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Cell: The Building Block of Life: CBSE Class 9 Biology practice questions

Practise 50 questions on Cell: The Building Block of Life, free, with an explanation for each answer.

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Sample questions

A microscope has a 10X eyepiece and a 40X objective lens. What is the total magnification?

A compound light microscope
  1. 4X
  2. 50X
  3. 4000X
  4. 400X
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D. 400X

Total magnification =10×40=400= 10 \times 40 = 400X. An object looks 400 times larger than it really is. Adding the powers (50X) or dividing them (4X) are common slips.

Through the eyepiece, the round field of view is 4 mm across. You count 20 onion peel cells in a straight line across it (along the diameter). Estimate the size of one cell.

A microscope field of view 4 mm across with a row of 20 onion cells along its diameter
  1. 0.2 µm
  2. 20 µm
  3. 200 µm
  4. 80,000 µm
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C. 200 µm

Field diameter = 4 mm = 4×1000=40004 \times 1000 = 4000 µm. Cell size=4000 μm20=200 μm\text{Cell size} = \frac{4000\ \mu\text{m}}{20} = 200\ \mu\text{m} 0.2 µm comes from forgetting the unit conversion, and 80,000 µm from multiplying instead of dividing.

In the potato experiment, the piece in Beaker A weighed 50 g at the start and 56 g after an hour. By what percentage did its weight increase?

Two beakers: A with plain water and B with 20% salt solution, each holding a potato piece
  1. 6%
  2. 10.7%
  3. 12%
  4. 112%
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C. 12%

56−5050×100=12%\frac{56 - 50}{50} \times 100 = 12\% Plain water is less concentrated than the potato cells, so water entered the cells by osmosis and the piece gained weight. 6% is just the gain in grams, 10.7% divides by the final weight instead of the initial one, and 112% is the final weight as a percentage of the start.

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