Discover, Design and Debate — Projects — "The Invisible Living World: Beyond Our Naked Eye"

1. 14 marksCuriosity Grade 8, Chapter 2, Discover, design, and debate, page 27

   India has a long history of biogas production, and one of our oldest biogas plants was set up in the late 1850s. Find out about the Biogas Programme initiated by the Ministry of New and Renewable Energy, Government of India.

   Hint. This is a look-up task — the useful part is knowing what to look up and how to check it.

   What the chapter itself supplies. India has a long history of biogas production, and one of our oldest biogas plants was set up in the late 1850s. Earlier in the chapter you learned what biogas is: mainly carbon dioxide with a high proportion of methane, released by bacteria decomposing waste in an oxygen-free environment, and usable for cooking, heating, electricity and vehicles.

   What to find out, and where. Go to the Ministry of New and Renewable Energy (MNRE) website, which is the authoritative source. Search for the national biogas programme — over the years it has run under names such as the National Biogas and Manure Management Programme and, later, the New National Biogas and Organic Manure Programme. Programme names, scales and subsidy rules change, so check the current official page rather than relying on a textbook or a summary (including this one).

   Questions worth answering in your write-up:

   • What sizes of plant does the programme support — household, community, or larger?
   • What feedstock is used: cattle dung, kitchen waste, agricultural residue?
   • What does a family get from a plant — cooking gas, and manure as a by-product?
   • What support is offered, and who is eligible?
   • How many plants have been set up in your own state?

   Connect it back to the science. A biogas plant is a controlled version of Activity 2.7: the same decomposition by microorganisms, but sealed away from air so the bacteria that work without oxygen dominate and produce methane, with the residue left over as manure.

   ✦ Answer: look this up on the MNRE website, noting plant sizes, feedstock, outputs (gas plus manure), support offered and numbers in your state — and record which programme name and which year your figures come from, since these change; the chapter's own contribution is that one of India's oldest biogas plants dates from the late 1850s.

2. 24 marksCuriosity Grade 8, Chapter 2, Discover, design, and debate, page 27

   Fermented foods like fermented soya bean and fermented bamboo shoots are traditional in parts of India. With help from your parents and teachers, list traditional fermented foods from your area and investigate their ingredients, method of preparation, the microorganism responsible, and their cultural and nutritional importance.

   Hint. You already know two of the organisms — the chapter named them.

   Start from what the chapter has already given you. Two microorganisms have been named as food-fermenters:

   • Yeast (a fungus) — releases carbon dioxide, making dough rise and turn fluffy, plus a little alcohol; used for breads, cakes, pastries
   • Lactobacillus (a bacterium) — produces lactic acid, which sets milk into curd and makes it sour; it also ferments the batter for idli and dosa and the dough for bhatura

   How to build your list. Ask at home and in your neighbourhood, since fermented foods are regional and often prepared without anyone calling them 'fermented'. The chapter's own examples are fermented soya bean and fermented bamboo shoots; idli, dosa, bhatura and curd are already in the text.

   Record for each food:

   What to record	What to look for
   Ingredients	The sugar or starch the microbes feed on
   Method	Is it kept warm? Covered? For how long?
   Organism	Does it rise (gas → yeast) or turn sour (acid → bacteria)?
   Cultural importance	Festivals, seasons, who traditionally prepares it
   Nutritional importance	Keeping quality, digestibility, taste

   A useful rule for identifying the organism. If the food puffs up or rises, a gas is being produced and yeast is likely involved. If it becomes sour without rising, an acid is being produced and bacteria such as Lactobacillus are likely. Many foods show both.

   Be careful about claims. Say what you were told and by whom. If nobody knows which organism is responsible, write that down rather than guessing — an unanswered question is a legitimate result.

   ✦ Answer: survey your own region for fermented foods and record ingredients, method, responsible microorganism, and cultural and nutritional importance for each — using the rule that rising means gas (yeast) and souring means acid (bacteria such as Lactobacillus), and recording honestly where the answer is not known.

3. 33 marksCuriosity Grade 8, Chapter 2, Discover, design, and debate, page 27

   Study the different parts of a macro fungus, a mushroom, using a magnifying glass and a microscope. With help from senior students, explore the internal structure of the different parts under the microscope in your school laboratory.

   Hint. You already know how to make a slide — Activities 2.2 and 2.3 gave you the method.

   Why a mushroom is worth this attention. It is a fungus, like the moulds in Table 2.2 and like yeast — but where yeast is unicellular, a mushroom is a multicellular fungus large enough to hold in your hand. It is the same kingdom at a completely different scale, which makes the comparison instructive.

   With the magnifying glass, look at the outside: the cap, the stalk, and the closely packed sheets on the underside of the cap. Note their arrangement and how regularly spaced they are.

   Under the microscope, use the slide-making method you already know from Activity 2.2 — take a very thin piece, mount it in a drop of water or glycerin to stop it drying, lower the coverslip slowly so no air bubbles are trapped, and stain if the structures are too pale to see. Take a thin section from the stalk and another from the underside of the cap, and compare.

   What to look for, and what you should be able to predict. From the chapter, fungal cells have a cell wall but no chloroplasts, so a mushroom cannot make its own food by photosynthesis — which is exactly why mushrooms are not green and why they grow on decaying material rather than in sunlight. Table 2.2 describes moulds as branched filaments; look for whether the mushroom's tissue is built of threads too.

   Draw what you see, not what you expect. That was the instruction in Activity 2.3, and it matters more here, since you will be looking at unfamiliar structures.

   Safety. Study mushrooms bought as food or supplied by your school. Never collect wild mushrooms to handle or taste, since some are poisonous and cannot be reliably identified by appearance.

   ✦ Answer: examine the cap, stalk and the sheets under the cap with a magnifying glass, then mount thin sections as in Activity 2.2 and look for the branched filaments typical of fungi — predicting from the chapter that you will find cell walls but no chloroplasts, which is why a mushroom cannot photosynthesise and lives on decaying matter.

4. 43 marksCuriosity Grade 8, Chapter 2, Discover, design, and debate, page 27

   Interact with an entrepreneur and learn the steps for cultivation of mushroom.

   Hint. The chapter gives a parallel worked example — the Spirulina steps on page 23.

   Use the Spirulina model as your template. The chapter sets out mushroom cultivation as a task to investigate, but it does give a fully worked cultivation example for Spirulina, and its structure tells you what to ask about:

   1. Prepare a suitable container or space
   2. Control the light and temperature
   3. Supply the growing medium
   4. Introduce the living organism
   5. Maintain it during growth
   6. Harvest after a stated period

   Questions to put to the grower, following that structure:

   Stage	What to ask
   Growing medium	What material is used, and how is it prepared?
   Starting material	Where is the spawn obtained, and how is it introduced?
   Conditions	What temperature, humidity and light are needed? Why is darkness or shade used?
   Time	How long from spawning to first harvest? How many harvests?
   Problems	What goes wrong — contamination by other moulds, pests, wrong humidity?
   Economics	Cost to start, price obtained, where it is sold

   Connect it to the science you know. Mushrooms are fungi, so they need what the chapter says microorganisms need — suitable temperature and moisture — and they cannot photosynthesise, which is why they are grown on prepared organic material in shade rather than in sunlight like a crop. Contamination is a live risk precisely because, as the chapter says, microorganisms are everywhere.

   Write it up honestly. Record what the grower actually told you, note where practices differ from what you expected, and mark anything you could not verify.

   ✦ Answer: interview a grower using the six-stage structure of the Spirulina example — medium, spawn, conditions, maintenance, harvest time and problems — and relate the answers to the chapter's science: fungi need warmth and moisture, have no chloroplasts so are grown in shade on organic material, and are vulnerable to contamination because microorganisms are everywhere.

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.