When scientists set out to test a hypothesis, it is often most practical to try to prove the hypothesis false rather than to prove it is true in all cases. Scientists place great confidence in cell theory, yet it has not been tested in every living thing on the planet. 

What piece of evidence would cause scientists to decide that cell theory would need to be revised? 

• An organism was found with tissues made of something other than cells. 

• A cell was found that could continue to divide and reproduce indefinitely. 

• An animal cell was found that could harness solar energy as plant cells do. 

• Cells were found that used something other than DNA as hereditary material. 

In the past, some scientists accepted the theory of spontaneous generation. This theory states that organisms can arise from nonliving matter. Now scientists generally accept cell theory to explain the origin and growth of new organisms. Which of these statements is a key idea of cell theory that disproves the theory of spontaneous generation? 

• The cell is the basic unit of life. 

• All living things are made of matter. 

• All cells arise from pre-existing cells by division. 

• All cells are formed from the combination of two other cells. 

Under a microscope, a series of cells are observed that lack membrane-bound 

internal organelles. Which of these is the most likely cell type? 

• Plant cell 

• Animal cell 

• Eukaryotic cell 

• Prokaryotic cell 

Bacteria are prokaryotic cells. By contrast, animal, plant, and fungal cells are eukaryotic. 

What is the main difference between prokaryotes and eukaryotes? 

• Eukaryotes have a cell wall. 

• Prokaryotes cannot live without a host. 

• Eukaryotes copy DNA and are able to reproduce. 

•  Prokaryotes do not have a membrane-bound nucleus. 

 

Many different microscopic organisms can be found in pond ecosystems, including the three organisms shown in the diagrams below. The primary cellular structures in each of these single-celled organisms are labeled in the diagrams. Some of the structures are common to all three organisms and other structures are not. 

Which of the following identifies the organisms that are eukaryotic and gives the best explanation?  

•  organisms 1 and 2 only, because both have a nucleus  

• organisms 2 and 3 only, because both use flagella 

•  organisms 1, 2, and 3, because they all have ribosomes 

•  organisms 1, 2, and 3, because they are all single celled 

A student looks at a cell under a microscope. Which of the following observations would indicate that the cell is from a plant rather than an animal? 

•  a nucleus located inside of the cell 

•  numerous cilia on the outside of the cell 

•  chloroplasts in the cytoplasm of the cell 

• a thin membrane around the edge  of the cell