Year 7 Science · Unit 1 · Lesson 06

Cell Theory

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Learning Goals

Apply the three tenets of cell theory to explain real-world scientific discoveries.
Justify why each scientist's contribution was necessary to build the complete theory.
Predict what science would look like if a different theory had prevailed.

Warm Up

Predict + Reason

Scenario

Before Rudolf Virchow's contribution in 1855, many scientists believed that cells could arise spontaneously from non-living matter — a theory called spontaneous generation. If this idea had remained the accepted scientific theory instead of cell theory, scientists would have continued to believe that new cells can form out of fluids or other non-living substances without needing a parent cell.

(a) Predict: What impact would accepting spontaneous generation have had on medicine and our understanding of disease?

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(b) Justify: Why does cell theory (specifically the third tenet) give us a better explanation? Use what cell theory actually tells us in your answer.

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Your Turn

Real-world context

In 2020, scientists used CRISPR gene-editing technology to modify the DNA inside human cells to potentially cure sickle cell disease — a condition where red blood cells are misshapen and cannot carry oxygen properly. The treatment, developed by researchers including teams at the Broad Institute in the United States, required detailed knowledge of how cells divide and pass on genetic information. The first patients showed remarkable results, with some appearing completely cured by 2023.

(a) Explain which tenet of cell theory made this CRISPR treatment possible. Why does the fact that "all cells come from pre-existing cells" matter for curing a disease like sickle cell?

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(b) Why couldn't this treatment have been developed without the knowledge built by Schleiden, Schwann, and Virchow? Refer to specific contributions from at least two of these scientists.

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Show What You Know

1. A classmate says: "Cell theory was invented by one brilliant scientist who figured it all out." Using evidence from this lesson, explain why this statement is incorrect.

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2. When Leeuwenhoek sent letters to scientists in London describing living cells, many refused to believe him for years. Using the three tenets of cell theory, explain why his discovery was so important — and why it might have seemed unbelievable at the time.

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Wrap Up

In one sentence, what was the main idea of this lesson?