Throughout the 1800s, scientists viewing organisms under microscopes made a series of observations.
A scientist viewing plant structures observed that plants are made up of very small repeating units. Each of these was surrounded by a wall and contained a nucleus.
A scientist examining tissue from tadpoles observed that animal structures are made up of repeating units. Each of these contained a nucleus.
A scientist viewing samples of pond water observed small, freely moving organisms. Each of these contained a single nucleus.
These observations led the scientists to develop a theory about living organisms. Which of the following conclusions about living things is best supported by these observations?
A.
All living things are made up of cells.
B.
Living things are made up of several different types of cells.
C.
Cells can only come from pre-existing cells.
D.
Cells from different living organisms look identical to one another.