Important Questions Class 8 Science Chapter 2: The Invisible Living World Beyond Our Naked Eye

Cells are the basic units of life that form the bodies of all living organisms.
Microorganisms are tiny living beings that usually need a microscope for observation.

The invisible living world includes cells, microorganisms, fungi, bacteria, protozoa, algae and viruses that cannot be studied fully with the naked eye. Important Questions Class 8 Science Chapter 2 help students practise cell structure, plant and animal cells, microorganisms, microscope observations, decomposition, fermentation, yeast, Lactobacillus, Rhizobium, microalgae and beneficial microbes. The CBSE 2026 chapter explains these ideas through onion peel cells, cheek cells, pond water, soil suspension, curd formation, dough rising and manure formation.

Key Takeaways

• Cell: All living organisms are made of cells, and a cell is the basic unit of life.
• Microscope: A microscope magnifies tiny living forms that cannot be seen with unaided eyes.
• Microorganisms: Bacteria, protozoa, fungi and some algae are microorganisms.
• Fermentation: Yeast and Lactobacillus help prepare foods such as bread, curd, idli and dosa.

Important Questions Class 8 Science Chapter 2 Structure 2026

Important Questions Class 8 Science Chapter 2 with Answers

The Invisible Living World: Beyond Our Naked Eye explains cells and microorganisms through microscope-based observations.
Students should connect every answer with cell structure, microscope use, microbial diversity or microbe-based processes.
These the invisible living world class 8 questions follow the NCERT 2026 chapter flow.

1. What does Important Questions Class 8 Science Chapter 2 mainly teach?

Important Questions Class 8 Science Chapter 2 mainly teach cells, microorganisms, microscopes, fermentation, decomposition and beneficial microbes. The chapter shows how invisible living forms affect life and the environment.

1. Cell Skill: Identify cell membrane, cytoplasm and nucleus.
2. Microscope Skill: Observe cells and microorganisms.
3. Microbe Skill: Classify bacteria, fungi, protozoa and algae.
4. Application Skill: Explain curd formation, dough rising and manure formation.
5. Final Result: Chapter 2 teaches the hidden living world beyond naked-eye vision.

2. What is the name of Class 8 Science Chapter 2?

The name of Class 8 Science Chapter 2 is The Invisible Living World: Beyond Our Naked Eye. It explains cells and microorganisms.

1. Chapter Number: 2.
2. Chapter Name: The Invisible Living World: Beyond Our Naked Eye.
3. Textbook: Curiosity.
4. Final Result: Chapter 2 studies cells and tiny living beings.

3. Why is this chapter called The Invisible Living World?

This chapter is called The Invisible Living World because many living beings are too small to see with naked eyes. Microscopes make them visible.

1. Invisible Forms: Bacteria and protozoa.
2. Viewing Tool: Microscope.
3. Hidden World: Pond water and soil contain microbes.
4. Final Result: Microscopes reveal tiny living organisms.

Class 8 Science Chapter 2 Important Questions

Class 8 Science Chapter 2 important questions focus on cells and microorganisms.
The chapter begins with the limits of human vision and the invention of magnifying tools.
Students should use examples such as onion peel, cheek cell, yeast and Lactobacillus.

4. Why can the human eye not see microorganisms?

The human eye cannot see microorganisms because they are below the visible size limit of unaided vision. A microscope magnifies them.

1. Unaided Eye: Sees only objects above a certain size.
2. Microorganisms: Too small to see directly.
3. Tool Needed: Microscope.
4. Final Result: Microorganisms need magnification for observation.

5. What is a lens?

A lens is a curved piece of glass that can make small objects appear larger. Early lenses were shaped like lentil seeds.

1. Shape: Thick in the middle and thin at the edge.
2. Function: Magnifies objects.
3. Use: Reading glasses and microscopes.
4. Final Result: A lens helps magnify small objects.

6. How does a water-filled round-bottom flask work like a magnifying glass?

A water-filled round-bottom flask bends light and makes letters appear larger. It acts like a simple magnifying glass.

1. Material: Glass flask and water.
2. Observation: Letters look larger.
3. Reason: Curved water-filled surface magnifies.
4. Final Result: The flask acts as a magnifier.

7. Why was the invention of the microscope important?

The microscope was important because it opened the hidden world of tiny living organisms. It helped scientists study cells and microbes.

1. Before Microscope: Tiny organisms remained unknown.
2. After Microscope: Cells and bacteria became visible.
3. Science Impact: Microbiology developed.
4. Final Result: Microscope revealed the microscopic living world.

8. Who was Robert Hooke?

Robert Hooke was a scientist who published Micrographia in 1665. He first used the word cell for tiny spaces seen in cork.

1. Book: Micrographia.
2. Year: 1665.
3. Observation: Cork had small compartments.
4. Final Result: Robert Hooke introduced the term cell in science.

9. Who was Antonie van Leeuwenhoek?

Antonie van Leeuwenhoek was a Dutch scientist who made improved lenses and microscopes. He clearly observed bacteria and blood cells.

1. Contribution: Improved microscopes.
2. Observation: Tiny living things and blood cells.
3. Title: Father of Microbiology.
4. Final Result: Leeuwenhoek is known as the Father of Microbiology.

Cell Class 8 Science Questions

Cell class 8 science questions explain the basic unit of life.
The chapter compares cells with bricks in a wall.
All plants, animals and many microorganisms are made of cells.

10. What is a cell?

A cell is the basic unit of life. All living organisms are made of one or more cells.

1. Plants: Made of cells.
2. Animals: Made of cells.
3. Microorganisms: May have one or more cells.
4. Final Result: A cell is the building block of living organisms.

11. Why is a cell called the basic unit of life?

A cell is called the basic unit of life because it performs essential life functions. Organisms survive because their cells work.

1. Structure: Forms body parts.
2. Function: Performs life processes.
3. Survival: Supports organism’s activities.
4. Final Result: Life functions occur through cells.

12. What are the three basic parts of a cell?

The three basic parts are cell membrane, cytoplasm and nucleus. These parts are seen in many typical cells.

1. Cell Membrane: Outer boundary.
2. Cytoplasm: Jelly-like internal material.
3. Nucleus: Controls cell activities.
4. Final Result: Cell membrane, cytoplasm and nucleus are basic cell parts.

13. What is the function of the cell membrane?

The cell membrane encloses the cytoplasm and nucleus. It allows useful materials to enter and waste materials to leave.

1. Boundary: Separates one cell from another.
2. Porous Nature: Allows movement of materials.
3. Protection: Encloses cell contents.
4. Final Result: Cell membrane controls entry and exit of materials.

14. What is cytoplasm?

Cytoplasm is the material between the cell membrane and nucleus. It contains cell components and substances such as carbohydrates, proteins, fats and mineral salts.

1. Location: Between membrane and nucleus.
2. Contents: Cell parts and compounds.
3. Life Processes: Mostly occur here.
4. Final Result: Cytoplasm is the site of many life processes.

15. What is the function of the nucleus?

The nucleus regulates all activities inside the cell. It also regulates growth.

1. Location: Usually central in many cells.
2. Function: Controls cell activities.
3. Growth: Regulates cell growth.
4. Final Result: Nucleus controls cell functions.

16. What is the function of the cell wall?

The cell wall provides rigidity and strength to plant cells. It is present outside the cell membrane.

1. Location: Outer covering in plant cells.
2. Function: Gives support.
3. Effect: Cells look firm and compact.
4. Final Result: Cell wall gives strength to plant cells.

Onion Peel Cell Class 8 Questions

Onion peel cell class 8 questions explain plant cell observation under a microscope.
The chapter uses safranin stain, glycerin and a coverslip to prepare the slide.
Onion peel cells look nearly rectangular and closely arranged.

17. Why is onion peel used to study plant cells?

Onion peel is used because it is thin and transparent. Its cells become clear under a microscope after staining.

1. Material: Thin inner onion peel.
2. Stain: Safranin gives colour.
3. Observation: Rectangular cells become visible.
4. Final Result: Onion peel helps observe plant cells clearly.

18. What is the role of safranin in onion peel slide preparation?

Safranin stains the onion peel cells pinkish red. This improves cell visibility under the microscope.

1. Stain: Safranin.
2. Colour: Pinkish red.
3. Purpose: Makes cells clear.
4. Final Result: Safranin increases contrast in onion peel cells.

19. Why is glycerin added to the onion peel slide?

Glycerin prevents the cells from drying and improves clarity. It helps preserve the slide temporarily.

1. Problem: Cells may dry.
2. Solution: Add glycerin.
3. Benefit: Clearer observation.
4. Final Result: Glycerin keeps the specimen moist.

20. Why is a coverslip placed carefully on the onion peel?

A coverslip is placed carefully to avoid air bubbles and folding of the peel. Clear placement improves observation.

1. Air Bubbles: Should be avoided.
2. Peel Folding: Should be avoided.
3. Result: Better microscopic view.
4. Final Result: A careful coverslip gives a clearer slide.

21. What do onion peel cells look like under a microscope?

Onion peel cells look nearly rectangular and closely arranged. They have a cell wall, cell membrane, cytoplasm and nucleus.

1. Shape: Nearly rectangular.
2. Arrangement: Closely packed.
3. Plant Feature: Cell wall present.
4. Final Result: Onion peel shows compact rectangular plant cells.

Cheek Cell Class 8 Questions

Cheek cell class 8 questions explain animal cell observation.
The chapter uses methylene blue stain to observe cells from the inner cheek lining.
Cheek cells appear polygon-shaped and do not have a cell wall.

22. Why are cheek cells used to study animal cells?

Cheek cells are easy to collect gently from the inner lining of the mouth. They show the structure of animal cells.

1. Source: Inner cheek lining.
2. Collection: Gentle scraping.
3. Observation: Animal cell parts become visible.
4. Final Result: Cheek cells help study animal cells.

23. What is the role of methylene blue in cheek cell observation?

Methylene blue stains cheek cells and increases contrast. This makes the nucleus and cell boundary easier to see.

1. Stain: Methylene blue.
2. Purpose: Improves visibility.
3. Observation: Nucleus becomes clearer.
4. Final Result: Methylene blue helps observe cheek cells clearly.

24. What is the shape of human cheek cells?

Human cheek cells are polygon-shaped. They form the inner lining of the mouth.

1. Cell Type: Animal cell.
2. Shape: Polygon-shaped.
3. Location: Inner cheek lining.
4. Final Result: Cheek cells are polygon-shaped animal cells.

25. What is the difference between onion peel cells and cheek cells?

Onion peel cells have a cell wall and appear rectangular, while cheek cells lack a cell wall and appear polygon-shaped. Both have a cell membrane, cytoplasm and nucleus.

1. Onion Peel Cell: Rectangular and has cell wall.
2. Cheek Cell: Polygon-shaped and lacks cell wall.
3. Common Parts: Cell membrane, cytoplasm and nucleus.
4. Final Result: Plant and animal cells differ in cell wall and shape.

26. Why do animal cells not have a cell wall?

Animal cells do not have a cell wall because they need flexibility. They are bounded only by a cell membrane.

1. Outer Boundary: Cell membrane.
2. Cell Wall: Absent.
3. Effect: Cells remain flexible.
4. Final Result: Animal cells lack a rigid cell wall.

Plant and Animal Cell Class 8 Questions

Plant and animal cell class 8 questions compare key structures.
Plant cells have cell wall, chloroplasts and a large vacuole.
Animal cells usually lack cell wall and chloroplasts.

27. What are the main features of a plant cell?

A plant cell has cell membrane, cytoplasm, nucleus, cell wall, vacuole and often chloroplasts. Chloroplasts contain chlorophyll.

1. Cell Wall: Gives strength.
2. Chloroplast: Helps photosynthesis.
3. Large Vacuole: Stores substances and supports shape.
4. Final Result: Plant cells have extra support and food-making structures.

28. What are the main features of an animal cell?

An animal cell has cell membrane, cytoplasm and nucleus. It usually lacks a cell wall and chloroplasts.

1. Cell Membrane: Outer boundary.
2. Cytoplasm: Contains cell components.
3. Nucleus: Controls activities.
4. Final Result: Animal cells lack cell wall and chloroplasts.

29. What are chloroplasts?

Chloroplasts are plastids that contain chlorophyll. They help green plant parts make food through photosynthesis.

1. Pigment: Chlorophyll.
2. Colour: Green.
3. Function: Photosynthesis.
4. Final Result: Chloroplasts help plants prepare food.

30. What is a vacuole?

A vacuole is an empty-looking space inside a cell. In plant cells, it stores substances, removes wastes and helps maintain cell shape.

1. Plant Cells: Usually have large vacuole.
2. Animal Cells: Vacuoles are absent or small.
3. Function: Storage and support.
4. Final Result: Vacuoles help storage and shape maintenance.

31. Why do cells have different shapes?

Cells have different shapes because their shapes help them perform specific functions. Structure and function are related.

1. Muscle Cell: Spindle-shaped for contraction.
2. Nerve Cell: Long and branched for messages.
3. Cheek Cell: Thin and flat for lining.
4. Final Result: Cell shape supports cell function.

32. How does a nerve cell’s shape help its function?

A nerve cell is long and branched, which helps it carry messages quickly to different body parts. It is also called a neuron.

1. Shape: Long.
2. Branches: Reach different areas.
3. Function: Carry messages.
4. Final Result: Neuron shape helps fast message transfer.

Levels of Organisation Class 8 Questions

Levels of organisation class 8 questions explain how cells build complex bodies.
Similar cells form tissues, tissues form organs, and organs form organ systems.
Organ systems together form a complete organism.

33. What are the levels of organisation in a living organism?

The levels are cell → tissue → organ → organ system → organism. This arrangement explains body organisation.

1. Cell: Basic unit.
2. Tissue: Group of similar cells.
3. Organ: Made of different tissues.
4. Organ System: Group of organs.
5. Final Result: Cells organise into complete organisms.

34. What is a tissue?

A tissue is a group of similar cells performing a function. Muscle tissue is made of muscle cells.

1. Cells: Similar type.
2. Function: Work together.
3. Example: Muscle tissue.
4. Final Result: Tissue is a group of similar working cells.

35. What is an organ?

An organ is a body part made of different tissues working together. The stomach is an organ.

1. Tissues: Different types.
2. Function: One major role.
3. Example: Stomach.
4. Final Result: An organ is made of tissues.

36. What is an organ system?

An organ system is a group of organs working together for a major body function. The digestive system is an organ system.

1. Organs: Mouth, stomach and intestines.
2. Function: Digestion.
3. Coordination: Organs work together.
4. Final Result: An organ system performs a major body function.

37. What is a multicellular organism?

A multicellular organism is made of many cells. Plants, animals and humans are multicellular organisms.

1. Meaning: Many-celled.
2. Examples: Plants and animals.
3. Organisation: Cells specialise and cooperate.
4. Final Result: Multicellular organisms contain many cells.

Microorganisms Class 8 Questions

Microorganisms class 8 questions explain tiny living beings around us.
They are found in water, soil, air, food and even inside the body.
Many microorganisms need a microscope for observation.

38. What are microorganisms?

Microorganisms are tiny living organisms that cannot be seen with the naked eye. They are also called microbes.

1. Size: Very small.
2. Tool: Microscope.
3. Examples: Bacteria, Amoeba and fungi.
4. Final Result: Microorganisms are microscopic living beings.

39. Where are microorganisms found?

Microorganisms are found in water, soil, air, food and inside our bodies. Some also live in extreme environments.

1. Water: Pond and stagnant water.
2. Soil: Moist soil suspension.
3. Body: Gut bacteria.
4. Final Result: Microorganisms are found almost everywhere.

40. What microorganisms can be seen in pond water?

Pond water may contain Amoeba, Paramecium and some algae. They can be observed under a microscope.

1. Amoeba: Single-celled protozoan.
2. Paramecium: Single-celled protozoan.
3. Algae: Green due to chlorophyll.
4. Final Result: Pond water contains microscopic life forms.

41. What microorganisms can be found in soil suspension?

Soil suspension may contain bacteria, fungi and algae. Some tiny organisms may move under the microscope.

1. Bacteria: Different shapes.
2. Fungi: Moulds or filaments.
3. Algae: Green microscopic forms.
4. Final Result: Soil suspension contains many microorganisms.

42. What is the difference between unicellular and multicellular microorganisms?

Unicellular microorganisms have one cell, while multicellular microorganisms have many cells. Bacteria and Amoeba are unicellular, while mould can be multicellular.

1. Unicellular: One cell.
2. Multicellular: Many cells.
3. Example: Yeast is unicellular fungus.
4. Final Result: Microorganisms may have one or many cells.

43. What are viruses?

Viruses are microscopic and acellular. They multiply only after entering a living cell.

1. Nature: Acellular.
2. Multiplication: Inside living cells.
3. Effect: May cause diseases in plants, animals or bacteria.
4. Final Result: Viruses differ from cellular microorganisms.

Bacteria Class 8 Science Questions

Bacteria class 8 science questions explain single-celled microorganisms.
Bacteria may be spherical, comma-shaped, spiral or rod-shaped.
Some bacteria are useful, while some can cause diseases.

44. What are bacteria?

Bacteria are unicellular microorganisms found in many environments. They may live in soil, water, air and the gut.

1. Cell Number: One cell.
2. Shapes: Spherical, comma, spiral or rod-shaped.
3. Location: Many environments.
4. Final Result: Bacteria are single-celled microorganisms.

45. What is a nucleoid?

A nucleoid is the region in a bacterial cell that contains genetic material. Bacteria do not have a well-defined nucleus.

1. Cell Type: Bacterial cell.
2. Nucleus: Not well-defined.
3. Region: Nucleoid.
4. Final Result: Nucleoid replaces a true nucleus in bacteria.

46. How are bacteria different from plant and animal cells?

Bacteria lack a well-defined nucleus and nuclear membrane. Plant and animal cells have a well-defined nucleus.

1. Bacteria: Have nucleoid.
2. Plant Cell: Has nucleus and cell wall.
3. Animal Cell: Has nucleus but no cell wall.
4. Final Result: Bacteria are structurally different from plant and animal cells.

47. How do gut bacteria help humans?

Gut bacteria help digestion inside the intestine. They support the digestive process.

1. Location: Human intestine.
2. Role: Help digestion.
3. Connection: Animals host useful microbes.
4. Final Result: Some bacteria help digestion in humans.

48. Why is Rhizobium useful for plants?

Rhizobium traps nitrogen from air and makes it useful for plants. It lives in root nodules of legumes.

1. Bacterium: Rhizobium.
2. Plant Group: Beans, peas and lentils.
3. Function: Adds useful nitrogen.
4. Final Result: Rhizobium improves soil fertility.

49. Why do farmers grow legumes in crop rotation?

Farmers grow legumes because their root nodules contain Rhizobium. These bacteria increase nitrogen in the soil.

1. Legumes: Beans, peas and lentils.
2. Root Nodules: Contain Rhizobium.
3. Benefit: Healthier soil for next crop.
4. Final Result: Legumes naturally enrich soil nitrogen.

Fungi Class 8 Science Questions

Fungi class 8 science questions explain microorganisms such as yeast and mould.
Some fungi are unicellular, while others are multicellular.
Fungi can help fermentation and decomposition.

50. What are fungi?

Fungi are a group of microorganisms that may be unicellular or multicellular. Yeast and mould are fungi.

1. Yeast: Unicellular fungus.
2. Mould: Multicellular fungus.
3. Food Role: Fermentation.
4. Final Result: Fungi include yeast and moulds.

51. Why do moulds grow on rotting fruits?

Moulds grow on rotting fruits because microbes are present in air and surroundings. They infect exposed food and multiply.

1. Food Item: Lemon, tomato or orange.
2. Growth: Powdery or cotton-like.
3. Cause: Microbial infection.
4. Final Result: Mould growth shows microbial activity.

52. Why do pickles and murabbas not get spoiled easily?

Pickles and murabbas do not spoil easily because high salt or sugar concentration prevents microbial growth. Spices also act as preservatives.

1. Salt: Inhibits microbes.
2. Sugar: Inhibits microbes.
3. Spices: Act as preservatives.
4. Final Result: Preservatives reduce microbial growth.

53. How do fungi help the environment?

Some fungi decompose plant and animal waste into simpler substances. This returns nutrients to the soil.

1. Waste: Leaves, peels and dead matter.
2. Process: Decomposition.
3. Result: Nutrient-rich substances.
4. Final Result: Fungi help recycle nutrients.

Yeast Fermentation Class 8 Questions

Yeast fermentation class 8 questions explain why dough rises.
Yeast respires and releases carbon dioxide in warm, sugary dough.
This gas makes the dough soft and fluffy.

54. What is yeast?

Yeast is a unicellular fungus used in food preparation. It helps make dough soft and fluffy.

1. Group: Fungi.
2. Cell Number: One cell.
3. Use: Bread and cake making.
4. Final Result: Yeast is a useful unicellular fungus.

55. Why does dough rise when yeast is added?

Dough rises because yeast releases carbon dioxide during respiration. The gas forms bubbles that make dough soft and fluffy.

1. Yeast: Uses sugar.
2. Gas Produced: Carbon dioxide.
3. Effect: Dough becomes fluffy.
4. Final Result: Carbon dioxide from yeast raises dough.

56. Why is sugar added to flour in the yeast activity?

Sugar is added because yeast uses it as food. This helps yeast grow and respire.

1. Sugar: Food for yeast.
2. Respiration: Produces carbon dioxide.
3. Dough Change: Becomes fluffy.
4. Final Result: Sugar supports yeast activity.

57. Why is warm water used with yeast?

Warm water is used because yeast grows well in warm conditions. Very cold conditions slow yeast activity.

1. Condition: Warmth.
2. Effect: Better yeast growth.
3. Result: More gas formation.
4. Final Result: Warm conditions help yeast ferment dough.

58. Why does yeast dough have a different smell?

Yeast dough smells different because yeast produces a small amount of alcohol during fermentation. Carbon dioxide is also released.

1. Microbe: Yeast.
2. Product: Small amount of alcohol.
3. Smell: Slightly different odour.
4. Final Result: Alcohol formation changes the dough smell.

Lactobacillus Class 8 Questions

Lactobacillus class 8 questions explain curd formation.
Curd contains bacteria that ferment milk.
Warm milk turns into curd faster than cold milk.

59. What is Lactobacillus?

Lactobacillus is a bacterium present in curd. It ferments milk sugar and helps form curd.

1. Microbe Type: Bacterium.
2. Food Source: Milk sugar called lactose.
3. Product: Lactic acid.
4. Final Result: Lactobacillus helps convert milk into curd.

60. How is curd formed from milk?

Curd forms when Lactobacillus feeds on lactose and produces lactic acid. This makes milk curdle and become sour.

1. Starter: Small amount of curd.
2. Milk Sugar: Lactose.
3. Product: Lactic acid.
4. Final Result: Lactic acid converts milk into curd.

61. Why is lukewarm milk better for curd formation?

Lukewarm milk is better because Lactobacillus grows well in warm conditions. Cold conditions slow curd formation.

1. Bowl A: Lukewarm milk forms curd.
2. Bowl B: Cold milk may not curdle well.
3. Reason: Bacteria grow better in warmth.
4. Final Result: Warmth supports curd-forming bacteria.

62. Why does curd become sour?

Curd becomes sour because Lactobacillus produces lactic acid. More bacterial activity increases sourness.

1. Bacterium: Lactobacillus.
2. Substrate: Lactose.
3. Product: Lactic acid.
4. Final Result: Lactic acid gives curd its sour taste.

63. Which microbes help make idli, dosa and bhatura?

Lactobacillus and some other bacteria help ferment batter for idli and dosa and dough for bhatura. Fermentation changes texture and taste.

1. Idli Batter: Fermented by bacteria.
2. Dosa Batter: Fermented by bacteria.
3. Bhatura Dough: Fermented before cooking.
4. Final Result: Bacteria help ferment common foods.

Microalgae Class 8 Questions

Microalgae class 8 questions explain tiny plant-like organisms.
They live in water, soil, air and on trees.
They produce oxygen and serve as food for aquatic animals.

64. What are microalgae?

Microalgae are microscopic plant-like organisms. They make their own food using sunlight.

1. Size: Microscopic.
2. Nature: Plant-like.
3. Food-making: Use sunlight.
4. Final Result: Microalgae are tiny photosynthetic organisms.

65. Why are microalgae important?

Microalgae are important because they release oxygen and form food for aquatic animals. They produce more than half of Earth’s oxygen supply.

1. Oxygen: Released during food-making.
2. Aquatic Food: Supports water animals.
3. Human Use: Supplements and medicines.
4. Final Result: Microalgae support oxygen balance and food chains.

66. What is Spirulina?

Spirulina is a microalga used as a health supplement. It is rich in protein and vitamin B12.

1. Type: Microalga.
2. Nutrient: More than 60% protein by body weight.
3. Use: Health supplement.
4. Final Result: Spirulina is a nutrient-rich microalga.

67. Why should microalgae be conserved?

Microalgae should be conserved because pollution, climate change and habitat destruction threaten them. They help maintain oxygen balance.

1. Threats: Pollution and habitat loss.
2. Role: Oxygen production.
3. Use: Food security and biofuel.
4. Final Result: Microalgae conservation supports ecosystems.

Decomposition Class 8 Questions

Decomposition class 8 questions explain how microbes clean the environment.
Bacteria and fungi break down dead plants, animals and waste.
This returns nutrients to soil.

68. What is decomposition?

Decomposition is the breakdown of complex waste into simpler substances by microorganisms. It returns nutrients to the soil.

1. Waste: Fallen leaves and peels.
2. Microbes: Bacteria and fungi.
3. Result: Nutrient-rich matter.
4. Final Result: Decomposition recycles nutrients.

69. How do microorganisms help make manure?

Microorganisms act on fruit and vegetable peels and break them down. The waste turns into dark nutrient-rich manure.

1. Waste: Fruit and vegetable peels.
2. Microbes: Bacteria and fungi.
3. Product: Manure.
4. Final Result: Microbes convert plant waste into manure.

70. Why do gardeners collect dry leaves and plant waste in pits?

Gardeners collect plant waste in pits to make natural manure. Microbes break the waste into nutrient-rich material.

1. Material: Dry leaves and plant waste.
2. Process: Decomposition.
3. Use: Soil fertility.
4. Final Result: Plant waste pits produce manure.

71. What conditions help manure formation?

Optimal temperature and appropriate moisture help manure formation. Microorganisms grow and act better under suitable conditions.

1. Temperature: Should be suitable.
2. Moisture: Should be appropriate.
3. Microbial Action: Breaks waste.
4. Final Result: Warm and moist conditions support decomposition.

72. What would happen if microorganisms did not exist on Earth?

Dead plants, animals and wastes would not decompose properly. Nutrients would not return to soil efficiently.

1. Waste: Would accumulate.
2. Nutrient Recycling: Would reduce.
3. Soil Fertility: Would suffer.
4. Final Result: Microorganisms keep nutrient cycles active.

Beneficial Microorganisms Class 8 Questions

Beneficial microorganisms class 8 questions explain useful roles of microbes.
Microbes help in food preparation, soil fertility, digestion, biogas and environmental cleaning.
The chapter focuses on useful microbes before disease-causing microbes.

73. Give examples of beneficial microorganisms.

Yeast, Lactobacillus, Rhizobium, decomposing bacteria and microalgae are beneficial microorganisms. They help food, soil and environment.

1. Yeast: Makes dough rise.
2. Lactobacillus: Forms curd.
3. Rhizobium: Adds nitrogen to soil.
4. Final Result: Many microorganisms help humans and nature.

74. How do microbes help clean the environment?

Microbes clean the environment by decomposing plant and animal waste. They break complex substances into simpler nutrients.

1. Waste: Dead matter and peels.
2. Microbes: Bacteria and fungi.
3. Outcome: Cleaner surroundings and fertile soil.
4. Final Result: Microbes act as natural cleaners.

75. How are microbes used in biogas production?

Some microbes decompose plant and animal waste in oxygen-free conditions. They release biogas containing carbon dioxide and methane.

1. Condition: Oxygen-free environment.
2. Waste: Plant and animal waste.
3. Gas: Biogas with methane.
4. Final Result: Microbes help produce useful biogas.

76. Who was Ananda Mohan Chakrabarty?

Ananda Mohan Chakrabarty was a scientist who developed a bacterium that could break down oil spills. His discovery received a patent in 1980.

1. Field: Bacteria research.
2. Year: 1971 development.
3. Use: Oil spill cleanup.
4. Final Result: His work showed environmental use of microbes.

77. Why can microorganisms be both useful and harmful?

Microorganisms can be useful in food, soil and environment, but some can cause diseases. Their effect depends on the type and situation.

1. Useful Role: Fermentation and decomposition.
2. Useful Role: Nitrogen enrichment.
3. Harmful Role: Some microbes cause diseases.
4. Final Result: Microbes can benefit or harm living beings.

NCERT Class 8 Science Chapter 2 Questions

NCERT Class 8 Science Chapter 2 questions test cell parts, microbes, yeast, Rhizobium and decomposition.
Students should answer with named microbes and exact functions.
These NCERT Class 8 Science Chapter 2 questions follow the 2026 exercise pattern.

78. What will happen when yeast is added to warm sugar solution?

Yeast will produce carbon dioxide gas. The gas can inflate a balloon attached to the test tube.

1. Solution: Sugar and warm water.
2. Microbe: Yeast.
3. Gas: Carbon dioxide.
4. Final Result: Yeast produces gas during fermentation.

79. Why does the balloon inflate in the yeast experiment?

The balloon inflates because yeast produces carbon dioxide gas. The gas collects inside the balloon.

1. Yeast: Respire using sugar.
2. Product: Carbon dioxide.
3. Observation: Balloon expands.
4. Final Result: Carbon dioxide inflates the balloon.

80. What does lime water test show in the yeast experiment?

The lime water test shows that the gas produced by yeast is carbon dioxide. Carbon dioxide turns lime water milky.

1. Gas: From yeast activity.
2. Test Liquid: Lime water.
3. Observation: Lime water turns milky.
4. Final Result: Yeast releases carbon dioxide.

81. Why may a farmer growing beans avoid nitrogen fertiliser?

A farmer growing beans may avoid nitrogen fertiliser because bean root nodules contain Rhizobium. These bacteria make nitrogen useful for the plant.

1. Crop: Bean.
2. Root Nodules: Contain Rhizobium.
3. Benefit: Nitrogen enrichment.
4. Final Result: Rhizobium reduces need for nitrogen fertiliser.

82. What is Snehal testing with two compost pits?

Snehal is testing how mixing dry leaves with fruit and vegetable peels affects decomposition. She compares waste breakdown in two pits.

1. Pit A: Peels plus dry leaves.
2. Pit B: Peels without dry leaves.
3. Observation: Difference after 3 weeks.
4. Final Result: The test compares decomposition conditions.

83. Identify the microbe that lives in every environment and inside the gut.

The microbe is bacteria. Bacteria occur in many environments and inside the human gut.

1. Environment: Soil, water and air.
2. Body Location: Gut.
3. Role: Some help digestion.
4. Final Result: Bacteria live widely and also inside the gut.

84. Identify the microbe that makes bread and cakes soft and fluffy.

The microbe is yeast. It releases carbon dioxide, which makes dough rise.

1. Microbe: Yeast.
2. Food: Bread and cakes.
3. Gas: Carbon dioxide.
4. Final Result: Yeast makes dough soft and fluffy.

85. Identify the microbe that lives in roots of pulse crops.

The microbe is Rhizobium. It lives in root nodules and helps plants use nitrogen.

1. Crop Group: Pulses and legumes.
2. Location: Root nodules.
3. Function: Nitrogen fixation.
4. Final Result: Rhizobium supports pulse crop growth.

Class 8 Science Chapter 2 Questions and Answers

Class 8 Science Chapter 2 questions and answers should connect observations with named microbes.
Students should mention microscope use whenever cells or microbes are observed.
These answers support quick revision for school tests.

86. Why does bread mould grow faster near a sink than in a refrigerator?

Bread mould grows faster near a sink because moisture and suitable temperature support microbial growth. Refrigerator conditions slow microbial growth.

1. Near Sink: Moist and warmer.
2. Refrigerator: Cold condition.
3. Microbe: Fungi or mould.
4. Final Result: Mould grows better in warm and moist conditions.

87. Why does curd become more sour when left out for a day?

Curd becomes more sour because Lactobacillus keeps producing lactic acid. Warm conditions increase bacterial activity.

1. Microbe: Lactobacillus.
2. Product: Lactic acid.
3. Effect: More sour taste.
4. Final Result: More lactic acid makes curd sourer.

88. What happens in flask A containing warm sugar solution and yeast?

Yeast ferments sugar and produces carbon dioxide. The sugar solution changes due to yeast activity.

1. Reactants: Sugar and yeast.
2. Condition: Warmth.
3. Product: Carbon dioxide gas.
4. Final Result: Yeast ferments sugar in flask A.

89. What happens in test tube B containing lime water after yeast gas enters it?

Lime water turns milky because carbon dioxide enters it. The gas comes from yeast fermentation.

1. Gas: Carbon dioxide.
2. Liquid: Lime water.
3. Observation: Milky colour.
4. Final Result: Carbon dioxide turns lime water milky.

90. What would happen if yeast was not added to flask A?

Carbon dioxide would not form in significant amount. Lime water would not turn milky due to yeast activity.

1. No Yeast: No fermentation.
2. No Gas: Carbon dioxide not produced by yeast.
3. Observation: Balloon or lime water change absent.
4. Final Result: Yeast is required for fermentation in this setup.

91. Why is cell considered the basic unit of life?

The cell is considered the basic unit of life because every living organism is made of cells. A cell can perform essential life functions.

1. Living Bodies: Made of cells.
2. Unicellular Organisms: One cell performs all functions.
3. Multicellular Organisms: Cells specialise and cooperate.
4. Final Result: Cells form and run living organisms.

Class 8 Science Chapter List