Year 7 Science · Unit 1 · Lesson 6
Challenge Worksheet
Learning Goals
1. Fill in the table: write each rule in your own words, and name who added it.
| Tenet | The tenet in your own words | Scientist(s) who added it |
|---|---|---|
| First | ||
| Second | ||
| Third |
Find the error
A student wrote this summary of how cell theory was built. Three sentences contain one error each. Write “correct”, or rewrite the sentence so it is correct.
| # | Student’s sentence | Correct, or the fixed sentence |
|---|---|---|
| 1 | In 1665, Antonie van Leeuwenhoek looked at a slice of cork and named the boxes he saw “cells”. | |
| 2 | The cork cells were dead: only their empty walls were left. | |
| 3 | Leeuwenhoek’s microscope stacked two lenses in a tube, which is why its picture was so sharp. | |
| 4 | Schleiden concluded that all plants are made of cells, and Schwann concluded the same for animals. | |
| 5 | Virchow agreed with Schleiden that new cells can form out of fluid, like crystals forming in water. |
2. Ella wants to add a fourth tenet: “All cells contain a nucleus.” Use what you learned about bacteria in Lesson 5 to explain why this cannot be a rule of cell theory.
Read the data
Scenario: what is made of cells?
Jo and Sam’s group put five specimens on slides: onion skin, pond water, cork, sand, and salt water that stood overnight. Table 1 records what they found.
| Sample | Cells seen? | What the class saw |
|---|---|---|
| Onion skin | yes | rows of box-shaped cells |
| Pond water | yes | small single cells swimming |
| Cork | yes | empty boxes with nothing inside |
| Sand | no | grains of rock |
| Salt water left overnight | no | small cube-shaped salt crystals had grown |
Source: sample class results.
3. Jo says: “Cork has cells, so cork must be alive.” Use Table 1 and what Hooke found to explain whether Jo is right.
4. Sam says: “The salt crystals grew out of the water overnight, so cells could form out of fluid the same way, just as Schleiden thought.” Use Table 1 and Virchow’s tenet to explain why Sam is wrong.
What if…?
Hooke’s microscope magnified about thirty times and was blurry at the edges. A drop of pond water would have shown him only a grey smear. What if, in 1665, Hooke had owned a lens as sharp as Leeuwenhoek’s best, and pointed it at pond water instead of cork?
5. Predict one way the history of cell theory might have changed. Then give one reason the full theory would still have needed later scientists.
6. Kai says: “Cell theory must be wrong, because it cannot tell us where the very first cell came from.” Evaluate Kai’s claim.
7. Viruses are not made of cells, and they can only make copies of themselves inside a living cell. Do viruses break the rules of cell theory? Consider the first and third tenets.
8. Cell theory took about 200 years to build, from Hooke’s cork to Virchow’s rule. Explain why it took so long, and what this tells us about how science works. Use specific examples from the history of cell theory.
Question 1
First: all living things are made of one or more cells (Schleiden and Schwann). Second: the cell is the basic unit of life (Schleiden and Schwann). Third: all cells come from existing cells (Virchow). [3 marks: 1 per row]
Find the error
1 Hooke, not Leeuwenhoek. 2 correct. 3 one ground glass bead (fewer lenses, less blur). 4 correct. 5 Virchow said cells come from cells. [5 marks]
Question 2
Bacteria are cells (1) with no nucleus (1); a tenet must hold for every cell (1). [3 marks]
Question 3
No: cork is dead bark, only empty walls (1); its cells show it was once alive (1). [2 marks]
Question 4
No cells were seen: crystals are non-living (1); growth alone is not life (1); tenet 3, a new cell forms only from an existing cell (1). [3 marks]
Question 5
Change: living cells seen earlier and called cells from the start (2). Still needed: proof all plants and animals have cells, and cells come from cells (1). [3 marks]
Question 6
Kai is wrong (1): the theory explains a tested pattern, new cells from old ones (1); how life began is a different question, not a flaw (1). [3 marks]
Question 7
No: tenet 1 is about living things, and viruses are mostly judged not alive (1); a virus is not a cell, so tenet 3 does not cover it (1); it needs cells to copy itself (1). [3 marks]
Question 8
Marking guide: 2 reasons (weak, blurry microscopes; many samples needed; wrong ideas such as cells from fluid); 2 three scientists in order; 1 building on or correcting earlier work; 1 conclusion about science. [6 marks]
Model answer: Hooke’s blurry lens showed dead walls; Leeuwenhoek saw living cells; much later Schleiden and Schwann checked many samples and Virchow overturned the fluid idea. Many people, better tools.
Common error: treating viruses as proof that cell theory is wrong.