The Invisible Living World: Beyond Our Naked Eye: The Invisible Living World Class 8 Extra Questions and Answers include important questions from the chapter to help students understand the concepts and prepare for their exams. These questions cover important topics such as cells, microorganisms, their uses, fermentation, decomposition, food production, and soil fertility. Students can use these questions for revision and extra practice.
The Invisible Living World Class 8 Extra Questions and Answers
Short-answer questions
Q1. Who discovered microorganisms and how did his observations contribute?
Answer: Antonie van Leeuwenhoek discovered microorganisms in the 1660s. He made better lenses and saw tiny living things like bacteria and blood cells. His work opened the study of the microscopic world and he is called the Father of Microbiology.
Q2. What are microorganisms? Name any two groups.
Answer: Microorganisms are very small living beings that cannot be seen with the naked eye. Two groups are bacteria and fungi.
Q3. Give one example each of unicellular and multicellular microorganisms.
Answer:
- Unicellular: Amoeba
- Multicellular: Mould (fungus)
Q4. Where are microorganisms commonly found? Give two examples.
Answer: Microorganisms are found everywhere. Examples: soil and pond water.
Q5. What is a microorganism? Why can most not be seen with naked eye?
Answer: A microorganism is a tiny living being. Most cannot be seen with the naked eye because they are made of one or very few cells and are too small.
Q6. Name one microorganism used in curd preparation. How does it help?
Answer: Lactobacillus is used in curd preparation. It changes milk sugar (lactose) into lactic acid, which makes milk thick and sour, forming curd.
Q7. What is fermentation? Name one microorganism involved.
Answer: Fermentation is a process in which microorganisms such as yeast break down sugars and produce substances such as alcohol and carbon dioxide.
Q8. What is the role of microorganisms in decomposition?
Answer: Microorganisms like bacteria and fungi break down dead plants and animals into simple substances. This process returns nutrients to the soil and cleans the environment.
Q9. What are the three main parts of a cell?
Answer: The three main parts of a cell are cell membrane, cytoplasm, and nucleus.
Q10. Why is the cell called the basic unit of life?
Answer: A cell is the smallest building block of life. All living things are made of cells, and cells carry out all life processes. Without cells, life cannot exist.
Q11. How does the shape of a cell help it perform its function?
Answer: The shape of a cell is linked to its job. For example, nerve cells are long and branched to carry messages quickly, while muscle cells are spindle‑shaped to help in movement.
Q12. Differentiate between plant and animal cells.
Answer:
- Plant cells: Have a cell wall, chloroplasts, and large vacuoles.
- Animal cells: Do not have a cell wall or chloroplasts, and vacuoles are small or absent.
Q13. What is the function of the cell membrane?
Answer: The cell membrane surrounds the cell, separates it from other cells, and controls the entry of food and oxygen and the exit of waste.
Q14. Why do plant cells have a cell wall?
Answer: The cell wall gives strength and rigidity to plant cells. It helps plants stand firm and protects them.
Q15. What is a nucleoid? How is it different from a nucleus?
Answer: A nucleoid is the region in bacterial cells where DNA is present. It is different from a nucleus because it does not have a nuclear membrane.
Q16. How are muscle cells and nerve cells different in shape and function?
Answer:
- Muscle cells: Spindle‑shaped, thin, and flexible. They help in movement and contraction.
- Nerve cells: Long and branched. They carry messages quickly to different parts of the body.
Q17. Explain the sequence: cell → tissue → organ → organ system → organism.
Answer:
- Cells join to form tissues.
- Tissues combine to make an organ.
- Organs work together in an organ system.
- All organ systems together form a complete organism.
Q18. Why are specialised cells important in multicellular organisms?
Answer: Specialised cells do specific jobs. For example, muscle cells help in movement, nerve cells carry messages, and stomach cells make digestive juices. This division of work helps the organism survive better.
Reason-Based Questions
Q19. Why can microorganisms not usually be seen with the naked eye?
Answer: Microorganisms are very tiny and made of one or few cells. Because of their small size, they can only be seen with the help of a microscope.
Q20. Why does dough rise when yeast is added to it?
Answer: Yeast breaks down sugar in the dough and releases carbon dioxide gas. The gas forms bubbles, which make the dough rise, soft, and fluffy.
Q21. Why does curd form more quickly when milk is kept in a warm place?
Answer: Warm conditions help bacteria like Lactobacillus grow faster. They convert milk sugar into lactic acid quickly, so curd forms faster in warm milk.
Q22. Why do pickles remain preserved for a long time when salt or oil is added?
Answer: Salt and oil create conditions that make it difficult for many microorganisms to grow, helping to prevent spoilage of pickles.
Q23. Why are microorganisms important for maintaining soil fertility?
Answer: Microorganisms decompose dead plants and animals into simple nutrients. These nutrients mix with soil and make it fertile for plant growth.
Q24. Why are legumes such as peas and beans useful for improving soil fertility?
Answer: Legumes have root nodules with Rhizobium bacteria. These bacteria fix nitrogen from air into the soil, making it rich and healthy for crops.
Q25. Why is composting considered an environmentally friendly method of managing organic waste?
Answer: Composting uses microorganisms to recycle kitchen and garden waste into manure. It reduces pollution, avoids chemical fertilizers, and improves soil naturally.
Application-Based Questions
Q26. A baker adds yeast to dough before making bread. How does yeast help in making the bread soft and spongy?
Answer: Yeast grows in the dough and breaks down sugar. It releases carbon dioxide gas, which forms bubbles. These bubbles make the bread rise, soft, and spongy.
Q27. A farmer grows peas after harvesting another crop. How can this practice help maintain soil fertility?
Answer: Peas are legumes. Their roots have nodules with Rhizobium bacteria. These bacteria fix nitrogen from the air into the soil, making it fertile for the next crop.
Q28. A family throws vegetable peels and dry leaves into a compost pit. Explain how microorganisms help in this process.
Answer: Microorganisms like bacteria and fungi act on the waste. They break it down into simple nutrients. This turns the waste into manure, which makes the soil fertile.
Q29. A student leaves cooked food uncovered for several days. What role might microorganisms play in the spoilage of the food?
Answer: Microorganisms grow on the food. They release substances that change its smell, taste, and texture. This makes the food rotten and unsafe to eat.
Q30. A student observes a drop of pond water through a microscope. What types of microorganisms might be seen?
Answer: The student may see protozoa like Amoeba and Paramecium, green algae, and sometimes bacteria. These are common in pond water.
Q31. How are microorganisms useful in both food production and waste decomposition? Give one example of each.
Answer:
- In food: Lactobacillus bacteria help in making curd.
- In waste: Fungi and bacteria decompose dead plants and animals into manure.
Q32. How can knowledge about microorganisms help us in our daily lives?
Answer: It helps us use microbes in useful ways, like making food (bread, curd), producing fuel (biogas), and cleaning waste. It also helps us prevent diseases by knowing how harmful microbes spread.
Textbook Experiment-Based Questions
Q33. Describe an activity to observe microorganisms present in pond water using a microscope. What might be observed?
Answer: Take a drop of pond water on a glass slide, cover it with a coverslip, and observe under a microscope. You may observe different microorganisms such as protozoa, algae and other tiny organisms, depending on the sample.
Q34. A student prepares two samples of dough. Yeast is added to one sample but not the other. What difference would you expect after some time? Give a reason.
Answer: The dough with yeast will rise and become soft and fluffy. The dough without yeast will remain the same. This happens because yeast releases carbon dioxide gas during fermentation, which makes the dough rise.
Q35. Describe an experiment to demonstrate that yeast releases a gas during fermentation. What observation would confirm your conclusion?
Answer: Mix sugar, yeast, and warm water in a flask. Cover the mouth with a balloon. After some time, the balloon inflates. This shows yeast releases carbon dioxide gas during fermentation.
Q36. How can an activity using milk demonstrate the role of microorganisms in curd formation?
Answer: Take two bowls of milk. Keep one in a warm place and one in a cool place. Add a spoon of curd to both. After a few hours, the warm bowl turns into curd, but the cool one does not. This shows bacteria like Lactobacillus help in curd formation in warm conditions.
Q37. What precautions should students take while observing microorganisms through a microscope?
Answer:
- Handle glass slides and coverslips carefully.
- Do not touch soil or pond water samples with bare hands.
- Use stains like methylene blue or safranin safely.
- Keep the microscope clean and adjust focus slowly.
Differentiate Questions
Q38. Differentiate between unicellular and multicellular microorganisms with one example of each.
Answer:
- Unicellular microorganisms have only one cell that does all life functions. Example: Amoeba.
- Multicellular microorganisms have many cells that work together. Example: Mould (fungus).
Q39. Differentiate between useful and harmful microorganisms. Give two examples of each.
Answer:
- Useful microorganisms: Help us in food and soil fertility. Examples: Lactobacillus (curd), Rhizobium (nitrogen fixation).
- Harmful microorganisms: Cause diseases or spoil food. Examples: Bacteria causing cholera, fungi spoiling bread.
Q40. Compare the role of microorganisms in food production and decomposition.
Answer:
- In food production, microbes like yeast and Lactobacillus help make bread, curd, and idli.
- In decomposition, microbes like fungi and bacteria break down dead plants and animals into manure, cleaning the environment.
Q41. Differentiate between fermentation and decomposition.
Answer:
- Fermentation: Microorganisms break down sugar without oxygen to make alcohol or acid. Example: Yeast in bread.
- Decomposition: Microorganisms break down dead plants and animals into simple nutrients. Example: Fungi making manure.
Q42. Compare the roles of yeast and Lactobacillus in food preparation.
Answer:
- Yeast: Used in bread and cakes. It releases carbon dioxide, making dough rise and fluffy.
- Lactobacillus: Used in curd. It changes milk sugar into lactic acid, making milk thick and sour.
Case-Based Questions
Q. Case Study: A student mixes yeast with flour, water and a little sugar and keeps the dough in a warm place. After some time, the dough becomes larger and lighter.
Q43. What role does yeast play in this activity?
Answer: Yeast grows in the dough and breaks down sugar. It releases carbon dioxide gas, which makes the dough rise and become soft.
Q44. Why does the dough increase in volume?
Answer: The carbon dioxide gas forms bubbles inside the dough. These bubbles push the dough outward, so it increases in volume.
Q45. What gas is produced during the process?
Answer: The gas produced is carbon dioxide (CO₂).
Q46. Why is sugar useful in this process?
Answer: Sugar is food for yeast. Yeast uses sugar to grow and release carbon dioxide, which helps the dough rise.
Q. Case Study: A farmer grows peas and beans in his field and later adds compost made from plant and kitchen waste to the soil.
Q47. How do microorganisms associated with legumes help the farmer?
Answer: Legumes have root nodules with Rhizobium bacteria. These bacteria fix nitrogen from air into the soil, making it fertile for crops.
Q48. How does compost improve the quality of soil?
Answer: Compost adds nutrients to the soil. It makes the soil rich and helps plants grow better.
Q49. Why can this practice reduce dependence on chemical fertilizers?
Answer: Compost and Rhizobium naturally add nutrients to the soil. This reduces the need for chemical fertilizers.
Q50. How does this practice help the environment?
Answer: It recycles waste, reduces pollution, and avoids harmful effects of chemical fertilizers on soil and water.
Q. Case Study: A student observes a drop of pond water under a microscope and notices several tiny organisms moving in the water.
Q51. Why could these organisms not be seen clearly with the naked eye?
Answer: They are very small, made of one or few cells. That is why they can only be seen with a microscope.
Q52. Name two types of microorganisms that may be found in pond water.
Answer: Amoeba and Paramecium are common microorganisms in pond water.
Q53. How can microorganisms in water contribute to an ecosystem?
Answer: Microorganisms like algae release oxygen and serve as food for aquatic animals. They help keep the ecosystem balanced.
Competency-Based Questions
Q54. A student says, “All microorganisms are harmful because they cause diseases.” Do you agree? Give reasons and suitable examples.
Answer: No, this is not correct. Some microorganisms are harmful, but many are useful.
- Harmful: Bacteria causing cholera, fungi spoiling food.
- Useful: Lactobacillus makes curd, Rhizobium increases soil fertility, and yeast helps in bread making.
Q55. Explain how microorganisms can be useful to humans in food preparation, agriculture and waste management.
Answer:
- In food: Yeast makes bread soft and fluffy, Lactobacillus makes curd.
- In agriculture: Rhizobium fixes nitrogen in soil, helping crops grow.
- In waste management: Fungi and bacteria decompose waste into manure, cleaning the environment.
Q56. A village starts converting organic household waste into compost instead of burning it. Explain two ways in which microorganisms help in this process and two benefits of composting.
Answer:
Microorganisms help by:
- Breaking down vegetable peels and leaves into simple nutrients.
- Changing waste into manure that enriches soil.
Benefits of composting:
- Reduces pollution by avoiding burning.
- Improves soil fertility naturally without chemicals.
Q57. Explain how microorganisms can be both beneficial and harmful to humans. Give suitable examples.
Answer:
- Beneficial: Yeast makes bread, Lactobacillus makes curd, Rhizobium improves soil fertility.
- Harmful: Bacteria cause diseases like typhoid, fungi spoil food like bread and fruits.
Q58. A farmer wants to improve soil fertility naturally. Suggest two practices involving microorganisms and explain how they help.
Answer:
- Growing legumes like peas and beans: Their roots have Rhizobium bacteria that fix nitrogen in soil.
- Making compost: Microorganisms decompose waste into manure, which adds nutrients to soil.
HOTS Questions
Q59. Imagine that all decomposing microorganisms suddenly disappeared from Earth. What changes would occur in the environment?
Answer: If decomposers disappeared, dead plants and animals would not break down. Waste would pile up everywhere. Soil would lose nutrients, plants would not grow well, and the balance of nature would be disturbed.
Q60. If microorganisms were visible to the naked eye, how might our understanding of the environment and our daily habits change?
Answer: If we could see microorganisms, we would notice them on food, water, soil, and even in our body. People would become more careful about hygiene and food storage. We would also better understand how microbes help in cleaning waste and making food.
Q61. A student says, “Microorganisms are tiny, so they cannot have a major effect on our lives.” Use examples from food, agriculture and the environment to explain why this statement is incorrect.
Answer: This statement is wrong. Even though microorganisms are tiny, they have big effects:
- In food: Yeast makes bread fluffy, Lactobacillus makes curd.
- In agriculture: Rhizobium fixes nitrogen and improves soil fertility.
- In environment: Bacteria and fungi decompose waste and recycle nutrients.
So, microorganisms are very important for our daily life.
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