• Yeast is used to produce ethanol alcohol in sugar factories.

16. What are antibiotics?

• Antibiotics are compounds from microbes that kill or stop harmful micro-organisms.

17. Who discovered penicillin?

• Dr. Alexander Fleming discovered penicillin in 1928.

18. What are broad-spectrum antibiotics?

• Broad-spectrum antibiotics work against a wide variety of bacteria.

19. What do clostridium bacteria cause in food?

• Clostridium bacteria cause food poisoning in cooked food.

20. What are mycotoxins?

• Mycotoxins are poisonous chemicals released by fungi on food.

Long Questions

1. How do lactobacilli bacteria help in making yoghurt?

• Lactobacilli bacteria convert the sugar in milk, called lactose, into lactic acid through fermentation. This lowers the milk’s pH, causing the proteins to coagulate and turn the milk into sour-tasting yoghurt.

2. Why do doctors suggest eating yoghurt when you have a stomach problem?

• Yoghurt contains lactobacilli, which are good bacteria that kill harmful microbes like clostridium in the stomach. This helps reduce abdominal discomfort and improves digestion.

3. How do rhizobium bacteria benefit farmers growing leguminous plants?

• Rhizobium bacteria fix nitrogen from the air and supply it as nitrates to leguminous plants like beans, making them protein-rich. This reduces the need for chemical fertilizers, saving money for farmers.

4. What is the role of yeast in bread-making, and why does the dough rise?

• Yeast ferments the sugar in the dough, producing carbon dioxide gas that gets trapped and makes the dough rise. This makes the bread spongy, soft, and easy to digest after baking.

5. How is yeast used in the production of alcohol?

• Yeast ferments sugars in molasses or grape juice to produce ethanol alcohol, used in wines and spirits. For example, Saccharomyces yeast is used in sugar factories to make ethanol as a fuel.

6. What are antibiotics, and how do they help fight diseases?

• Antibiotics are substances from microbes like fungi that kill harmful bacteria causing infections. For example, penicillin fights bacteria like Streptococci, curing diseases like pneumonia.

7. Why are fungi harmful to food items like pickles and jams?

• Fungi grow on pickles and jams, releasing mycotoxins that make the food poisonous. This spoils the food, making it unsafe to eat and causing health problems.

8. How do clostridium bacteria cause food poisoning?

• Clostridium bacteria grow in cooked food under anaerobic conditions and produce toxins. Eating this food can lead to food poisoning, especially during large gatherings like feasts.

9. What precautions should be taken while using antibiotics?

• Antibiotics should only be taken with a doctor’s prescription, and the full course must be completed. They should not be used for common colds or shared with others without advice.

10. How can microbes like yeast be used for bio-remediation?

• Yeasts like Yarrowia lipolytica absorb toxins from industrial processes, such as heavy metals in palm oil production. Bacteria like Alcanivorax also clean oil spills in oceans, protecting the environment.