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Class 8 Science: The Invisible Living World, 8 practice questions with answers

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These are 8 practice questions on the second chapter of the new NCERT Class 8 Science textbook, Curiosity: The Invisible Living World (subtitled Beyond Our Naked Eye). Each has a short answer and the textbook page it comes from. They cover telling a plant cell from an animal cell, what each part does, plant cells against animal cells, how a cell's shape suits its job, the levels of organisation, how much microscopes magnify, kinds of microbes, and microbes at work in idli batter. For a walk-through of how the book teaches science, see our Class 8 Science Chapter 1 explainer. Try each question before you read the answer.

These questions are our own, drafted with AI help. Every fact was checked against the page it cites by a test script, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

What the chapter says you need

Facts from the NCERT textbook (Curiosity, Grade 8, Chapter 2, printed pages 8 to 27):

Cells

Question 1. A student is shown two cells under a microscope. Cell X has a thick, firm outer layer, one large vacuole filling most of the cell, and many small green bodies. Cell Y has only a thin, flexible boundary, no green bodies and no large vacuole. One came from a leaf and one from the skin of a frog. (a) Which is which? Give three clues. (b) Name three parts that both cells will have.

Answer: (a) X is from the leaf, Y from the frog's skin; (b) the cell membrane, the cytoplasm and the nucleus. (a) Three clues point to a plant cell for X: the firm outer layer is a cell wall, which plant cells have outside the cell membrane and animal cells do not; the green bodies are plastids with the green pigment (chloroplasts), found only in plant cells; and plant cells usually have one large vacuole, while animal cells have small ones or none. Cell Y has none of these, so it is the animal cell, from the frog. (b) Both kinds of cell have a cell membrane around them, cytoplasm inside, and a nucleus that regulates all its activities. (Parts of plant and animal cells, pages 12 and 13.)

Question 2. Match each part of a cell with its job: cell membrane, cytoplasm, nucleus, cell wall. Jobs: (i) controls the cell's activities and its growth; (ii) where most life processes happen; (iii) gives a plant cell rigidity and strength; (iv) lets useful materials in and waste out.

Answer: cell membrane (iv); cytoplasm (ii); nucleus (i); cell wall (iii). The cell membrane is porous, so it lets in what the cell needs and lets out waste. Most of the life processes take place in the cytoplasm. The nucleus regulates the activities of the cell and its growth. The cell wall makes plant cells firm. (Parts of a cell, pages 12 and 13.)

Question 3. Give two differences between a plant cell and an animal cell, apart from the cell wall.

Answer: plant cells have plastids such as chloroplasts, and a large vacuole. Plant cells have tiny structures called plastids. Some of them, the chloroplasts, contain green chlorophyll for photosynthesis; animal cells have none. Plant cells also have a large vacuole that stores substances and helps keep the cell's shape; in animal cells vacuoles are usually absent, or small if present. (Plant and animal cells, page 13.)

Question 4. How does the shape of each of these cells suit its job? (a) A nerve cell. (b) A muscle cell in the food pipe. (c) A cheek cell.

Answer: (a) long and branched, to carry messages far and fast; (b) thin, flexible and spindle-shaped, to push food along; (c) thin and flat, to form a protective lining. (a) Nerve cells (neurons) are very long and branched, so messages travel quickly to and from every part of the body. (b) Muscle cells in the food pipe contract and relax in a wave, pushing food down to the stomach. (c) Cheek cells are thin and flat and line the inside of the mouth. (Variation in shape and structure, pages 13 and 14.)

Question 5. (a) Put these in order from the simplest to the most complex: the heart, a heart muscle cell, a human being, the circulatory system, heart muscle tissue. (b) In this chain for a plant, which level is missing, and what fills it? A leaf cell → leaf tissue → ___ → the shoot system → a mango tree.

Answer: (a) heart muscle cell → heart muscle tissue → heart → circulatory system → human being; (b) the organ, here a leaf. (a) A group of similar cells (heart muscle cells) forms a tissue; different tissues make up an organ, the heart; the heart works with other organs (the blood vessels) as an organ system, the circulatory system; and all the organ systems together make the organism. (b) Between tissue and organ system comes the organ: a leaf is an organ made of several tissues, and leaves, stems and buds together make the shoot system. (Levels of organisation, page 14.)

Microbes

Question 6. A cell is 0.05 mm across. How big would it look under (a) Hooke's microscope at 250 times, (b) a school microscope at 400 times, and (c) an electron microscope at 10,00,000 times?

Answer: (a) 12.5 mm; (b) 20 mm; (c) 50 m. Multiply the real size by the magnification. (a) 0.05 × 250 = 12.5 mm, a little over 1 cm. (b) 0.05 × 400 = 20 mm, that is 2 cm. (c) 0.05 × 10,00,000 = 50,000 mm, which is 50 m: that is why an electron microscope can show parts inside a cell. The chapter gives these magnifications: Hooke's microscope 200 to 300 times, a microscope for microbes 100 to 400 times, and an electron microscope about 10,00,000 times. (Pages 10, 17 and 24.)

Question 7. Sort these microbes into unicellular and multicellular: bacteria, protozoa such as Amoeba, yeast, bread mould. Which of them has no well-defined nucleus?

Answer: unicellular: bacteria, protozoa and yeast; multicellular: bread mould. Bacteria have no well-defined nucleus. Bacteria and protozoa are made of just one cell. Fungi can be either: yeast is a unicellular fungus and mould is multicellular. Bacteria have no well-defined nucleus or nuclear membrane; instead they have a nucleoid. Fungi have a cell wall, but with no chloroplasts they have no way to make food by photosynthesis. (Pages 23 and 24.)

Question 8. A family in Shimla soaks and grinds rice and urad dal in January and leaves the idli batter overnight, but in the morning it has hardly risen. The same recipe in Chennai rises well overnight. (a) Why the difference? (b) Which microbes do the work, and what do they give off that makes the batter rise? (c) What could the family in Shimla do?

Answer: (a) the microbes in the batter work slowly in the cold; (b) bacteria such as Lactobacillus, and yeast, which gives off carbon dioxide; (c) keep the batter somewhere warm. (a) Batter rises because microbes in it feed and multiply, and they grow well in warm conditions. A Shimla night in January is cold, so they hardly work; a Chennai night is warm, so they work fast. (b) Bacteria such as Lactobacillus, and yeast, a fungus, ferment the batter. Yeast breaks down food for energy and releases carbon dioxide, whose bubbles puff up the batter. (c) Keep the batter covered in a warm place, for example near the kitchen stove or wrapped in a cloth inside a closed box, or leave it longer. (Microorganisms in food: yeast and Lactobacillus, pages 20 and 21.)

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Sources

All opened and read on 2 November 2026. Page numbers are the printed page numbers of the textbook; printed page = PDF page + 7 for this chapter.

The facts are from the textbook pages above. The questions, answers and checks are our own. This guide is general information; follow your teacher and the textbook.

Practise with the worksheet: The Invisible Living World, Class 8 worksheet. Printable, in English, Hindi and Marathi, with an answer key.