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Class 9 Science: Cell, The Building Block of Life, 8 practice questions with answers

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These are 8 practice questions on Chapter 2, Cell: The Building Block of Life, of the new NCERT Class 9 Science textbook, Exploration (First Edition, April 2026). Each has a short worked answer and the textbook page it comes from. They cover who first saw a cell, the Cell Theory, ribosomes, osmosis, meiosis, and three numericals on the size of a cell under a microscope. Try each one on paper before you open the answer.

These questions are our own, drafted with AI help. Every number was re-computed 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 (Exploration: Science, Textbook for Grade 9, Chapter 2, printed pages 8 to 27):

History and parts of the cell

Question 1. In 1665, who became the first to see a cell? (J. J. Thomson; Isaac Newton; or Robert Hooke.)

Answer: Robert Hooke. Robert Hooke saw cells in 1665 with a microscope he designed himself. He looked at a thin slice of cork and named the small box-like compartments "cells". (Page 9.)

Question 2. Which scientist, in 1855, added to the Cell Theory that new cells form only from pre-existing cells? (Rudolf Virchow; Robert Hooke; or Matthias Schleiden.)

Answer: Rudolf Virchow. Schleiden (plants, 1838) and Schwann (animals, 1839) showed that living things are made of cells; Virchow (1855) added that new cells come only from pre-existing cells. (Page 23.)

Question 3. Which part of a cell is the site of protein synthesis? (Golgi apparatus; ribosome; lysosome; or vacuole.)

Answer: the ribosome. Ribosomes are the protein factories of the cell; they may lie free in the cytoplasm or be attached to the endoplasmic reticulum. (Page 17.)

Osmosis and cell division

Question 4. A plant cell has less dissolved salt inside it than a 4 per cent salt solution has. It is kept in that 4 per cent salt solution for an hour and is then moved into pure water. In each case, does water move into the cell or out of it, and why?

Answer: in the salt solution water moves out of the cell; in pure water it moves back in. The cell membrane is selectively permeable: it lets water through but not the salt. In osmosis, water moves from the more dilute side to the more concentrated side. The 4 per cent solution is more concentrated than the cell contents, so water leaves the cell. Pure water is more dilute than the cell contents, so water enters the cell. (Selectively permeable membrane and osmosis, pages 11 and 12.)

Question 5. What does meiosis produce from one parent cell? (Two daughter cells, each with the same number of chromosomes; four daughter cells, each with the same number of chromosomes; or four daughter cells, each with half the number of chromosomes.)

Answer: four daughter cells, each with half the number of chromosomes. In meiosis the parent cell divides twice, making four daughter cells, each with half as many chromosomes. Mitosis makes two identical cells. (Pages 21 and 22; summary, page 24.)

Size of a cell under the microscope

Use 1 mm = 1000 µm (page 10), and image size = actual size × magnification (page 10).

Question 6. Under a microscope, 28 cells of a leaf peel fit in one line across the circular field of view, and each cell is about 85 µm across. What is the diameter of the field of view, in mm?

Answer: 2.38 mm. The field's diameter is the number of cells across it times the size of one cell: 28 × 85 µm = 2380 µm. Since 1 mm = 1000 µm, this is 2380 ÷ 1000 = 2.38 mm. (This runs the chapter's cell-size method, field diameter ÷ number of cells, backwards; Activity 2.1, page 10.)

Question 7. A cell 30 µm wide is seen through a lens that magnifies 300 times. How wide does it appear, in mm?

Answer: 9 mm. Image size = 30 µm × 300 = 9000 µm, and 1000 µm = 1 mm, so it appears 9 mm wide. (Page 10.)

Question 8. A bacterium is about 1 µm long, and the unaided eye cannot see anything smaller than about 0.1 mm. (a) Write 0.1 mm in µm. (b) What is the least magnification that makes the bacterium appear 0.1 mm long? (c) A school microscope magnifies 400 times: how long does the bacterium appear through it, in mm? (d) Can the eye see it then?

Answer: (a) 0.1 mm = 100 µm. (b) 100 ÷ 1 = at least 100 times. (c) 1 µm × 400 = 400 µm = 0.4 mm. (d) Yes: 0.4 mm is bigger than the 0.1 mm limit of resolution of the eye. (Limit of resolution, page 9; conversion and magnification, page 10.)

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Sources

All opened and read on 21 October 2026. Page numbers are the printed page numbers of the textbook; printed page = PDF page + 7.

The facts and definitions are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.