What is Invisible Living World Exercises in Class 8 Science NCERT?

The Class 8 Science NCERT Chapter 2 — Invisible Living World: Beyond Our Naked Eye exercise section tests students on all the key concepts covered in the chapter, including NCERT exercises, microorganisms questions, competency-based questions, assertion reason. It includes multiple-choice questions…

What does the NCERT Class 8 Science Invisible Living World: Beyond Our Naked Eye exercise section cover?

The Class 8 Science NCERT Chapter 2 u2014 Invisible Living World: Beyond Our Naked Eye exercise section tests students on all the key concepts covered in the chapter, including NCERT exercises, microorganisms questions, competency-based questions, assertion reason. It includes multiple-choice questions (MCQs), assertion-reason questions, short-answer questions, long-answer questions, and competency-based questions that align with the NCERT Curiosity textbook. Working through these exercises helps Class 8 students reinforce their conceptual understanding, prepare for classroom assessments, and build exam readiness for CBSE school tests. Each question links back to a specific section of the chapter so students can revise the theory alongside the practice.

How should Class 8 students approach the Invisible Living World: Beyond Our Naked Eye exercises?

Class 8 students should approach the Invisible Living World: Beyond Our Naked Eye exercises by first revising the main theory and definitions from each part of the chapter, especially around NCERT exercises and microorganisms questions. Start with the MCQs and assertion-reason questions to quickly test recall, then attempt the short-answer questions that need a one or two-line explanation, and finally tackle the long-answer and competency-based questions that require applying concepts to new situations. Write neat diagrams wherever the question involves a process, cycle, or setup, and always use NCERT-style vocabulary in your answers to match CBSE marking schemes.

Are these Invisible Living World: Beyond Our Naked Eye questions competency-based as per NEP 2020?

Yes, the Invisible Living World: Beyond Our Naked Eye exercise set follows the NEP 2020 competency-based education (CBE) framework used by CBSE and NCERT for Class 8 Science. Instead of only asking students to recall definitions, many questions are scenario-based and require applying the concept to real-life situations, analysing data, or evaluating claims. This matches Bloom's Taxonomy levels L3 (Apply), L4 (Analyse), and L5 (Evaluate), going beyond rote learning. Students practising these questions build the higher-order thinking skills that modern CBSE school exams increasingly assess, and also prepare well for competitive foundation tests in later years.

Which NCERT Curiosity sections are tested in Chapter 2 exercises?

The Chapter 2 u2014 Invisible Living World: Beyond Our Naked Eye exercise set systematically tests every major section of the NCERT Curiosity Class 8 Science textbook for this chapter. Topics covered include NCERT exercises, microorganisms questions, competency-based questions, assertion reason. Every in-text question, activity-linked question, and end-of-chapter question from the Curiosity book is represented, so students can be confident that completing this exercise set gives them full coverage of the NCERT syllabus. Teachers also frequently pick questions from these sections for school unit tests and half-yearly exams, making thorough practice essential for strong performance.

How do assertion-reason questions work in this Class 8 Science chapter?

Assertion-reason questions in the Class 8 Science Invisible Living World: Beyond Our Naked Eye exercise set present two statements u2014 an Assertion (A) and a Reason (R) u2014 and ask students to judge whether each is true and whether R correctly explains A. Students pick from four standard options: both true with R explaining A, both true but R not explaining A, A true and R false, or A false. This format tests whether Class 8 learners genuinely understand the cause-and-effect relationships behind NCERT exercises, not just surface facts. Mastering this format is valuable because CBSE Class 10 board exams use the same pattern.

What is the best revision strategy before attempting these exercises?

The best revision strategy before attempting Invisible Living World: Beyond Our Naked Eye exercises is to read through all theory parts of NCERT Curiosity Chapter 2 once, write down the key terms such as NCERT exercises, microorganisms questions, competency-based questions, assertion reason in your own words, and then re-do all activities mentally to understand the underlying concept. Next, make a one-page mind map linking the main ideas. Only then attempt the exercise questions u2014 first without looking back, then self-correcting. This active-recall approach builds much stronger long-term memory than repeatedly re-reading the textbook, and is widely recommended by CBSE teachers for Class 8 Science preparation.

What does the NCERT Class 8 Science Invisible Living World: Beyond Our Naked Eye exercise section cover?

The Class 8 Science NCERT Chapter 2 — Invisible Living World: Beyond Our Naked Eye exercise section tests students on all the key concepts covered in the chapter, including NCERT exercises, microorganisms questions, competency-based questions, assertion reason. It includes multiple-choice questions (MCQs), assertion-reason questions, short-answer questions, long-answer questions, and competency-based questions that align with the NCERT Curiosity textbook. Working through these exercises helps Class 8 students reinforce their conceptual understanding, prepare for classroom assessments, and build exam readiness for CBSE school tests. Each question links back to a specific section of the chapter so students can revise the theory alongside the practice.

How should Class 8 students approach the Invisible Living World: Beyond Our Naked Eye exercises?

Class 8 students should approach the Invisible Living World: Beyond Our Naked Eye exercises by first revising the main theory and definitions from each part of the chapter, especially around NCERT exercises and microorganisms questions. Start with the MCQs and assertion-reason questions to quickly test recall, then attempt the short-answer questions that need a one or two-line explanation, and finally tackle the long-answer and competency-based questions that require applying concepts to new situations. Write neat diagrams wherever the question involves a process, cycle, or setup, and always use NCERT-style vocabulary in your answers to match CBSE marking schemes.

Are these Invisible Living World: Beyond Our Naked Eye questions competency-based as per NEP 2020?

Yes, the Invisible Living World: Beyond Our Naked Eye exercise set follows the NEP 2020 competency-based education (CBE) framework used by CBSE and NCERT for Class 8 Science. Instead of only asking students to recall definitions, many questions are scenario-based and require applying the concept to real-life situations, analysing data, or evaluating claims. This matches Bloom's Taxonomy levels L3 (Apply), L4 (Analyse), and L5 (Evaluate), going beyond rote learning. Students practising these questions build the higher-order thinking skills that modern CBSE school exams increasingly assess, and also prepare well for competitive foundation tests in later years.

Which NCERT Curiosity sections are tested in Chapter 2 exercises?

The Chapter 2 — Invisible Living World: Beyond Our Naked Eye exercise set systematically tests every major section of the NCERT Curiosity Class 8 Science textbook for this chapter. Topics covered include NCERT exercises, microorganisms questions, competency-based questions, assertion reason. Every in-text question, activity-linked question, and end-of-chapter question from the Curiosity book is represented, so students can be confident that completing this exercise set gives them full coverage of the NCERT syllabus. Teachers also frequently pick questions from these sections for school unit tests and half-yearly exams, making thorough practice essential for strong performance.

How do assertion-reason questions work in this Class 8 Science chapter?

Assertion-reason questions in the Class 8 Science Invisible Living World: Beyond Our Naked Eye exercise set present two statements — an Assertion (A) and a Reason (R) — and ask students to judge whether each is true and whether R correctly explains A. Students pick from four standard options: both true with R explaining A, both true but R not explaining A, A true and R false, or A false. This format tests whether Class 8 learners genuinely understand the cause-and-effect relationships behind NCERT exercises, not just surface facts. Mastering this format is valuable because CBSE Class 10 board exams use the same pattern.

What is the best revision strategy before attempting these exercises?

The best revision strategy before attempting Invisible Living World: Beyond Our Naked Eye exercises is to read through all theory parts of NCERT Curiosity Chapter 2 once, write down the key terms such as NCERT exercises, microorganisms questions, competency-based questions, assertion reason in your own words, and then re-do all activities mentally to understand the underlying concept. Next, make a one-page mind map linking the main ideas. Only then attempt the exercise questions — first without looking back, then self-correcting. This active-recall approach builds much stronger long-term memory than repeatedly re-reading the textbook, and is widely recommended by CBSE teachers for Class 8 Science preparation.

TOPIC 6 OF 50

Invisible Living World — Exercises

🎓 Class 8 Science CBSE Theory Ch 2 — Microorganisms: Friend and Foe ⏱ ~26 min

🌐 Language: [gtranslate]

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This MCQ module is based on: Invisible Living World — Exercises

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[myaischool_lt_science_assessment grade_level="class_8" science_domain="biology" difficulty="basic"]

Chapter Summary — Key Points

Our eyes cannot see objects below a certain size. Lenses (curved transparent materials shaped like lentil seeds) bend light to magnify small objects.
A water-filled round-bottom flask acts like a simple magnifying glass, demonstrating how curved surfaces refract light.
Antonie van Leeuwenhoek (1600s) built early microscopes and was the first to observe microscopic organisms, which he called "animalcules."
Modern compound microscopes use multiple lenses to magnify objects 100 to 400 times or more.
All living organisms are made of cells — the basic structural and functional units of life.
Every cell has three main parts: cell membrane (porous outer boundary), cytoplasm (jelly-like material containing nutrients), and nucleus (control centre).
Plant cells additionally have a rigid cell wall outside the cell membrane.
Microorganisms (microbes) are found everywhere — in air, water, soil, and inside our bodies.
Microorganisms are classified into five groups: Bacteria, Fungi, Algae, Protozoa, and Viruses.
Pond water organisms include: Amoeba (pseudopodia), Paramecium (cilia), Euglena (flagellum), and Spirogyra (spiral chloroplast).
Bacteria come in four shapes: coccus (spherical), bacillus (rod), vibrio (comma), spirillum (spiral).
Viruses are acellular (not made of cells) and can only reproduce inside living host cells.
Lactobacillus bacteria convert milk into curd through fermentation — producing lactic acid that coagulates milk proteins.
Yeast (a fungus) produces CO₂ in bread dough, making it rise. Fermented Indian foods include idli, dosa, and dhokla.
Rhizobium bacteria live in root nodules of leguminous plants and fix atmospheric nitrogen into usable form — the basis of crop rotation.
Microalgae (Spirulina, Chlorella, Diatoms) produce over 50% of Earth's oxygen and are used as health supplements.
Some microorganisms are pathogens — they cause diseases (e.g., common cold by virus, food poisoning by bacteria, athlete's foot by fungus).
Hygiene, clean water, vaccination, and proper food handling prevent microbial diseases.

Keywords

LensCurved transparent material that bends light

MicroscopeInstrument using lenses to magnify tiny objects

CellBasic unit of all living organisms

Cell MembranePorous outer boundary of a cell

CytoplasmJelly-like material inside the cell

NucleusControl centre of the cell

MicroorganismTiny living being visible only under microscope

BacteriaSingle-celled organisms without true nucleus

FungiOrganisms without chlorophyll (yeast, mould)

AlgaePlant-like organisms with chlorophyll

ProtozoaAnimal-like single-celled organisms

VirusAcellular agent; reproduces only in host cells

FermentationConversion of sugar by microbes (e.g., lactic acid)

LactobacillusBacterium that converts milk to curd

RhizobiumNitrogen-fixing bacterium in legume roots

Nitrogen FixationConverting atmospheric N₂ to usable form

MicroalgaeMicroscopic photosynthetic organisms

PathogenDisease-causing microorganism

Keep the Curiosity Alive — Exercises

Q1. L1 Remember Study the cell diagram below and label the following parts in the correct positions: nucleus, cytoplasm, cell membrane, cell wall, chloroplast, nucleoid.

Answer:
A: Cell Wall — the rigid outermost boundary (found in plant cells only)
B: Cell Membrane — the porous boundary just inside the cell wall
C: Cytoplasm — the jelly-like material filling the cell interior
D: Chloroplast — the green organelle where photosynthesis occurs (plant cells only)
E: Nucleus — the large, membrane-bound control centre of the cell
F: Nucleoid — a region within the nucleus (in some contexts, nucleoid refers to the DNA-containing region in bacterial cells that lack a true membrane-bound nucleus)

Q2. L4 Analyse Anamoli set up two test tubes for an experiment:

Test Tube A: Sugar solution + a pinch of yeast, with a balloon stretched over the mouth.
Test Tube B: Sugar solution only (no yeast), with a balloon stretched over the mouth.
Both test tubes were placed in a warm spot for 3 to 4 days.

After 3 to 4 days, Anamoli observed that the balloon on Test Tube A had inflated (puffed up), while the balloon on Test Tube B remained flat.

Answer the following questions:

(a) Before starting the experiment, predict what will happen to each balloon after 3-4 days.
(b) Could the warm atmosphere alone have expanded the air inside the balloon to cause it to inflate? Explain.
(c) Did the yeast produce a gas? Which gas do you think it is?
(d) Did the sugar react with warm air to produce a gas? How does Test Tube B help answer this question?

(a) Prediction: The balloon on Test Tube A (with yeast) should inflate because yeast feeds on sugar and releases a gas. The balloon on Test Tube B (without yeast) should remain flat because there is no organism to break down the sugar.

(b) No, the warm atmosphere alone cannot explain the inflation. If warmth was the cause, both balloons would have inflated equally since both test tubes were kept in the same warm conditions. Since only balloon A inflated and balloon B remained flat, the gas must have been produced by something present only in Test Tube A — that is, the yeast.

(c) Yes, the yeast produced a gas. The gas is carbon dioxide (CO₂). Yeast carries out fermentation — it feeds on sugar and produces CO₂ and a small amount of alcohol as by-products. The CO₂ gas accumulated inside the test tube and inflated the balloon.

(d) Sugar did NOT react with warm air to produce gas. Test Tube B serves as a control — it contains the same sugar solution in the same warm conditions but without yeast. Since balloon B remained flat, we can conclusively say that it was the yeast (not the sugar or warm air) that produced the gas. This is the value of a controlled experiment.

Q3. L4 Analyse After the yeast experiment, a student carefully removes the balloon from Test Tube A (which is filled with gas). She transfers this gas into a test tube containing clear lime water by gently squeezing the balloon. She observes that the lime water turns milky.

(a) What is the student trying to find out?
(b) What does the milky lime water confirm about the identity of the gas?
(c) Write the name of the gas produced by yeast during fermentation.

(a) The student is trying to identify the gas produced by yeast during fermentation. Specifically, she wants to confirm whether the gas is carbon dioxide (CO₂).

(b) The lime water test is a standard chemical test for carbon dioxide. When CO₂ is passed through clear lime water (calcium hydroxide solution), it reacts to form calcium carbonate, which is insoluble and appears as a white precipitate — making the solution look milky. The fact that the lime water turned milky confirms that the gas is carbon dioxide (CO₂).

(c) The gas produced by yeast during fermentation is carbon dioxide (CO₂). This is the same gas that makes bread dough rise — the CO₂ bubbles get trapped in the dough, creating the soft, airy texture.

Discover, Design, and Debate

Q4. L2 Understand History of Biogas in India: India has a long history with biogas production. One of the oldest biogas plants was established in the late 1850s. In more recent times, the Ministry of New and Renewable Energy has promoted the National Biogas Programme to encourage rural households to produce clean cooking fuel from animal waste and organic matter.

(a) What are the main raw materials used for biogas production?
(b) Which type of microorganism breaks down organic waste to produce biogas?
(c) Name one advantage of biogas over traditional firewood for cooking.

(a) The main raw materials for biogas production are animal dung (cow dung is most common), crop residues, food waste, and other organic matter. These are mixed with water in a biogas plant (digester).

(b) Anaerobic bacteria (bacteria that function without oxygen) break down the organic waste in the sealed digester. They decompose the complex organic compounds and produce a mixture of gases — primarily methane (CH₄) and carbon dioxide (CO₂) — collectively called biogas.

(c) Advantages of biogas over firewood include: (1) Biogas burns more cleanly, producing much less smoke and air pollution than firewood — this improves indoor air quality and reduces respiratory diseases. (2) Biogas is a renewable energy source that can be continuously produced from waste. (3) Using biogas reduces deforestation caused by cutting trees for firewood. (4) The leftover material (slurry) from the biogas plant can be used as organic fertiliser.

Q5. L3 Apply Fermented Food Items: Many communities across India have traditional fermented foods. In Northeast India, fermented soybeans (known as "kinema" or "akhuni") are a staple ingredient. Fermented bamboo shoots are another popular traditional food used in various dishes.

(a) Name any three fermented foods commonly consumed in India (from different regions).
(b) What role do microorganisms play in the preparation of these foods?
(c) Why are fermented foods often considered more nutritious than their unfermented counterparts?

(a) Three examples: (1) Idli and Dosa (South India) — fermented rice and urad dal batter. (2) Dhokla (Gujarat) — fermented chickpea flour. (3) Kinema/Akhuni (Northeast India) — fermented soybeans. Other examples include curd/dahi (pan-India), kanji (Rajasthan), and enduri pitha (Odisha).

(b) Microorganisms (primarily bacteria and yeast) break down complex carbohydrates and proteins in the food into simpler compounds during fermentation. They produce gases (making batters fluffy), organic acids (giving tangy flavour), and various other compounds that change the taste, texture, and nutritional profile of the food.

(c) Fermented foods are often more nutritious because: (1) Fermentation breaks down complex nutrients into simpler, more easily digestible forms. (2) Microorganisms produce additional vitamins (especially B-vitamins) during the process. (3) Fermentation can reduce anti-nutritional factors (substances that block nutrient absorption) present in raw ingredients. (4) The beneficial bacteria in fermented foods can act as probiotics, supporting gut health.

Q6. L3 Apply Study Mushroom Parts: Obtain a fresh mushroom (available in any vegetable market). Carefully examine its different parts using a magnifying glass or, if available, a microscope.

(a) List the main visible parts of a mushroom and describe each briefly.
(b) Mushrooms are classified as fungi, not plants. Give two reasons why mushrooms are not considered plants.
(c) Describe the basic steps involved in mushroom cultivation.

(a) Main visible parts of a mushroom:
- Cap (Pileus): The umbrella-shaped top part. Its underside may have gills (thin blade-like structures) or pores.
- Gills (Lamellae): Thin, radiating blade-like structures under the cap where spores are produced.
- Stalk (Stipe): The stem-like structure that supports the cap above the ground.
- Ring (Annulus): A skirt-like remnant of tissue that sometimes appears on the stalk (not present in all mushrooms).
- Mycelium: Thread-like network of filaments (hyphae) usually hidden underground — this is the main body of the fungus.

(b) Two reasons mushrooms are not plants: (1) Mushrooms lack chlorophyll and cannot carry out photosynthesis — they do not make their own food. Instead, they absorb nutrients from decaying organic matter or from living organisms. (2) Mushrooms do not have true roots, stems, or leaves. Their body is made of thread-like hyphae (filaments), which is fundamentally different from plant tissue.

(c) Basic steps in mushroom cultivation: (1) Prepare the substrate — straw, sawdust, or other organic material is cleaned, moistened, and sometimes pasteurised (heated to kill competing organisms). (2) Inoculate with spawn — mushroom spawn (mycelium grown on grain) is mixed into the substrate. (3) Incubation — the inoculated substrate is kept in a dark, humid, warm space for the mycelium to spread through it (2-3 weeks). (4) Fruiting — conditions are adjusted (increased humidity, lower temperature, some light) to trigger mushroom growth. (5) Harvesting — mature mushrooms are picked by hand when their caps are fully formed.

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