Cell Theory & the Discovery of Cells — Practice · Grade 10 Science

Chapter: Cells, Membranes & Exchange

What this practice covers

By the end of Cell Theory & the Discovery of Cells you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: cell, cell theory, magnification, resolution, spontaneous generation, organism.

Problem 1

Which statement is NOT one of the three tenets of cell theory?
  1. All living things are made of one or more cells
  2. The cell is the basic unit of structure and function
  3. All cells arise from pre-existing cells
  4. All cells contain a nucleus
Answer and explanation

All cells contain a nucleus

Prokaryotic cells (like bacteria) have no nucleus, so 'all cells contain a nucleus' is false and is not part of cell theory.

Problem 2

A researcher wants to see individual ribosomes, which are about 20 nanometers across. Why won't the best light microscope work?
  1. Its resolution limit (~200 nm) is far larger than a ribosome, so it cannot separate that fine detail no matter how much it magnifies
  2. Light microscopes cannot magnify past 100×
  3. Ribosomes are too large to fit in the field of view
  4. Light microscopes only work on living cells
Answer and explanation

Its resolution limit (~200 nm) is far larger than a ribosome, so it cannot separate that fine detail no matter how much it magnifies

Magnification and resolution are different. A light microscope's resolution stalls near 200 nm, so a 20 nm ribosome stays a blur; an electron microscope is needed.

Problem 3

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

400 ×

Total magnification = eyepiece × objective = 10 × 40 = 400×.

Problem 4

Explain why disproving spontaneous generation was essential to completing cell theory.
Answer and explanation

Cell theory's third tenet says cells only come from pre-existing cells. If life could arise spontaneously from non-living matter, that tenet would be false. Pasteur's swan-neck experiment showed sterile broth stayed lifeless until microbes reached it, confirming that cells come only from other cells.

Problem 5

Who is credited as among the first to observe living, single-celled organisms?
  1. Robert Hooke
  2. Antonie van Leeuwenhoek
  3. Matthias Schleiden
  4. Louis Pasteur
Answer and explanation

Antonie van Leeuwenhoek

Leeuwenhoek's unusually powerful lenses let him observe living 'animalcules' in pond water in the 1670s.

Problem 6

A cell image spans 25 mm on paper and is labeled 500×. Estimate actual length. Explain the reasoning in your own words.
Answer and explanation

About 50 μm if the printed image retains its stated scale.

Actual size=image size/magnification=25/500=0.05 mm.

Convert 0.05 mm to 50 μm.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

Why did improved microscopy matter to cell theory? Show the reasoning, not just the conclusion.
Hints

An instrument extends observation but conclusions still require evidence.

Answer and explanation

It allowed structures and cell division to be observed and compared across organisms.

Problem 8

Does one empty microscope field prove a sample contains no cells?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Sampling, preparation, focus and resolution can limit detection; inspect appropriate fields and controls.

Problem 9

Enlarging an unresolved feature does not create new detailEnlarging an unresolved feature does not create new detailMagnification aloneBetter resolutionResolution: distinguish nearby features, not simply make a blur bigger.
Original resolution comparison, not a calibrated microscope test; the two-panel scale isolates the conceptual distinction.
Interpret the supplied visual. Why would enlarging a blurry photograph not establish that two nearby structures are one?
Answer and explanation

The original image may lack sufficient resolution; resizing cannot recover detail that was never resolved. Use an appropriate method or independent evidence.

Magnification is enlargement of an image. Resolution is the ability to distinguish nearby features as separate under the imaging conditions. A larger blurry spot can still hide two structures. Contrast, preparation, staining and artifacts also influence what can be seen. Light and electron imaging have different capacities and preparation requirements; neither one automatically shows every structure alive and unchanged. Before identifying an organelle, ask whether the feature is resolved, labeled with scale and supported by appropriate observations rather than a familiar-looking blob.

The original image may lack sufficient resolution; resizing cannot recover detail that was never resolved. Use an appropriate method or independent evidence.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 10

A cell spans 2.4 lengths of a 25 μm scale bar. Find its estimated length and explain why a resized “400×” label is less useful than the correctly resized bar.
Answer and explanation

The estimate is 2.4×25 = 60 μm. A magnification label describes a particular display enlargement; resizing changes it, while an image and scale bar resized together preserve the specimen-length ratio.

The estimate is 2.4×25 = 60 μm. A magnification label describes a particular display enlargement; resizing changes it, while an image and scale bar resized together preserve the specimen-length ratio.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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