NCERT Solutions for Class 8 Science Chapter 2 The Invisible Living World: Beyond Our Naked Eye

The chapter takes students into the world of things that cannot be seen clearly with the naked eye. It explains how magnifying glasses and microscopes help us observe tiny structures, how cells form the basic unit of living organisms, and how microorganisms such as bacteria, fungi, algae and protozoa affect our lives.

Students also learn about yeast, Lactobacillus, Rhizobium, decomposition, fermentation, food spoilage, nitrogen fixation and the conditions needed for microbial growth.

If you are searching for Class 8 Science Chapter 2 question answers, Class 8 Science Chapter 2 solutions, or Microorganisms: Friend and Foe Class 8 questions and answers, this page covers the current Chapter 2 while also connecting it with the older NCERT chapter terminology.

Note: The older NCERT Class 8 Science textbook used the title “Microorganisms: Friend and Foe” for Chapter 2. The current Curiosity textbook for 2026-27 uses “The Invisible Living World: Beyond Our Naked Eye.”

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Class 8 Science Chapter 2 at a Glance

Detail	Information
Class	8
Subject	Science
Chapter	2
Current Chapter Name	The Invisible Living World: Beyond Our Naked Eye
Textbook	Curiosity
Main Topics	Microscopes, cells, microorganisms, useful microbes, decomposition, fermentation, nitrogen fixation
Older Chapter Name	Microorganisms: Friend and Foe

The current chapter contains questions, activities and investigations that connect microorganisms with cells, food, farming and the environment.

NCERT Solutions for Class 8 Science Chapter 2

1. What might you see if the invisible world around you became visible?

If the invisible world became visible, we would see many tiny living organisms around us. Microorganisms may be present in soil, water, air, food and even inside living organisms.

We would also be able to observe cells and their structures more closely.

Answer: The invisible world would reveal many tiny organisms and structures that normally cannot be seen with the naked eye.

2. How would seeing this hidden world change your idea about size and living things?

It would show that living organisms can be extremely small. Some organisms consist of only one cell, yet that cell can perform all the functions needed for life.

Answer: It would help us understand that size does not determine whether something is living. Very small organisms can carry out important life processes.

3. How do tiny living organisms interact with each other?

Microorganisms interact with one another and with larger organisms in many ways. Some help break down dead matter, some live in association with plants, and others may cause disease.

Answer: Microorganisms can cooperate, compete, decompose materials, live in association with other organisms or cause infections.

Microscopes and the Invisible World

4. Why can we not see microorganisms clearly with the naked eye?

The human eye cannot distinguish objects below a certain size. Many microorganisms are much smaller than the smallest objects that our eyes can resolve.

A magnifying glass can make small objects appear larger, while a microscope provides much greater magnification.

Answer: Microorganisms are too small to be resolved clearly by the naked eye, so instruments such as microscopes are needed to observe them.

5. How does a magnifying glass help us see small objects?

A magnifying glass contains a curved lens. The lens bends light and produces a magnified image of the object.

Answer: A magnifying glass uses a lens to produce a larger image of a small object.

6. How did microscopes help scientists study the invisible world?

Microscopes use lenses to magnify objects that are too small to be seen clearly with the naked eye. Better microscopes allowed scientists to observe cells and microorganisms in greater detail.

Robert Hooke observed tiny compartments in cork and used the word cell for them. Later, Antonie van Leeuwenhoek observed microorganisms using improved lenses.

Answer: Microscopes made it possible to observe cells and microorganisms that could not be seen clearly with the naked eye.

Also Read: NCERT Solutions for Class 8 Civics Chapter 1 The Indian Constitution

Cells and Their Structure

7. What is a cell?

A cell is the basic structural and functional unit of life.

Living organisms may consist of one cell or many cells.

Answer: A cell is the basic unit from which living organisms are made.

8. What are the main structures found in a typical cell?

Important structures include:

• Cell membrane
• Cytoplasm
• Nucleus

Plant cells also have structures such as:

• Cell wall
• Chloroplasts
• Large vacuole

Bacterial cells do not have a well-defined nucleus. Their genetic material is present in a region called the nucleoid.

9. What is the function of the cell membrane?

The cell membrane surrounds the cell and controls the movement of substances into and out of the cell.

Answer: The cell membrane regulates the exchange of materials between the cell and its surroundings.

10. What is the function of the cytoplasm?

The cytoplasm is the region inside the cell where many life processes take place.

Answer: The cytoplasm provides the space where many cellular activities occur.

11. What is the function of the nucleus?

The nucleus contains genetic material and helps control the activities of the cell.

Answer: The nucleus controls important cell activities and contains genetic information.

12. Why do different cells have different shapes?

Different cells perform different functions. Their shapes and structures are therefore suited to the jobs they perform.

For example, nerve cells are long and branched, helping them transmit messages over distances.

Muscle cells have a shape suited to contraction and relaxation.

Answer: Cell shape is related to cell function.

Plant, Animal and Bacterial Cells

13. What is common to plant and animal cells?

Both plant and animal cells have structures such as:

• Cell membrane
• Cytoplasm
• Nucleus

Answer: Cell membrane, cytoplasm and nucleus are common major structures of plant and animal cells.

14. What structures are found in plant cells but not animal cells?

Plant cells have:

• Cell wall
• Chloroplasts
• A large vacuole

Answer: Cell wall and chloroplasts are important structures that distinguish typical plant cells from animal cells.

15. How is a bacterial cell different from a typical plant or animal cell?

Bacteria are simpler cells. They do not have a well-defined nucleus enclosed by a nuclear membrane.

Their genetic material lies in a region called the nucleoid.

Answer: A bacterial cell lacks a membrane-bound nucleus and has its genetic material in a nucleoid region.

Microorganisms

16. What are microorganisms?

Microorganisms are organisms that are too small to be seen clearly with the naked eye.

Examples include:

• Bacteria
• Protozoa
• Some algae
• Fungi

Viruses are microscopic and are different from cellular microorganisms because they reproduce only inside living cells.

Answer: Microorganisms are very small organisms that generally require magnification for observation.

17. Where can microorganisms be found?

Microorganisms can be found in many environments, including:

• Soil
• Water
• Air
• Food
• Plants
• Animals
• Human bodies

Some can survive in very cold or very hot environments.

Answer: Microorganisms are widely distributed in our surroundings and can live in many different environments.

Also Read: NCERT Solutions for Class 8 History Chapter 1 How, When and Where

Useful Microorganisms

18. How do microorganisms help in decomposition?

Microorganisms such as bacteria and fungi break down dead plants, animals and organic waste into simpler substances.

The resulting material can contribute to the formation of nutrient-rich manure.

Answer: Microorganisms act as decomposers and convert organic waste into simpler substances, helping recycle nutrients.

19. Why are dry leaves mixed with fruit and vegetable waste during composting?

Dry leaves provide carbon-rich material and help create suitable conditions for decomposition.

They also improve the texture and aeration of the composting material.

Answer: Mixing dry leaves with wet organic waste helps create better conditions for microorganisms to decompose the material.

20. What would happen if microorganisms did not exist?

Dead plants and animals would decompose much more slowly, and nutrients would not be recycled efficiently.

Processes such as fermentation, curd formation and some forms of waste treatment would also be affected.

Answer: Without microorganisms, decomposition and nutrient recycling would be seriously disrupted, affecting ecosystems and many useful processes.

Microorganisms in the Kitchen

21. How does Lactobacillus help in making curd?

Lactobacillus grows in milk and helps convert it into curd.

Answer: Lactobacillus helps convert milk into curd through microbial activity.

22. What is the role of yeast in making bread?

Yeast uses sugars during fermentation and produces carbon dioxide gas.

The gas gets trapped in the dough and makes it expand.

Answer: Yeast produces carbon dioxide during fermentation, which makes bread dough rise.

23. Why does dough become soft and fluffy when yeast is added?

Yeast produces carbon dioxide during its activity. The gas forms bubbles in the dough, increasing its volume.

Answer: Carbon dioxide produced by yeast makes the dough rise and become softer and more porous.

24. Why are sugar and warm water used with yeast?

Sugar provides a source of food for yeast, while suitable warmth supports yeast activity.

The yeast then produces carbon dioxide during fermentation.

Answer: Sugar provides food for yeast and warm conditions support its activity and fermentation.

Microorganisms and Food Spoilage

25. Why does food develop mould when left outside?

Microorganisms present in the environment can grow on suitable food when conditions such as temperature and moisture allow them to multiply.

Answer: Food can develop mould because microorganisms grow on it and break down its substances.

26. Why does refrigeration slow down food spoilage?

Low temperatures slow the growth and activity of many microorganisms.

Therefore, food generally remains fresh for longer in a refrigerator.

Answer: Refrigeration slows microbial growth and therefore delays spoilage.

27. Why do pickles and similar preserved foods last longer?

Preservation methods such as adding salt or oil can create conditions that prevent or slow the growth of many microorganisms.

Answer: Preservatives and storage conditions make it difficult for many microorganisms to grow.

Fermentation

28. What is fermentation?

Fermentation is a process in which microorganisms such as yeast convert certain substances, especially sugars, into other products.

Yeast fermentation can produce alcohol and carbon dioxide.

Answer: Fermentation is a microbial process that changes sugars into products such as alcohol and carbon dioxide.

29. Why does the balloon attached to the yeast-containing test tube inflate?

Yeast acts on the sugar solution and produces a gas during fermentation.

The gas collects inside the balloon and causes it to inflate.

Answer: The balloon inflates because yeast produces carbon dioxide gas during fermentation.

30. What does lime water help us identify in the yeast experiment?

Carbon dioxide turns lime water milky.

Therefore, passing the gas produced by yeast into lime water can help confirm the presence of carbon dioxide.

Answer: Lime water is used to test for carbon dioxide.

Nitrogen Fixation

31. Why do plants need nitrogen?

Plants need nitrogen to make important substances required for growth and development, including proteins.

However, plants cannot directly use atmospheric nitrogen gas in the same way they use nitrogen-containing compounds in the soil.

32. How does Rhizobium help plants?

Rhizobium bacteria live in the root nodules of leguminous plants such as peas and beans.

They help make atmospheric nitrogen available in a form that contributes to soil fertility.

Answer: Rhizobium helps in nitrogen fixation and improves the availability of nitrogen for plants.

33. Why may a farmer growing beans use less nitrogen fertiliser?

Leguminous plants such as beans have a relationship with nitrogen-fixing bacteria such as Rhizobium.

These bacteria contribute to nitrogen availability in the soil.

Answer: Rhizobium associated with leguminous plants helps in nitrogen fixation, reducing dependence on added nitrogen in some situations.

Conditions Needed for Microbial Growth

34. What conditions do microorganisms need to grow?

Different microorganisms have different requirements, but factors such as:

• Temperature
• Moisture
• Air or oxygen availability
• Food or nutrients

can affect microbial growth.

Answer: Microbial growth depends on suitable environmental conditions such as temperature, moisture, nutrients and, for many microbes, suitable air or oxygen conditions.

35. How can you test whether microorganisms need suitable temperature, air and moisture?

Set up several samples under different conditions.

For example:

• Keep one moist sample in a warm place.
• Keep another in a cold place.
• Keep another dry.
• Keep another with limited air.

Observe the growth over several days while keeping other conditions as similar as possible.

Answer: Comparing microbial growth under controlled changes in temperature, moisture and air can show how these factors affect growth.

Important NCERT Application Questions

36. A student keeps one slice of bread near a sink and another in a refrigerator. What is likely to happen?

The slice kept in a warm, moist environment is likely to show microbial growth sooner.

The refrigerated slice is likely to remain fresh for longer because low temperature slows microbial growth.

Answer: The bread near the sink is likely to spoil faster than the refrigerated bread.

37. Why does curd become more sour when left outside for a long time?

Microbial activity can continue after curd is prepared. Continued activity can increase the production of acids, making the curd taste more sour.

Answer: Continued microbial activity can increase acidity, making the curd more sour.

38. What are some useful roles of microorganisms?

Microorganisms are useful in:

• Making curd
• Making bread
• Fermentation
• Decomposition
• Composting
• Nitrogen fixation
• Biogas production
• Food processing

Answer: Microorganisms support food production, agriculture, waste decomposition and several industrial processes.

39. What are some harmful effects of microorganisms?

Some microorganisms can:

• Cause diseases
• Spoil food
• Damage crops
• Contaminate stored materials

Answer: Harmful microorganisms can cause disease and spoil food and other useful materials.

NCERT Class 8 Science Chapter 2 Notes

Microscopes

Microscopes use lenses to magnify tiny objects.

They made it possible for scientists to study cells and microorganisms that cannot be observed clearly with the naked eye.

Cells

A cell is the basic unit of life.

Important cell structures include:

Cell membrane: controls movement of substances.

Cytoplasm: where many cellular activities occur.

Nucleus: contains genetic material and controls cell activities.

Cell wall: gives plant cells strength and support.

Chloroplast: contains chlorophyll and helps plants carry out photosynthesis.

Nucleoid: region containing genetic material in bacterial cells.

Microorganisms

Important groups discussed in this context include:

• Bacteria
• Fungi
• Protozoa
• Some algae

Viruses are microscopic and reproduce only inside living host cells.

Useful Microorganisms

Lactobacillus

Helps in curd formation.

Yeast

Used in fermentation and baking.

Rhizobium

Helps with nitrogen fixation in association with leguminous plants.

Decomposing microorganisms

Break down dead organic matter and help recycle nutrients.

Class 8 Science Chapter 2 Question Answer Practice

Question 1. Why are microorganisms called microscopic organisms?

Answer: They are extremely small and generally cannot be seen clearly with the naked eye.

Question 2. Name one microorganism used in curd formation.

Answer: Lactobacillus.

Question 3. Which microorganism is commonly used in baking?

Answer: Yeast.

Question 4. Which bacterium is associated with nitrogen fixation in leguminous plants?

Answer: Rhizobium.

Question 5. What gas is produced by yeast during fermentation?

Answer: Carbon dioxide.

Question 6. What happens when carbon dioxide is passed through lime water?

Answer: Lime water turns milky.

Question 7. Why are microorganisms important decomposers?

Answer: They break down dead organic matter into simpler substances and help recycle nutrients.

Question 8. Why does refrigeration help preserve food?

Answer: Low temperature slows the growth of many microorganisms.

Question 9. What is the basic unit of life?

Answer: The cell.

Question 10. Why do cells have different shapes?

Answer: Their shapes are related to the functions they perform.

Class 8 Science Chapter 2 Extra Questions

1. Why is a microscope important in the study of microorganisms?

A microscope magnifies tiny objects and allows scientists and students to observe microorganisms and cellular structures that cannot be seen clearly with the naked eye.

2. Why is yeast useful in bread making?

Yeast ferments sugars and produces carbon dioxide. The gas gets trapped in the dough and causes it to rise.

3. Why are decomposers important for the environment?

They break down dead organic matter and return nutrients to the environment.

4. How does Rhizobium benefit leguminous plants?

Rhizobium helps fix atmospheric nitrogen in association with the roots of leguminous plants.

5. Why does food spoil faster outside a refrigerator?

Suitable temperature and moisture can allow microorganisms to grow faster, leading to quicker spoilage.

6. What is the difference between a plant cell and a bacterial cell?

A typical plant cell has a well-defined nucleus, cell wall and chloroplasts. A bacterial cell does not have a membrane-bound nucleus and instead has a nucleoid.

7. Why is carbon dioxide important in the yeast experiment?

Carbon dioxide is a product of yeast fermentation. Its production provides evidence that fermentation is taking place.

8. Why are microorganisms important in agriculture?

Some microorganisms help improve soil fertility, decompose organic matter and make nutrients available to plants.

9. What would happen if decomposition stopped?

Dead plants, animals and organic waste would accumulate, and nutrients would not be recycled efficiently.

10. Give two examples of useful microorganisms.

Lactobacillus helps in curd formation, while yeast is used in baking and fermentation.

Class 8 Science Chapter 2 Worksheet With Answers

A. Fill in the blanks

1. The basic unit of life is the ________.
2. A microscope helps us observe very ________ objects.
3. ________ is used in bread making.
4. ________ helps in curd formation.
5. ________ is associated with nitrogen fixation in leguminous plants.
6. Yeast produces ________ during fermentation.
7. The region containing genetic material in a bacterial cell is called the ________.
8. ________ helps slow microbial growth in food.

Answers

1. cell
2. small
3. yeast
4. Lactobacillus
5. Rhizobium
6. carbon dioxide
7. nucleoid
8. refrigeration

B. Multiple Choice Questions

1. Which instrument helps us observe microorganisms?

1. a) Telescope
   b) Microscope
   c) Compass
   d) Thermometer

Answer: b) Microscope

2. Which microorganism helps in curd formation?

1. a) Yeast
   b) Lactobacillus
   c) Rhizobium
   d) Amoeba

Answer: b) Lactobacillus

3. Which organism is commonly used in bread making?

1. a) Yeast
   b) Rhizobium
   c) Amoeba
   d) Algae

Answer: a) Yeast

4. Which gas is produced by yeast during fermentation?

1. a) Oxygen
   b) Nitrogen
   c) Carbon dioxide
   d) Hydrogen

Answer: c) Carbon dioxide

5. Which structure is present in plant cells but not typical animal cells?

1. a) Cell membrane
   b) Cytoplasm
   c) Cell wall
   d) Nucleus

Answer: c) Cell wall

6. What is the genetic-material region in a bacterial cell called?

1. a) Nucleus
   b) Nucleoid
   c) Chloroplast
   d) Vacuole

Answer: b) Nucleoid

Class 8 Science Chapter 2 Short Question Answers

Q1. What is a microorganism?

A microorganism is an organism that is too small to be seen clearly with the naked eye.

Q2. What is fermentation?

Fermentation is a microbial process in which substances such as sugars are converted into other products. Yeast can produce alcohol and carbon dioxide during fermentation.

Q3. What is nitrogen fixation?

Nitrogen fixation is the conversion of atmospheric nitrogen into forms that can contribute to nitrogen availability for plants.

Q4. What is decomposition?

Decomposition is the breakdown of dead organic matter into simpler substances by decomposers such as bacteria and fungi.

Q5. What is the role of chloroplasts?

Chloroplasts contain chlorophyll and are involved in photosynthesis in plant cells.

Q6. Why are nerve cells long and branched?

Their long and branched structure helps them transmit messages efficiently over distances.

Important Terms for Class 8 Science Chapter 2

Term	Meaning
Microorganism	Very small organism requiring magnification for observation
Microscope	Instrument used to magnify tiny objects
Cell	Basic unit of life
Nucleus	Cell structure containing genetic material in typical eukaryotic cells
Nucleoid	Region containing genetic material in bacteria
Fermentation	Microbial conversion of substances such as sugars
Decomposition	Breakdown of dead organic matter
Rhizobium	Nitrogen-fixing bacterium associated with leguminous plants
Lactobacillus	Bacterium involved in curd formation
Yeast	Fungus used in baking and fermentation
Chloroplast	Plant-cell structure containing chlorophyll
Pathogen	Disease-causing organism or agent

Quick Revision for Class 8 Science Chapter 2

Remember these points before your test:

• Microscopes help us observe very small objects.
• Cells are the basic units of life.
• Plant and animal cells share several structures but also have important differences.
• Bacteria do not have a membrane-bound nucleus.
• Microorganisms are found in soil, water, air, food and living bodies.
• Lactobacillus helps in curd formation.
• Yeast is useful in baking and fermentation.
• Yeast fermentation produces carbon dioxide.
• Rhizobium is associated with nitrogen fixation in leguminous plants.
• Microorganisms help decompose organic waste.
• Some microorganisms cause diseases and food spoilage.
• Refrigeration slows the growth of many microorganisms.
• Temperature, moisture, nutrients and other environmental conditions affect microbial growth.