Question Opening prompt 1
What might we see if the tiny living world around us became visible?
Steps only
A microscope reveals tiny organisms and details hidden from the unaided eye.
Answer
We would see a diverse microscopic world around us.
CLASS 8 · SCIENCE · CHAPTER 2
The Invisible Living World: Beyond Our Naked Eye
Simple answers to chapter activities and in-text questions, all nine review questions, opening prompts, and four projects.
41 worked answersComplete chapter answers
41 worked answers · short steps first, explanations when you need them
Probe and Ponder
Textbook pages 8
Question Opening prompt 2
How could seeing this hidden world change our ideas about size, complexity, or what counts as living?
Steps only
Small organisms can be complex; even one cell can carry out life processes.
Answer
Being tiny does not mean something is simple or non-living.
Question Opening prompt 3
How might tiny living beings interact with one another?
Steps only
Microbes can compete, feed, cooperate, or decompose dead matter.
Answer
Microorganisms interact in different ways depending on their surroundings.
Question Opening prompt 4
Share one question you have about the invisible living world.
Steps only
Ask a specific question that can be explored safely with evidence.
Answer
Example: What microorganisms live in a drop of pond water?
Activities and In-text Questions
Textbook pages 9–23
Question Activity 2.1
What happens to letters seen through a round-bottom flask filled with water, and why?
Steps only
Water-filled flask as a lens
Answer
The letters look larger through the water-filled flask. Its curved glass and water bend light like a simple lens. A real magnifying glass also makes small details appear larger.
Question Activity 2.2
What do onion-peel cells look like under a microscope, and how are they like bricks in a wall?
Steps only
Onion cells
Answer
Onion-peel cells usually look rectangular and are arranged closely, like bricks in a wall. Each cell is a small unit of the plant. With an adult or teacher, view a prepared slide; do not handle stains or glass slides without supervision.
Question Activity 2.3
What can be observed in cheek cells, and how are they different from onion cells?
Steps only
Cheek cells
Answer
Cheek cells are usually flat or irregular in shape. They have a cell membrane, cytoplasm, and nucleus, but no cell wall. Onion cells also have these basic parts, plus a cell wall that gives them a more regular shape. A teacher should prepare and supervise microscope slides.
Question Activity 2.4
What might be seen in a drop of pond or stagnant water under a microscope?
Steps only
Pond or stagnant water
Answer
You may see tiny moving organisms, such as protozoa, or small algae. What you see depends on the water sample. Collect and view it with an adult or teacher, and wash hands afterward.
Question Activity 2.5
What may a microscope show in a drop from a soil suspension?
Steps only
Soil suspension
Answer
A drop may contain tiny organisms or moving specks that cannot be seen clearly with the naked eye. Soil contains many small living things. Use a spoon or gloves for soil and have a teacher prepare the slide.
Question Activity 2.6
How can students record what they find in pond water and soil suspension?
Steps only
Recording microorganisms
Answer
Make a simple observation table with: sample, what was seen, movement, shape, and a possible group such as protozoa, algae, fungi, or bacteria. Record only what the microscope shows; ask a teacher to help identify organisms because many microbes look similar.
Question Activity 2.7
What changes may happen to fruit and vegetable peels buried in soil for two to three weeks?
Steps only
Plant waste and manure
Answer
The peels may become darker, softer, and crumbly. Soil microorganisms, including fungi and bacteria, break the waste into simpler materials. This process is decomposition, and the resulting natural manure returns nutrients to the soil. Results depend on warmth and moisture.
Question Activity 2.8
How does dough with yeast compare with dough without yeast after a few hours, and why?
Steps only
Yeast and dough
Answer
The dough with yeast usually rises and becomes softer or more spongy. Yeast uses sugar and releases carbon dioxide, whose bubbles make the dough expand. Warmth helps yeast work. The dough without yeast rises much less. Do not eat classroom samples.
Question Activity 2.9
What is likely to happen to lukewarm milk kept warm compared with cold milk kept cool after adding a little curd?
Steps only
Making curd in different conditions
Answer
The lukewarm milk kept warm is more likely to thicken into curd. Lactobacillus bacteria grow and ferment milk sugar, producing lactic acid. Cold slows their activity, so the cold sample may take longer to set. Use clean bowls and do not taste samples used for an experiment.
Question In-text: eyesight and lenses
Why can’t the unaided eye see very tiny organisms clearly, and how does a lens help?
Steps only
Seeing small objects
Answer
The eye can only resolve objects above a certain size. A curved lens bends light so a small object appears larger, making details easier to see. A microscope uses lenses to magnify very small objects further.
Question In-text: cell parts
What do the cell membrane, cytoplasm, nucleus, and plant cell wall do?
Steps only
Jobs inside a cell
Answer
- Cell membrane: surrounds the cell and controls what enters and leaves.
Question In-text: cell variation
Do cells have different shapes? Give examples and explain why.
Steps only
Different cell shapes
Answer
Yes. Cells have shapes that suit their jobs. A nerve cell is long and branched to carry messages; a muscle cell can contract; cheek cells are thin and flat. Plant cells often have a firm wall.
Question In-text: body organisation
How do cells help the body perform different jobs?
Steps only
Cells working together
Answer
Similar cells work together as a tissue. Tissues form organs, organs work together in organ systems, and organ systems make an organism. For example: muscle tissue in the food pipe contracts to move food towards the stomach.
Question In-text: microorganisms
What are microorganisms, and which groups are studied in this chapter?
Steps only
What counts as a microorganism?
Answer
Microorganisms are living things too small to be seen clearly without magnification. The chapter describes bacteria, protozoa, microscopic algae, and fungi. They live in many places, including water and soil.
Question In-text: our connection to microbes
Where can microbes be found, how can they reach food, and how do they affect us?
Steps only
Helpful and harmful microbes
Answer
Microbes live in air, water, soil, food, and on living things. They can reach exposed food from hands, surfaces, or the air. Some help us, for example in digestion, fermentation, and decomposition; some spoil food or cause disease.
Question In-text: preservation
Why do salt, sugar, and oil help preserve pickles or murabba?
Steps only
Pickles and murabba
Answer
A large amount of salt or sugar makes it difficult for many microbes to grow because less usable water is available to them. A layer of oil also helps keep air and moisture away from the pickle surface. Use clean, dry utensils to avoid adding water or microbes.
Question In-text: decomposition
Why do gardeners collect dry leaves and plant waste in a pit?
Steps only
Why gardeners collect leaves
Answer
Microorganisms break down the waste into simpler, nutrient-rich manure. The manure returns nutrients to the soil. Keeping the waste in a suitable, slightly moist place helps decomposition.
Question Be a Scientist
How can specially selected microorganisms help clean some polluted places?
Steps only
Microbes and pollution
Answer
Some microorganisms can break down particular pollutants, such as certain oil compounds. Scientists study and select suitable microbes, then check that using them is safe and effective. One microorganism cannot clean every kind of pollution.
Question In-text: no microorganisms
What might happen if microorganisms did not exist on Earth?
Steps only
A world without microorganisms
Answer
Dead plants, animals, and food waste would break down much more slowly, so waste would build up.
Question In-text: useful microbes
Name some problems that microorganisms can help solve.
Steps only
Problems microbes can help solve
Answer
Decomposing waste and making compost.
Question In-text: microalgae
How can microalgae help aquatic environments and people?
Steps only
Microalgae in water
Answer
Microalgae use sunlight to make food and release oxygen.
Question In-text: cell as a basic unit
Why is a cell called the basic unit of life?
Steps only
Why cells are basic units of life
Answer
All living things are made of one or more cells.
Question In-text: food fermentation
How do microorganisms help make foods such as curd and bread?
Steps only
Microorganisms in food
Answer
Lactobacillus bacteria change milk sugar into lactic acid, which helps milk set into curd.
Keep the Curiosity Alive
Textbook pages 25–26
Question 1
Place nucleus, cytoplasm, chloroplast, cell wall, cell membrane, and nucleoid in the appropriate regions of the plant, animal, and bacterial cell diagram.
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Membrane and cytoplasm: all. Nucleus: plant and animal. Cell wall: plant and bacteria. Chloroplast: plant. Nucleoid: bacteria.
Answer
Place shared parts in overlaps and specialised parts in the matching cell regions.
Question 2
Sugar solution is placed in two tubes; yeast is added only to B, and balloons are fitted. (i) What may happen after 3–4 hours, and why? (ii) What does passing the gas into limewater test?
Steps only
Yeast ferments sugar and releases CO₂; CO₂ turns limewater milky.
Answer
The yeast tube’s balloon inflates, and its gas makes limewater milky.
Question 3
Why might one farmer add nitrogen-rich fertiliser to wheat while a neighbouring farmer grows beans without adding nitrogen fertiliser?
Steps only
Rhizobium in legume root nodules fixes nitrogen for the plant.
Answer
Beans can get nitrogen help from Rhizobium; wheat usually needs soil nitrogen supplied.
Question 4
Why did Snehal mix dried leaves with food peels in one covered pit but not the other? What is she testing?
Steps only
The pits compare decomposition with and without dry leaves.
Answer
Dry leaves can improve the conditions for composting microbes.
Question 5
Identify: (i) lives in many environments and in the gut; (ii) makes bread and cakes soft and fluffy; (iii) lives in pulse-crop root nodules and helps provide nutrients.
Steps only
Match each clue to a familiar microorganism.
Answer
- (i) Bacteria
- (ii) Yeast
- (iii) Rhizobium
Question 6
Design an experiment to test whether microorganisms need suitable temperature, air, and moisture to grow.
Steps only
Compare identical samples while changing warmth, moisture, or air one at a time.
Answer
Record growth without opening or touching samples that may contain mould.
Question 7
One bread slice is kept near a sink and another in a refrigerator. What may you observe after three days, and why?
Steps only
Mould usually grows faster in warm, moist conditions than in a refrigerator.
Answer
The slice near the sink may mould sooner.
Question 8
Why might curd become more sour when left out for a day? Give two possible explanations.
Steps only
Bacteria make lactic acid; warmth can speed their activity.
Answer
More fermentation can make curd taste sourer.
Question 9
In a setup, warm sugar solution and yeast in flask A are connected to limewater in tube B. (i) What happens in A? (ii) What happens in B after four hours and why? (iii) What if yeast is not added?
Steps only
Yeast ferments sugar, releasing CO₂ that turns limewater milky.
Answer
Without yeast, little gas is expected and limewater stays clearer.
Question Question-making activity
Prepare questions using prompts such as why, when, how long, where, and why not, based on what you have learned.
Steps only
Turn a chapter idea into a clear, investigable question.
Answer
Answers vary; make the question specific and safe.
Discover, Design, and Debate
Textbook pages 27
Question Project 1
Find information about India’s biogas programme and explain how a biogas plant can help a community.
Steps only
Organic waste makes biogas; the gas is fuel and the leftover slurry can be manure.
Answer
Biogas can support waste management and local energy. Check current scheme details with MNRE.
Question Project 2
Find a traditional fermented food from your area and describe its ingredients, preparation, microbes, and cultural or nutritional importance.
Steps only
Ask about a local food, its ingredients, fermentation steps, and microbes.
Answer
Use a local example and verify the microorganism with a reliable source.
Question Project 3
How can you study the parts of a mushroom using a magnifying glass or microscope?
Steps only
Observe and draw the cap, stalk, and underside with adult guidance.
Answer
Use a safe specimen; never taste or handle unidentified wild mushrooms.
Question Project 4
What steps are involved in mushroom cultivation? Interview a local grower or entrepreneur.
Steps only
Prepare substrate, add spawn, maintain suitable clean conditions, and harvest at the right time.
Answer
Ask a local grower for species-specific steps and safety advice.