Cell Theory & Discovering Cells — Practice · Grade 7 Science

Chapter: Cells, Transport & Cellular Energy

What this practice covers

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

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

Vocabulary used: cell, cell theory, unicellular, multicellular, cell division.

Problem 1

Does cell theory require every organism to have many cells?
Answer and explanation

No. A single cell can be an organism; many organisms contain multiple cells.

Problem 2

Why is cork a limited model of a living cell?
Answer and explanation

Much of the living content is absent; the observed compartments mainly show remaining cell walls.

Problem 3

What other information is needed to infer mass from cell count?
Answer and explanation

Cell sizes and composition matter. More cells do not supply a complete mass measurement by themselves.

Problem 4

Why can a bacterium be an organism without organs?
Answer and explanation

One cell can carry out the required interacting life processes; organs are arrangements in some multicellular organisms.

Problem 5

Illustrative record: a living cell divides into two cells; each later divides once. A student claims the resulting four cells must be four times the original mass. Use cell theory to explain the number change and evaluate the mass claim.
Answer and explanation

The sequence fits new cells arising from existing cells and gives four cells after the two division rounds. The mass claim is unsupported: cells can differ in size, and growth requires material uptake. Cell count alone does not establish four times the starting mass. Additional mass or size observations would be needed.

Count one to two to four cells.

Connect new cells with previous cells dividing.

Distinguish cell production from total mass.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A newly observed unicellular organism has no tissue. Does that contradict cell theory?
Answer and explanation

No. Unicellular organisms consist of one cell that carries out life processes. Tissues are not required in every organism.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which fits cell theory?
  1. Every cell has chloroplasts
  2. All organisms contain many cells
  3. New cells arise from existing cells
  4. Every living cell has an enclosed nucleus
Answer and explanation

New cells arise from existing cells

Cell theory includes cells arising from existing cells; the other statements are not universal.

Problem 8

Starting with two cells, each divides once and then each resulting cell divides once. How many cells result?
Answer and explanation

8 cells

Two becomes four, then eight, assuming every stipulated division occurs.

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