Week 9 - Characteristics of Living Things

4 Cells and the Microscope

Lesson 4

Science in Action 8
Pages 98-102, 439-440

ScienceFocus 8
Pages 103-106, 111-114

Lesson 4: Cells and the Microscope

Background Information

Cell Theory
Today, most scientists accept the cell theory. The major ideas of the cell theory are:
- All living things are made of one or more cells.
- Cells are the basic units of structure and function in living things.
- All cells come from other cells.

However, what are cells? Let's begin to answer this question by looking at how cells were discovered. The following is a timeline indicating some of the people and events in the development of the cell theory.

1665 Robert Hooke looked at thin slices of cork under a microscope. Hooke stated that the cork was similar to a honeycomb with lots of empty spaces. He used the word "cells" to describe the cavities in the cork because they reminded him of the small rooms, called cells, found in monasteries. Today, scientists know that Hooke was not looking at a living cell. He was, however, observing the walls of cells that were alive at one time.

1680 Anton van Leeuwenhoek was the first to examine a drop of pond water under the microscope and observed several microorganisms that he called "beasties."

1824 Henri Dutrochet was the first to describe the cell as the truly fundamental part of the living organism.

1833 Robert Brown discovered and named the central part of the cell. He called it the nucleus.

1838 Matthias Schleiden determined that all plants are made up of cells.

1839 Theodor Schwann determined that all animals are made up of cells.

1859 Rudolf Virchow concluded that all plant and animal cells arise for other living cells.

The work of these and many other scientists lead to the development of the cell theory. A theory is an attempt to explain a set of observations. The surest way to test a theory is to use it as the basis of a prediction and then check it by experimentation. An important effect of a theory is to spur scientists to search for new data. When new data are found, the theory is reexamined. If the new data do not support the theory, then the theory must be revised or discarded. In science, a theory is never proved once and for all. The theory, however, does account for new evidence that arises. The development of the cell theory could not have occurred without the invention and improvement of the technology called the microscope . The microscope allowed biologists (scientists who study living things) to study organisms in greater detail than ever before.

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