Cell Theory

How are cells the basic unit of structure and function for life?

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How was the cell theory developed?

A scientist places a single cell in a petri dish. The scientist observes the dish over the next two days and counts the number of cells, collecting the data in Table 1.

The scientist’s experiment was most likely about which part of the cell theory?

• The cells grown in a petri dish all come from preexisting cells.

• The number of cells grown in a petri dish will double every 12 hours.

• The cells grown in a petri dish will only survive for 48 hours.

• Single-celled organisms can grow in a petri dish.

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Which statement is not a part of cell theory?

• All cells come from preexisting cells.

• Cells can only be viewed with a microscope.

• All organisms are made up of one or more cells.

• Cells are the basic unit of life.

A scientist is conducting an experiment. She puts water with nutrients into a flask. She then seals the flask. After leaving the flask to sit for two weeks, she finds there are no cells in the mixture. What statement best demonstrates the principle of cell theory accounting for the results?

• The nutrients are substances that are nonliving.

• The sealed flask did not allow cells to get oxygen, so they did not reproduce.

• Since the mixture did not start with any cells, there were none present to reproduce.

• There were not enough nutrients for the cells to survive for two weeks, so they all died.

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Which statements are included in the cell theory? Select the correct answers. 

• All organisms are made of one or more cells.

• Cells can only be seen by using a microscope.

• Cells are the basic unit of structure and function.

• All cells come from pre-existing cells.

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A group of students discuss some observations they made under the microscope. Which statement would be least useful in a discussion about cell theory?

• I observed a single celled organism moving across the slide.

• I was able to see that both plants and animals are made of smaller units called cells.

• I saw cells in the process of dividing and creating new cells.

• I could see that the cells were different shapes and sizes.

A scientist does an experiment. They put one bacteria cell in a test tube with nutrients, and close the tube. They count the number of cells in the tube after one day. The graph shows the results of the experiment.

Which principle of the cell theory is best demonstrated by the results of the experiment?

• Bacteria cells change over time.

• All organisms are made of one or more cells.

• Cells are the basic unit of structure and function.

• All cells come from pre-existing cells.

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Many people used to believe in spontaneous generation, the idea that living things could form from non-living matter. Why did Rudolf Virchow's ideas help put an end to this belief?

• He was the first to coin the term cell.

• He showed that both plants and animals are made of cells.

• He discovered that cells must come from pre-existing cells.

• He invented the electron microscope.

Which piece of technology played an important role in developing the cell theory?

• computer

• gene therapy

• microscope

• laser