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

NCERT Probe and Ponder Questions (Page 8)

Question 1.
Have you ever wondered what you might see if the invisible world around you became visible?

Answer:

Yes, it would be truly fascinating to observe microorganisms such as bacteria, fungi, protozoa, and viruses that are always interacting with our environment and living within our bodies. It would completely shift our perspective on cleanliness, health, and the intricate ecosystems that surround us.

Question 2.

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’?

Answer: 

Yes, it would be truly fascinating to observe microorganisms such as bacteria, fungi, protozoa, and viruses that are always interacting with our environment and living within our bodies. It would completely shift our perspective on cleanliness, health, and the intricate ecosystems that surround us.

Question 3.

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

Answer: Yes, microorganisms are always interacting—some live in symbiotic partnerships, while others compete for resources or even prey on each other. For instance, certain bacteria aid digestion while others cause illness, and fungi break down organic material, improving soil quality. Such interactions are essential to many ecological processes.

Keep the Curiosity Alive (Pages 25-26)

Question 1.
Various parts of a cell are given below. Write them in the appropriate places in the following diagram.

1. Nucleus

2. Cytoplasm

3. Chloroplast

4. Cell wall

5. Cell membrane

6. Nucleoid

Answer:

Nucleus: Present in both plant and animal cells (absent in bacteria); it regulates all cell activities.
Cytoplasm: A jelly-like material that fills the cell and holds the organelles.
Chloroplast: Found only in plant cells; it carries out photosynthesis.
Cell wall: Present in plant and bacterial cells, forming their outermost protective layer.
Cell membrane: Present in every cell; in plants and bacteria it lies just beneath the cell wall, while in animals it forms the outer boundary.
Nucleoid: Found only in bacterial cells; this region contains DNA because bacteria lack a true nucleus.

Question 2.

Aanandi took two test tubes and marked them A and B. She put two spoonfuls of sugar solution in each of the test tubes. In test tube B, she added a spoonful of yeast. Then she attached two incompletely inflated balloons to the mouth of each test tube. She kept the setup in a warm place, away from sunlight.

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

(a) Water evaporated in test tube B and filled the balloon with the water vapour.

(b) The warm atmosphere expanded the air inside test tube B, which inflated the balloon.

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

(d) Sugar reacted with warm air, which produced gas, eventually inflating the balloon.

(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?

Answer:

(i) (c) Yeast generated a gas in test tube B, which caused the balloon to expand.
Explanation: The yeast fermented the sugar and released carbon dioxide (CO₂), and this gas filled the balloon, making it swell.

(ii) She wants to check if the gas formed is carbon dioxide (CO₂). If the lime water becomes milky, it confirms CO₂ is present, as the gas reacts with lime water to produce calcium carbonate.

Question 3.

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?

Answer:

Beans are leguminous plants that develop a symbiotic partnership with Rhizobium bacteria found in their root nodules. These bacteria convert atmospheric nitrogen into a usable form in the soil, supplying natural nitrogen to the crop. Hence, the second farmer does not need to use nitrogen-rich fertilisers.

Question 4.

Snehal dug two pits, A and B, in her garden. In pit A, she put fruit and vegetable peels and mixed them 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?

Answer:

She is examining how well composting works.

In Pit A, the combination of green waste (fruit and vegetable peels) and dry leaves creates the right carbon–nitrogen balance required for proper decomposition.
Pit B does not have this balance, so the waste will break down more slowly and may produce an unpleasant smell.

This experiment demonstrates that microorganisms decompose materials more effectively when both carbon-rich and nitrogen-rich components are available.

Question 5.
Identify the following micro-organisms:

(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.

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

Question 6.
Devise an experiment to test that microorganisms need optimal temperature, air, and moisture for their growth.

Answer:

Arrange three bread slices as follows:

Slice A: Placed in a warm, moist spot (near the sink)
Slice B: Kept in a dry, sealed container
Slice C: Stored in a cold environment (refrigerator)

After three days, you will notice that Slice A shows the most fungal growth.

Conclusion: Microorganisms thrive when conditions such as temperature, moisture, and air supply are favorable.

Question 7.

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

Answer: A bread slice kept near the sink will develop mold, whereas slices stored in the refrigerator will show little to no growth.
Reason: The warm, moist environment near the sink supports microbial growth, while the cold conditions inside the refrigerator slow it down or prevent it altogether.

Question 8.

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

Answer: Lactic acid bacteria keep multiplying in the curd and produce increasing amounts of lactic acid, which causes the curd to taste more sour.

Higher temperatures accelerate bacterial activity, leading to faster acid formation and greater sourness.

Question 9.

Observe the set-up given in Figure 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?

(in) What would happen if yeast were not added to flask A?

Answer:

(i) Yeast breaks down the sugar in the warm solution, generating carbon dioxide gas along with a small amount of alcohol.

(ii) The lime water in test tube B becomes milky because the CO₂ released in flask A passes through the delivery tube into flask B and reacts with the lime water, confirming that carbon dioxide is present.

(iii) Without warm conditions, fermentation would not take place, so no carbon dioxide would form. Consequently, the lime water in test tube B would stay clear.

Key Concepts of The Invisible Living World

Understanding the Invisible Living World in Class 8 Science helps students explore microorganisms, cell structure, and their essential roles. Grasping these fundamental principles supports stronger exam performance and builds a foundation for future biology studies.

By reviewing the NCERT Solutions (2025-26) for Chapter 2, learners can reinforce key facts about unicellular and multicellular organisms, their functions, and the amazing utility of microbes in the environment and food production.

For best exam results, regularly revise cell basics and microbe functions. Focus on labelled diagrams, activities, and real-life applications to make learning engaging and maximize your Science marks in Class 8.