Back

Cell Theory (Write out the questions and the answers.)
The discovery of cells was made possible by the development of the microscope in the 17th century. In 1665, the English scientist Robert Hooke used a microscope to examine a thin slice of cork. Hooke described it as consisting of “a great many little boxes.” These “little boxes” reminded him of the cubicles or “cells” in which monks lived, so he called them cells. What Hooke had observed were actually the remains of dead plant cells. The first person to observe living cells was a Dutch trader, Anton van Leeuwenhoek. Although van Leeuwenhoek’s microscope was rather simple, in 1673 it was powerful enough to enable him to view the world of microscopic organisms which had never before been seen.
About 150 years passed before scientists began to organize the observations begun by Hooke and van Leeuwenhoek into a unified theory known as the cell theory. This theory has three parts:
(1) All living things are composed of one or more cells.
(2) Cells are the basic units of structure and function in an organism.
(3) Cells come only from the reproduction of existing cells.

1. What caused scientists to discover the existence of cells?
2. What are the small rooms that monks lived in called?
3. What did Hooke observe in the cork slice?
4. What discovery is van Leeuwenhoek noted for?

5. What are the three parts of the cell theory?

Early evidence for the cell theory was provided by German scientists. In 1838, the botanist Matthias Schleiden concluded that all plants are composed of cells. A year later, the zoologist Theodor Schwann came to the same conclusion about animals. In 1855,
Rudolf Virchow, a physician who had been studying how disease affects living things, reasoned that cells come only from other
cells. Over the years, modern scientists have gathered much additional evidence that strongly supports the cell theory.
6. The figure below indicates events that lead up to the cell theory. Draw and complete the table by filling in the blank spaces.CellTheoryTable.gif
7. The cell theory was
a. first identified in 1665.
b. the end result of many scientific investigations.
c. described by Rudolf Virchow.
d. Both (a) and (b)

Cells in Organisms
Some organisms are simple in that they only have one cell and others are more complex in that they have many cells. The one cell of single celled organisms must must do every life function. For example, the cell of an amoeba must be able to move, take in food, and eliminate wastes. The cells of multicellular organisms are usually more specialized in that different cells in them perform different functions. These differentiated and specialized cells often form tissues organs, and organ systems. A group of similar cells that carry out a specific function is called a tissue. Skin is a tissue. Groups of tissues that perform a particular job in an organism are called organs. An organ system is a group of organs that accomplish related tasks. The stomach and liver are organs that are part of the digestive system. Finally, several organ systems combine to make up an organism.

8. What is a tissue?
9. What is an organ?
10. What is an organ system?

11. Organ systems
a. are made up of a group of organs that work together.
b. interact together to carry out the processes of life.
c. work independently from each other.
d. Both (a) and (b)

Two Types of Cells

All living organisms are composed of one or more cells. Organisms grow mainly by increasing the number of their cells, rather than by increasing the size of their cells. Every cell must be able to enclose itself from the external environment. The barrier used to surround the cell is called the cell membrane. The thick liquid part of a cell inside the cell membrane is called cytoplasm. Besides cytoplasm and a cell membrane, all cells also contain hereditary material. Most cells have internal structures called organelles in their cytoplasm, which carry out specific functions for the cell. There are two types of cells - prokaryotic cells and eukaryotic cells. Bacteria consist of prokaryotic cells that lack organelles and a nucleus. Proteins and enzymes in the cytoplasm of prokaryotic cells carry out all the life processes. Eukaryotic cells have organelles and a nucleus. Organelles are membrane bound structures that can act as storage sites, process energy, move materials, or manufacture substances. Prokaryotic cells tend to be small while eukaryotic cells are bigger. In fact, some prokaryotic cells are similar in size to the organelles in eukaryotic cells. A network of supportive protein fibers called a cytoskeleton is also found in eukaryotic cells, but prokaryotic cells only hae a cell wall. The DNA of prokaryotic cells consists of a simple loop, whereas the complex DNA of eukaryotic cells can form structures called chromosomes and is wrapped around proteins called histones. These are some of the the similarities and differences between prokaryotic and eukaryotic cells.

12.
Draw two intersecting circles and make a Venn diagram showing the similarities and differences between prokaryotic and eukaryotic cells.
venn_diagram_blank.gif