Activities 2.4-2.6 — Microorganisms in Pond Water and Soil — "The Invisible Living World: Beyond Our Naked Eye"

1. 13 marksCuriosity Grade 8, Chapter 2, Activity 2.4, pages 15-16

   How do you observe pond or stagnant water under a microscope, and what do you find?

   Hint. One drop is enough.

   Method. Collect pond or stagnant water in a container, with the help of a teacher or an elder. Use a dropper to place a single drop on a microscope slide, put a coverslip over it, and observe.

   What you find. Tiny organisms, moving. The chapter's Table 2.1 records three kinds:

   Organism	Group	What is recorded
   Amoeba	Protozoa	Single cell, moving, irregular shape
   Paramecium	Protozoa	Single cell, moves from place to place using specialised structures
   Algae	—	Single cell, green because of a green pigment, moves using specialised structures

   Why a single drop suffices. These organisms are so numerous that one drop of ordinary pond water contains many of them. The water looks clear to the eye precisely because they are below the size the eye can resolve.

   Why an adult should collect it. Stagnant water can carry organisms that cause disease, so it should be handled with care and not touched unnecessarily.

   ✦ Answer: place one drop of pond water on a slide under a coverslip and observe — you find single-celled moving organisms such as Amoeba (irregular shape), Paramecium (moves with specialised structures) and green algae.

2. 24 marksCuriosity Grade 8, Chapter 2, Activity 2.5, pages 15-16

   Describe how a soil suspension is prepared and observed. Why is the mixture left to settle, and why is the drop taken from the top layer?

   Hint. The thing you want to see is far smaller than a grain of sand.

   Method. Collect moist soil from a field or garden in a beaker — using a spoon or gloves, never bare hands. Pour in water and stir with a glass rod. The dirty-looking liquid, holding very fine soil particles, is the soil suspension. Set it aside to settle. Then take a drop from the top layer with a dropper, place it on a slide, cover gently with a coverslip, and observe.

   Why let it settle. Coarse, heavy particles of sand and grit sink first. If you sampled immediately, the slide would be crowded with mineral grains that block the view and can crack the coverslip.

   Why take from the top. After settling, the top layer holds the finest suspended material — and the microorganisms, being extremely small and light, remain suspended there. So the top layer is where the organisms are relative to the debris.

   Why not bare hands. Soil contains many microorganisms, some of which can cause infection, especially through a cut.

   What you find. Small moving organisms similar to those in the pond water, which shows that even soil holds a variety of creatures invisible to the unaided eye.

   ✦ Answer: stir moist soil in water, let it settle so heavy grit sinks, then take a drop from the top layer, where the finest material and the microorganisms remain suspended — you see small moving organisms like those in pond water.

3. 33 marksCuriosity Grade 8, Chapter 2, Activity 2.6, Table 2.2, page 17

   What did the students record for the organisms found in the soil suspension?

   Hint. Four entries, and the last one lists several shapes.

   Table 2.2 records four kinds:

   Organism	Group	What was recorded
   Bread mould	Fungi	Branched filament without chlorophyll, having a sac-like structure
   Mould	Fungi	Branched filament without chlorophyll, having a brush-like structure
   Algae	—	Spherical, with chlorophyll — a green pigment
   Bacteria	—	Spherical, comma, spiral or rod-shaped, with one long hair-like structure and many small hair-like projections around the cell

   Two things worth extracting from the table.

   First, chlorophyll is the dividing line. Both fungi are noted as lacking it, and the algae as having it. That is why algae can make their own food using sunlight and fungi cannot — a point the chapter returns to when it says fungal cells have a cell wall but no chloroplasts.

   Second, bacteria have no single shape. Spherical, comma, spiral and rod forms all count as bacteria, so shape alone cannot identify them. The chapter had already noted that microorganisms, like plants and animals, vary in shape, size and structure.

   ✦ Answer: bread mould and mould (fungi — branched filaments without chlorophyll, with sac-like and brush-like structures), algae (spherical, with chlorophyll), and bacteria (spherical, comma, spiral or rod-shaped, with hair-like projections).

4. 42 marksCuriosity Grade 8, Chapter 2, Section 2.3, pages 15-17

   What are microorganisms? Give the meaning of the word and name the main categories.

   Hint. The word itself is two words joined.

   Definition. Microorganisms are the tiny creatures that cannot be seen with the naked eye. The chapter gives the word's construction directly: micro means very small and organisms means living beings. They are also called microbes.

   How many cells. Some are made of just one cell (unicellular) — bacteria and Amoeba, for instance. Others, like some fungi and algae, have many cells (multicellular).

   The main categories identified in the chapter: protozoa, algae, fungi and bacteria.

   Where they live. All around us — in water, soil, air, and even inside our body. Some survive extreme conditions such as hot water springs and snow-cold zones, as well as moderate temperatures.

   How they are seen. Only with a microscope, which magnifies them 100 to 400 times.

   ✦ Answer: microorganisms (microbes) are living beings too small to see with the unaided eye — micro = very small, organisms = living beings — and the main groups are protozoa, algae, fungi and bacteria, some unicellular and some multicellular.

5. 53 marksCuriosity Grade 8, Chapter 2, Ever heard of…, page 17

   What are viruses, and why are they described separately from bacteria, fungi and protozoa?

   Hint. The word 'acellular' is doing all the work.

   What the chapter says. Viruses are microscopic and acellular. They multiply when they enter a living cell. They may infect plants, animals or bacterial cells, and may cause disease.

   What 'acellular' means. Not made of a cell. Every other organism in this chapter — bacterium, alga, fungus, protozoan, plant, animal — is built from one or more cells. A virus is not.

   Why that forces separate treatment. The chapter's central claim is that the cell is the basic unit of life and that the body of every living organism is made of cells. A virus has no cell, so it does not fit inside that claim. Nor can it multiply on its own: the chapter's summary says viruses reproduce only inside the host organism, whereas bacteria, fungi and protozoa multiply by themselves given food, warmth and moisture.

   What this leaves open. Whether a virus should be called 'living' at all is a genuine question rather than a settled one — it shows the signs of life only when inside a host cell.

   ✦ Answer: viruses are microscopic and acellular — not made of cells — and they multiply only after entering a living cell, so they fall outside the rule that living organisms are built of cells, which is why the chapter lists them apart from bacteria, fungi and protozoa.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity - Textbook of Science for Grade 8 (hecu102.pdf), Chapter 2 'The Invisible Living World: Beyond Our Naked Eye', pages 8-27, Reprint 2026-27. HAND-WRITTEN throughout. Page count verified against the printed contents page (hecu1ps.pdf p.18): 20 pages, 8-27, matching exactly. Covers the 3 'Probe and ponder' prompts (p.8), all 9 activities (2.1 to 2.9), every in-text section (2.1 to 2.5), the 9 numbered 'Keep the curiosity alive' exercises (pp.25-26) and the 4 'Discover, design, and debate' projects (p.27). EXERCISE Q1 VENN DIAGRAM READ OFF A 500-DPI RENDER of p.25: three circles labelled 'Only in Animal Cell' (top), 'Only in Bacterial Cell' (lower left) and 'Only in Plant Cell' (lower right), with an arrow labelling the central three-way overlap 'Common to all three cells'. Each of those four labelled regions carries two ruled lines; the three PAIRWISE overlap regions carry none. Working from the book's own statements (p.13 'the cell wall in the plant cell provides rigidity'; p.24 'bacteria do not have a well-defined nucleus... instead they have a nucleoid'; and the Snapshots line 'Plant, fungal, and bacterial cells have an extra covering, called a cell wall'), the correct placement is: cytoplasm and cell membrane in the three-way overlap (exactly two items, matching the two ruled lines); chloroplast in plant-only; nucleoid in bacterial-only; NUCLEUS in the animal-plant pairwise overlap (plant cells have nuclei, bacteria do not); CELL WALL in the plant-bacterial pairwise overlap (not plant-only, since the book says bacterial and fungal cells have walls too); and NO listed part is unique to the animal cell. The solution states both traps explicitly. FACTUAL FIGURES TAKEN VERBATIM FROM THE BOOK: Hooke's Micrographia 1665, microscope 200-300x, cork, honeycomb, first use of 'cell'; Leeuwenhoek 1660s, Father of Microbiology; ordinary microscope 100-400x; electron microscope about 10,00,000x; ostrich egg yolk 130-170 mm as the largest known cell; Ananda Mohan Chakrabarty 1938-2020, oil-degrading bacterium 1971, patent 1980; biogas mainly carbon dioxide with a high proportion of methane; one of India's oldest biogas plants late 1850s; microalgae produce more than half of Earth's oxygen; Spirulina over 60 per cent protein by body weight and a source of vitamin B12, harvested after 3-6 weeks. The MNRE biogas-programme project answer deliberately does NOT assert current programme details - it names the programmes to search for and tells the student to verify against the current official MNRE page, since names and subsidy rules change.. Questions are referenced from the NCERT textbook for identification.