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Cells: An Introduction

Developing Ideas About Life In the 1600s, Dutch businessman Anton van Leeuwenhoek became one of the first people to use a microscope to study nature. Using only a single powerful lens, van Leeuwenhoek crafted instruments that could produce magnified images of very small objects. His simple microscope enabled him to see things that no one had ever seen before. He was the first person, for example, to see tiny living organisms in a drop of water. Van Leeuwenhoek carefully observed the living things in pond water and made detailed drawings of each kind of organism.

In 1665, English physicist Robert Hooke used one of the first light microscopes to look at thin slices of plant tissues. One of these, a slice of cork, especially caught his eye. Under the microscope, cork seemed to be made of thousands of tiny chambers. Hooke called these chambers “cells,” because they reminded him of a monastery’s tiny rooms, which were also known as cells. The term cell is used to this day. Hooke’s discovery stimulated other scientists to search for cells in other living things. Before long, it became apparent that cells were the basic unit of all forms of life.

During the years 1838-1839, German botanist Matthias Schleiden concluded that all plants are made of cells, while another German scientist, Theodor Schwann, concluded that all animals are also made of cells. In 1855, Rudolf Virchow, a German physician, studied cell reproduction and concluded cells could only come from other cells. The discoveries of these scientists, as well as others, have developed into a basic concept of biological thought known as the cell theory. The Cell Theory states: 1) All living things are composed of cells; 2) Cells are the basic unit of structure & function for all living things; 3) All cells arise from preexisting cells.

Basic Unit of Life The body of a living organism is built of units called cells. All living things are similar in that they are composed of one or more cells. Each living thing begins life as a single cell. The body of a unicellular organism is composed of one cell. Protists are single celled organisms. Most plants and animals are multicellular, having a body made of numerous cells. In multicellular organisms, the original cell grows to a certain size and then divides. Unlike unicellular organisms, the cells of multicellular plants and animals hold together forming tissues. Tissues than form organs, and organ systems, and finally the complete organism. As the number of cells increases in the body of a plant or animal, so does its size. Large organisms have more cells than smaller organisms. There are two main categories of organisms: Prokaryotes, which do not have nuclei, and consist of bacteria; Eukaryotes, which do have nuclei, and consist of all other plants, animals, etc. except bacteria.

Basic Unit of Structure & Function Microscopic examination of plant and animal parts indicates that the bodies of living organisms are composed of cells. Cells provide structure and form to the body. They appear in a variety of shapes: round, concave, rectangular, elongate, tapered, spherical and others. Cell shape seems to be related to specialized function. Cells not only vary in shape, but they also differ in size. Most plant and animal cells are quite small, ranging in size between 5 and 50 micrometers (.001 mm) in diameter. Each cell is a living unit. Whether living independently as a protist or confined in a tissue, a cell performs many metabolic functions to sustain life. Each cell is a biochemical factory using food molecules for energy, repair of tissues, growth and ultimately, reproduction. On the chemical level, the cell carries out all of the life functions. Living organisms function the way they do because their cells have the properties of life.

New Cells from Preexisting Cells New cells arise only from preexisting cells. A cell grows to optimum size and then divides, producing two other cells identical to itself. Paramecia produce other paramecia; onion membrane cells produce new onion membrane cells identical in structure and function to themselves. From single cells, multicellular organisms produce other organisms like themselves. This is so because cells carry hereditary information from one generation to the next.

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Graphic Organizer—Cells: An Introduction

What did Anton van Leeuwenhoek do? What did Robert Hooke do?

What was the conclusion of Matthias Schleiden?

What was the conclusion of Theodor Schwann?

What was the conclusion of Rudolf Virchow?

What are the parts of the Cell Theory? 1. 2. 3.

Define Unicellular: Define Multicellular:

Example of Unicellular organisms: Example of Multicellular organisms:

Define Prokaryote: Define Eukaryote:

Example of Prokaryote organism: Example of Eukaryote organism: