Download Chapter 7 Section 7_1 Life is Cellular

Chapter 7: Cell Structure and Function
7.1 – Life is Cellular
Mr. M. Varco
Saint Joseph High School
The Discovery of the Cell
•What is the smallest part of any living thing that counts as being “alive”?
•The cell is the smallest unit of any organism, and are considered to be
the basic unit of life.
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The Discovery of the Cell
Early Microscopes:
•In 1665, Englishman Robert Hooke used an early compound microscope
to observe thin slices of cork
•Hooke observed thousands of tiny empty chambers,
which he referred to as “cells”
•Today, we know cells are not empty chambers,
but rather composed of multiple working parts
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The Discovery of the Cell
Monastery Chambers
Cells in a Cork Sample
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The Discovery of the Cell
Early Microscopes:
•In Holland, Anton van Leeuwenhoek used a microscope to observe
pond water and other things
•Observed tiny living organisms everywhere he looked
– Pond water, drinking water, neighbor’s mouth
•These organisms today are called bacteria
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The Discovery of the Cell
•
These scientist’s observations concluded that the basic unit of life
are Cells
•
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1838: Matthias Schlieden concluded all plants are made of cells
1839: Theodor Schwann concluded all animals are made of cells
•
In 1855, Rudolf Virchow concluded new cells can only be produced
by division of existing cells
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The Discovery of the Cell
The Cell Theory:
– All living things are made up of cells
– Cells are the basic unit of structure and function in living things
– New cells are produced from existing cells
•The Cell Theory was initially supported by observation; later by
experimentation
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Exploring the Cell
Microscopes:
•Most microscopes use lenses to magnify the image of an object by
focusing light or electrons
•Two types of microscopes are particularly important:
– Light Microscope
– Electron Microscope
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Exploring the Cell
Light Microscopes
•Light microscope allows light to pass through specimens
•Relies on the use of two types of lenses:
– Objective Lens: Enlarges image of specimen
– Ocular Lens: Magnifies image further
•Limitations of light microscopes include:
– Light waves are diffracted when passing through image (limit 1000x)
– Most living cells are transparent, making observation of structure
difficult
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Exploring the Cell
Light Microscopes
•Observation of transparent cells relies on a process called Cell Staining
•Cell staining used to reveal specific structure within the cells
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Exploring the Cell
Electron Microscopes (EM)
•These microscopes are used to observe objects as small as 1 billionth
of a meter (viruses, cellular structures)
•Relies on a beam of electrons focused by magnetic fields, rather
than light
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Exploring the Cell
2 Types of EM:
•Transmission electron microscope (TEM):
– Images produced are often flat, two-dimensional
•Scanning electron microscope (SEM):
– Images produce are often three-dimensional images
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Exploring the Cell
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Cell Characteristics
•
Cells range in size from 5 to 50 micrometers in length
•
Despite differences in their size, all cells share common traits:
– All cells contain DNA at some point
– All cells are surrounded by a thin, flexible barrier called a cell membrane
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Prokaryotes and Eukaryotes
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Cells fall into two broad categories, depending on the presence of a
nucleus
•
A nucleus is a large membrane-enclosed structure that contains
genetic material in the form of DNA
– Controls many of the cell’s activities
•
There are two categories of cells: prokaryotes and eukaryotes
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Prokaryotes and Eukaryotes
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Cells that lack a nucleus and therefore do not enclose their DNA in
nuclei are prokaryotes
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Cells that enclose their DNA in a nuclei are called eukaryotes
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Prokaryotes and Eukaryotes
Prokaryotes
•Cells that do not separate their genetic material within a nucleus
•Prokaryotes are generally smaller and simpler than eukaryotic cells,
though they grow, reproduce, and respond to the environment
•Example of prokaryotes are Bacteria
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Prokaryotes and Eukaryotes
Eukaryotes
•Cells that separate their genetic material within a nucleus
•Eukaryotes are generally larger and more complex than prokaryotes,
and contain highly specialized internal structures
•Examples include animal cells and plant cells
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