Name ______________________________ Date ______________ Period 1 2 3 4 5 6 7 8
The Discovery of Cells
Before microscopes were invented, people believed that diseases were caused by curses and
supernatural spirits. They had no idea that organisms such as bacteria existed. As Scientists
began using microscopes, they quickly realized that they were entering a new world – one of
microorganisms. Microscopes enable scientists to view and study cells. Cells are the basic units
of living organisms.
Robert Hooke was an English scientist who lived at the same time as van Leeuwenhoek. Hooke
used a microscope to study cork, the dead cells of oak bark. In cork, Hooke observed small
geometric shapes. Hooke gave these box-shaped structures the name “cells” because they
reminded him of the small rooms monks lived in at a monastery.
Cells are the basic building blocks of all living things. In the 1830’s, the German scientist
Schleiden, observed a variety of plants and concluded that all plants are composed of cells.
Another scientist named Schwann observed the same thing in animals. The observations and
conclusions of these scientists are summarized as the cell theory, one of the fundamental ideas of
modern biology.
The cell theory is made up of three main ideas:
1. All organisms are composed of one or more cells.
2. The cell is the basic unit of organization of organisms – all cells have a specific job.
3. All new cells come from old cells.
Answer the following questions:
1. What is a cell?
2. What is cork?
3. What specifically did scientists study in order to develop the cell theory?
4. What is a microorganism?
5. How do you think an old cell makes a new cell?