---
title: "NCERT Solutions Class 8 Science The Invisible Living World: Beyond Our Naked Eye"
url: https://www.swavid.com/science/class/8/chapter/the-invisible-living-world-beyond-our-naked-eye/ncert-solutions
dateModified: 2026-10-07T16:11:54+00:00
---

# NCERT Solutions Class 8 Science The Invisible Living World: Beyond Our Naked Eye

This chapter explores the microscopic world, focusing on cell structure, levels of biological organization, and the diverse roles of microorganisms in our daily lives and the environment. The questions provided encourage students to investigate, observe, and apply their understanding of these concepts through practical activities and critical thinking.

Free PDF (11 pages): https://www.swavid.com/api/seo/pdf/ncert/science/class-8/swavid-ncert-solutions-class-8-science-chapter-2-the-invisible-living-world-beyond-our-naked-eye-6298d13c7c.pdf

## Probe and ponder

### Question 1

*3 marks · Short answer*

Have you ever wondered what you might see if the invisible world around you became visible?

**Solution**

1. If the invisible world around us became visible, we would see millions of microorganisms like bacteria, protozoa, fungi, and algae existing everywhere.
2. We would observe them in water, soil, the air we breathe, and even inside the bodies of plants and animals.
3. We would also be able to see the complex cellular structures that make up all living organisms.

**Answer:** We would see a vast, hidden world of microorganisms and tiny cellular structures inhabiting every part of our surroundings.

> Common mistake: Writing about macroscopic objects instead of microscopic organisms.

### Question 2

*3 marks · Short answer*

How do you think your observation of this hidden world might change the way you think about size, complexity, or even what counts as ‘living’?

**Solution**

1. Observing the hidden microscopic world shows us that life exists at scales far smaller than what the naked eye can see.
2. It reveals incredible complexity within single-celled organisms, showing they carry out all life processes independently.
3. It broadens our definition of living beings to include unicellular organisms like bacteria and Amoeba, which are made up of just one cell.

**Answer:** It changes our perception by revealing that even microscopic single-celled entities possess remarkable complexity and are fully alive.

> Common mistake: Ignoring how single cells can perform all life processes.

### Question 3

*3 marks · Short answer*

Have you thought how these tiny living beings interact with each other?

**Solution**

1. Tiny living beings interact with each other and their environment in various beneficial and complex ways.
2. Some microorganisms like bacteria and fungi act as decomposers, breaking down plant and animal waste to enrich the soil with nutrients.
3. Others, such as Rhizobium bacteria in the root nodules of legumes, interact with plants by trapping atmospheric nitrogen to help them grow.

**Answer:** Tiny living beings interact by decomposing waste to recycle nutrients and forming symbiotic relationships like nitrogen fixation in plants.

> Common mistake: Confining interactions only to disease-causing microbes.

### Question 4

*3 marks · Short answer*

Share your questions

**Solution**

1. How do single-celled microorganisms perform all their life functions without specialized organs?
2. Why do some microorganisms cause diseases while others are helpful to humans and the environment?
3. How do microorganisms survive in extreme environments like hot springs and ice-cold regions?

**Answer:** Questions regarding how unicellular organisms survive, their dual roles as beneficial and harmful agents, and their survival in extreme habitats.

> Common mistake: Asking vague questions not related to the chapter concepts.

## Activity 2.1: Let us observe

### Question 1

*Activity*

Do you notice something interesting? The letters appear larger when seen through the flask! This happens because the flask filled with water acts like a magnifying glass. Now, use a real magnifying glass to look at small organisms, like an ant. Were you able to see the details of its body more clearly?

**Solution**

1. The round-bottom flask filled with water acts like a magnifying glass, causing the letters on the book to appear larger.
2. Using a real magnifying glass to observe small organisms like an ant makes the details of its body more clearly visible by magnifying its size.

**Answer:** Yes, a water-filled flask and a magnifying glass make small objects and the details of an ant's body appear larger and clearer.

## Activity 2.2: Let us study a cell (Teacher demonstration activity)

### Question 1

*2 marks · Very short answer*

What similarities do you find in Fig. 2.3c and Fig. 2.3d?

**Solution**

1. Both Fig. 2.3c and Fig. 2.3d show nearly rectangular structures that are closely arranged without any space between them.
2. Just like individual bricks make up a wall, individual cells make up the onion peel.

**Answer:** Both show nearly rectangular units closely arranged together without any space, similar to bricks in a wall.

> Common mistake: Writing that animals are made of bricks instead of cells.

### Question 2

*2 marks · Very short answer*

What do you think the body of an animal is made of?

**Solution**

1. All living organisms, including plants and animals, are made up of microscopic units called cells.
2. Therefore, the body of an animal is made of animal cells.

**Answer:** The body of an animal is made up of cells.

> Common mistake: Stating that animals are made of plant cells or brick-like structures.

## Activity 2.3: Let us investigate

### Question 1

*2 marks · Very short answer*

What did you observe? You will observe a polygon-shaped structure as shown in Fig. 2.4. These are cheek cells, which form the inner lining of your mouth.

**Solution**

1. When the scraped inner lining of the mouth is stained with methylene blue and observed under a microscope, we observe polygon-shaped structures.
2. These structures are human cheek cells that form the inner protective lining of the mouth.

**Answer:** We observe polygon-shaped human cheek cells that form the inner lining of the mouth.

> Common mistake: Confusing cheek cells with rectangular plant cells.

### Question 2

*3 marks · Short answer*

What similarities and differences did you observe between the cells of onion peel in Activity 2.2 and human cheek cells in Activity 2.3?

**Solution**

1. Similarities: Both onion peel cells and human cheek cells have a cell membrane, cytoplasm, and a distinct nucleus.
2. Differences in shape: Onion peel cells are nearly rectangular and closely arranged, whereas human cheek cells are polygon-shaped and thin and flat.
3. Differences in covering: Onion peel cells have an extra outer layer called a cell wall, which is absent in human cheek cells.

**Answer:** Both cell types share a cell membrane, cytoplasm, and nucleus, but onion peel cells are rectangular with a cell wall, whereas human cheek cells are polygon-shaped without a cell wall.

> Common mistake: Forgetting to mention the presence of the cell wall as a major difference between plant and animal cells.

### Question 3

*3 marks · Short answer*

What is the importance of these structures in a cell? What functions do they perform? Are these functions important for the maintenance of life?

**Solution**

1. The cell membrane encloses the contents of the cell, separates one cell from another, and allows essential materials to enter and waste to exit.
2. The cytoplasm contains various components and compounds where most of the life processes take place.
3. The nucleus regulates all activities within the cell and controls growth, making these structures vital for the maintenance of life.

**Answer:** Cell structures like the cell membrane, cytoplasm, and nucleus regulate life processes, control cell activities, and manage the exchange of materials essential for the maintenance of life.

> Common mistake: Writing general functions without linking them to specific cell parts like the membrane, cytoplasm, or nucleus.

## 2.1.1 Variation in shape and structure of cells

### Question 1

*3 marks · Short answer*

What are the similarities and differences you see in them?

**Solution**

1. Similarities: Both are types of human cells that have a cell membrane, cytoplasm, and a nucleus.
2. Differences: A muscle cell is shaped like a spindle and is flexible to help in contraction and relaxation.
3. A nerve cell (neuron) is very long and has branches to help it reach different parts of the body and pass on messages quickly.

**Answer:** Muscle cells are spindle-shaped and flexible for movement, whereas nerve cells are long and branched to transmit messages quickly.

> Common mistake: Confusing the shape of muscle cells with nerve cells.

### Question 2

*3 marks · Short answer*

Why do cells look so different from each other? Does the shape and structure of a cell relate to its function?

**Solution**

1. Cells look different from each other because their unique shape, size, and structure help them carry out specific functions in the body.
2. Yes, the shape and structure of a cell are directly related to its function.
3. For example, the long and branched structure of a nerve cell helps it transmit messages quickly, while thin and flat inner cheek cells form a protective lining.

**Answer:** Cells look different because their shape and structure are related to the specific functions they perform.

> Common mistake: Writing that all cells have the same shape and size.

## Activity 2.8: Let us perform

### Question 1

*3 marks · Short answer*

Did you find any change in the volume, smell, or texture of the dough? If not, leave the dough for some more time. After some time, you may notice that the dough in bowl A, where yeast was added, has risen slightly, become fluffy, and has a different smell compared to the dough kneaded without yeast. Why does this happen? What is the role of yeast? Why did we add sugar and warm water to the flour?

**Solution**

1. Yeast respires and breaks down sugar to release energy and carbon dioxide gas.
2. The released carbon dioxide forms bubbles inside the dough, making it soft, fluffy, and increasing its volume.
3. Warm water and sugar are added to provide the warmth and food needed for the rapid growth and respiration of yeast.

**Answer:** Yeast respires to release carbon dioxide gas, which makes the dough soft and fluffy, while warm water and sugar provide optimal conditions and food for yeast growth.

> Common mistake: Forgetting that yeast is a living organism that needs warmth and sugar for respiration.

## Keep the curiosity alive

### Question 1

*3 marks · Short answer*

Various parts of a cell are given below. Write them in the appropriate places in the following diagram: Nucleus, Cytoplasm, Chloroplast, Cell wall, Cell membrane, Nucleoid.

**Solution**

1. Common to all three cells: Cell membrane, Cytoplasm, Nucleus.
2. Only in Animal Cell: No unique category listed in the textbook diagram besides the common parts and small/absent vacuoles.
3. Only in Plant Cell: Chloroplast and Cell wall.
4. Only in Bacterial Cell: Nucleoid.

**Answer:** Common parts: Cell membrane, Cytoplasm, Nucleus; Plant cell: Chloroplast, Cell wall; Bacterial cell: Nucleoid.

> Common mistake: Confusing plant-specific structures like chloroplasts and cell walls with animal or bacterial cells.

### Question 2

*1 mark · MCQ*

(i) What do you predict will happen after 3–4 hours? She observed that the balloon attached to test tube B was inflated. What can be a possible explanation for this?

- Water evaporated in test tube B and filled the balloon with the water vapour.
- The warm atmosphere expanded the air inside the test tube B, which inflated the balloon.
- Yeast produced a gas inside the test tube B which inflated the balloon.
- Sugar reacted with warm air, which produced gas, eventually inflating the balloon.

**Solution**

1. Yeast respires and breaks down sugar to release carbon dioxide gas, which inflates the balloon.
2. Option (a), (b), and (d) are incorrect because the primary cause of inflation in test tube B is biological activity of yeast producing gas.

**Answer:** (c) Yeast produced a gas inside the test tube B which inflated the balloon.

> Common mistake: Assuming heat or water evaporation alone inflated the balloon without considering yeast respiration.

### Question 2

*3 marks · Short answer*

(ii) She took another test tube, 1/4 filled with lime water. She removed the balloon from test tube B in such a manner that the gas inside the balloon did not escape. She attached the balloon to the test tube with lime water and shook it well. What do you think she wants to find out?

**Solution**

1. Lime water is used to test for the presence of carbon dioxide gas.
2. When carbon dioxide produced by yeast mixes with lime water, it turns milky.
3. She wants to confirm that the gas produced inside the balloon during yeast fermentation is carbon dioxide.

**Answer:** She wants to confirm that the gas produced by yeast is carbon dioxide, which turns lime water milky.

> Common mistake: Forgetting that lime water turns milky in the presence of carbon dioxide.

### Question 3

*3 marks · Short answer*

A farmer was planting wheat crops in his field. He added nitrogen-rich fertiliser to the soil to get a good yield of crops. In the neighbouring field, another farmer was growing bean crops, but she preferred not to add nitrogen fertiliser to get healthy crops. Can you think of the reasons?

**Solution**

1. Wheat is a cereal crop and requires additional nitrogen-rich fertilisers for good growth.
2. Bean is a legume crop whose roots contain Rhizobium bacteria in root nodules.
3. These bacteria trap nitrogen from the air and enrich the soil naturally, so bean crops do not need added nitrogen fertilisers.

**Answer:** Beans are legumes that host Rhizobium bacteria in their root nodules, which naturally fix atmospheric nitrogen into the soil.

> Common mistake: Failing to recognize that legumes have symbiotic bacteria for nitrogen fixation.

### Question 4

*3 marks · Short answer*

Snehal dug two pits, A and B, in her garden. In pit A, she put fruit and vegetable peels and mixed it with dried leaves. In pit B, she dumped the same kind of waste without mixing it with dried leaves. She covered both the pits with soil and observed after 3 weeks. What is she trying to test?

**Solution**

1. Snehal put fruit and vegetable peels (nitrogen-rich waste) with and without dried leaves (carbon-rich waste).
2. Microorganisms decompose organic waste efficiently when there is a proper balance of carbon and nitrogen materials.
3. She is trying to test the effect of mixing carbon-rich dry leaves with nitrogen-rich kitchen waste on the rate of decomposition and manure formation.

**Answer:** She is trying to test how mixing carbon-rich dry leaves with nitrogen-rich vegetable peels affects the rate of decomposition and manure formation.

> Common mistake: Thinking that pit B will decompose faster without dry leaves.

### Question 5

*3 marks · Short answer*

Identify the following microorganisms: (i) I live in every kind of environment, and inside your gut. (ii) I make bread and cakes soft and fluffy. (iii) I live in the roots of pulse crops and provide nutrients for their growth.

**Part (i)**

1. This microorganism can survive in all kinds of environments and is found inside the human gut.

Answer (i): Bacteria

**Part (ii)**

1. This microorganism respires and releases carbon dioxide gas, making bread and cakes soft and fluffy.

Answer (ii): Yeast

**Part (iii)**

1. This microorganism lives in the root nodules of pulse and legume crops to fix atmospheric nitrogen.

Answer (iii): Rhizobium

**Answer:** (i) Bacteria, (ii) Yeast, (iii) Rhizobium

> Common mistake: Confusing yeast with bacteria or mixing up the roles of Rhizobium and Lactobacillus.

### Question 6

*3 marks · Short answer*

Design an experiment to test that microorganisms need optimal temperature, air, and moisture for their growth.

**Solution**

1. Aim: To test that microorganisms need optimal temperature, air, and moisture for growth.
2. Method: Take three identical containers with moist bread slices. Keep container 1 in a warm place with air, container 2 in a refrigerator (low temperature), and container 3 inside an airtight sealed bag with no fresh air.
3. Observation: Bread in container 1 shows maximum fungal growth (mould), while containers 2 and 3 show little to no growth.
4. Conclusion: Microorganisms require optimal temperature, moisture, and air for their growth.

**Answer:** Microorganisms need optimal temperature, air, and moisture for growth.

> Common mistake: Forgetting to mention all three conditions (temperature, air, and moisture) in the experimental design.

### Question 7

*3 marks · Short answer*

Take 2 slices of bread. Place one slice in a plate near the sink. Place the other slice in the refrigerator. Compare after three days. Note your observations. Give reasons for your observations.

**Solution**

1. Given: Two slices of bread placed near the sink and in the refrigerator respectively.
2. Observation: After three days, the slice near the sink shows powdery or cotton-like fungal growth (mould), whereas the slice in the refrigerator shows no visible growth.
3. Reason: Microorganisms like fungi grow well in warm and moist conditions. The refrigerator has a low temperature which prevents microbes from growing and spoiling the bread.

**Answer:** The slice near the sink grows mould due to warmth and moisture, while the refrigerator's low temperature prevents microbial growth.

> Common mistake: Not explaining the role of temperature in slowing down or stopping microbial activity.

### Question 8

*3 marks · Short answer*

A student observes that when curd is left out for a day, it becomes more sour. What can be two possible explanations for this observation?

**Solution**

1. Given: Curd left out for a day becomes more sour.
2. Explanation 1: The Lactobacillus bacteria present in the curd continue to feed on the lactose sugar and multiply, producing more lactic acid over time.
3. Explanation 2: Keeping curd out exposes it to warmer room temperatures, which speeds up bacterial activity and acid production.

**Answer:** Continued multiplication of lactic acid bacteria and warmer temperature lead to higher acid production and increased sourness.

> Common mistake: Confusing lactic acid production by bacteria with alcoholic fermentation by yeast.

### Question 9

*4 marks · Case-based*

Observe the set-up given in Fig. 2.15 and answer the following questions. (i) What happens to the sugar solution in flask A? (ii) What do you observe in test tube B after four hours? Why do you think this happened? (iii) What would happen if yeast was not added in flask A?

**Part (i)**

1. Yeast respires and breaks down the sugar in the warm solution.
2. During this process, bubbles of carbon dioxide gas are released into flask A.

Answer (i): The sugar solution undergoes fermentation by yeast, releasing bubbles of carbon dioxide gas.

**Part (ii)**

1. The lime water in test tube B turns milky.
2. This happens because carbon dioxide gas released from flask A travels into test tube B and reacts with lime water.

Answer (ii): Lime water turns milky due to the passage of carbon dioxide gas produced during yeast respiration.

**Part (iii)**

1. Without yeast, no fermentation of the sugar solution would take place.
2. No carbon dioxide gas would be produced, and the lime water in test tube B would remain unchanged.

Answer (iii): No fermentation would occur, and lime water would not turn milky.

**Answer:** Yeast respires in warm sugar solution, releasing carbon dioxide gas which turns lime water milky.

> Common mistake: Assuming oxygen is released instead of carbon dioxide during yeast respiration.

## Frequently asked questions

### How many total questions are covered in the NCERT solutions for Class 8 Science Chapter 2?

The solutions cover a total of 24 questions across various sections, including probe and ponder, activities, and the keep the curiosity alive exercises. SwaVid's free PDF and step-by-step solutions are available on this page only to help you practice all of them easily.

### Which topics are covered in the questions for this chapter?

The questions cover important topics such as microorganisms, cell structure, onion peel and human cheek cells, variation in cell shapes, and yeast fermentation. You can find detailed answers for all these concepts in the free PDF provided on this page.

### Are there case study and multiple-choice questions in this chapter's solutions?

Yes, the keep the curiosity alive section includes case-based and multiple-choice questions alongside short answer questions. These tougher questions test your understanding of microbial growth, nitrogen fixation, and cell parts, and SwaVid's step-by-step solutions explain them clearly.

### How should I write my answers to score full marks in Class 8 Science exams?

To score full marks, structure your answers clearly by defining key scientific terms and mentioning specific functions, such as the role of Rhizobium or the action of yeast. Referring to the structured answers in SwaVid's free PDF on this page will guide you on how to present your points accurately.

### Is the free PDF for this chapter aligned with the new NCERT book for the 2026-27 session?

Yes, the solutions are strictly based on the new NCERT book for the 2026-27 session following the NCF 2023 guidelines. You can easily access and download SwaVid's free PDF and step-by-step solutions directly from this page.

## Related pages

- [Class 8 Science chapters](https://www.swavid.com/science/class/8)

Solutions written by SwaVid, a personal AI tutor for Class 6 to 10 Maths and Science. Practise this chapter free: https://www.swavid.com/start/student