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Biology
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7-1 Life Is Cellular
Photo Credit: © Quest/Science Photo Library/Photo Researchers, Inc.
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3. The Discovery of the Cell
Because there were no instruments to make cells visible, the existence of cells was unknown for most of human history.
This changed with the invention of the microscope.
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4. The Discovery of the Cell
Early Microscopes
In 1665, Robert Hooke used an early compound microscope to look at a thin slice of cork, a plant material.
Cork looked like thousands of tiny, empty chambers.
Hooke called these chambers “cells.”
Cells are the basic units of life.
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5. The Discovery of the Cell
Hooke’s Drawing of Cork Cells
hoto Credit: © Peter Arnold, Inc.
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6. The Discovery of the Cell
At the same time, Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things.
The microscope revealed a world of tiny living organisms.
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7. The Discovery of the Cell
What is the cell theory?
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8. The Discovery of the Cell
The Cell Theory
In 1838, Matthias Schleiden concluded that all plants were made of cells.
In 1839, Theodor Schwann stated that all animals were made of cells.
In 1855, Rudolph Virchow concluded that new cells were created only from division of existing cells.
These discoveries led to the cell theory.
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9. The Discovery of the Cell
The cell theory states:
All living things are composed of cells.
Cells are the basic units of structure and function in living things.
New cells are produced from existing cells.
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Exploring the Cell
Exploring the Cell
New technologies allow researchers to study the structure and movement of living cells in great detail.
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Exploring the Cell
Electron Microscopes
Electron microscopes reveal details 1000 times smaller than those visible in light microscopes.
Electron microscopy can be used to visualize only nonliving, preserved cells and tissues.
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Exploring the Cell
Transmission electron microscopes (TEMs)
Used to study cell structures and large protein molecules
Specimens must be cut into ultra-thin slices
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Exploring the Cell
Scanning electron microscopes (SEMs)
Produce three-dimensional images of cells
Specimens do not have to be cut into thin slices
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Exploring the Cell
Scanning Electron Micrograph of Neurons
Photo Credit: © Dr. Dennis Kunkel/Phototake
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Exploring the Cell
Confocal Light Microscopes
Confocal light microscopes scan cells with a laser beam.
This makes it possible to build three-dimensional images of cells and their parts.
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Exploring the Cell
Confocal Light Micrograph of HeLa Cells
Photo Credit: © K.G.Murti/Visuals Unlimited
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Exploring the Cell
Scanning Probe Microscopes
Scanning probe microscopes allow us to observe single atoms.
Images are produced by tracing surfaces of samples with a fine probe.
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Exploring the Cell
Scanning Probe Micrograph of DNA
Photo Credit: Dr. Jan Hoh of Johns Hopkins University, School of Medicine
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19. Prokaryotes and Eukaryotes
Cells come in a variety of shapes and sizes.
All cells:
are surrounded by a barrier called a cell membrane.
at some point contain DNA.
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20. Prokaryotes and Eukaryotes
Cells are classified into two categories, depending on whether they contain a nucleus.
The nucleus is a large membrane-enclosed structure that contains the cell's genetic material in the form of DNA.
The nucleus controls many of the cell's activities.
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21. Prokaryotes and Eukaryotes
Eukaryotes are cells that contain nuclei.
Prokaryotes are cells that do not contain nuclei.
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22. Prokaryotes and Eukaryotes
What are the characteristics of prokaryotes and eukaryotes?
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23. Prokaryotes and Eukaryotes
Prokaryotic cells have genetic material that is not contained in a nucleus.
Prokaryotes do not have membrane-bound organelles.
Prokaryotic cells are generally smaller and simpler than eukaryotic cells.
Bacteria are prokaryotes.
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24. (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral 1 µm 2 µm
Fig. 27-2
Figure 27.2 The most common shapes of prokaryotes
1 µm
2 µm
5 µm
(a) Spherical
(cocci)
(b) Rod-shaped
(bacilli)
(c) Spiral

25. Prokaryotic cells have much less DNA than the eukaryotic cells
Most of the DNA consists of a circular chromosome
Some species of bacteria also have smaller rings of DNA called plasmids

26. Nitrogen-fixing prokaryotes add usable nitrogen to the environment
Chemical Cycling
Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems
Many prokaryotes function as decomposers, breaking down corpses, dead vegetation, and waste products
Nitrogen-fixing prokaryotes add usable nitrogen to the environment

27. (b) (c) (a) Fig. 27-22 Figure 27.22 Some applications of prokaryotes
For the Discovery Video Tasty Bacteria, go to Animation and Video Files.

28. Pathogenic Prokaryotes
Prokaryotes cause about half of all human diseases
Lyme disease is an example

29. 5 µm Fig. 27-21 Figure 27.21 Lyme disease
For the Discovery Video Antibiotics, go to Animation and Video Files.

30. Prokaryotes and Eukaryotes
Eukaryotic cells contain a nucleus in which their genetic material is separated from the rest of the cell.
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31. Prokaryotes and Eukaryotes
Eukaryotic cells are generally larger and more complex than prokaryotic cells.
Eukaryotic cells generally contain dozens of structures and internal membranes.
Many eukaryotic cells are highly specialized.
Plants, animals, fungi, and protists are eukaryotes.
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7-1
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7-1
The cell theory states that new cells are produced from
nonliving material.
existing cells.
cytoplasm.
animals.
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7-1
The person who first used the term cell was
Matthias Schleiden.
Lynn Margulis.
Anton van Leeuwenhoek.
Robert Hooke.
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7-1
Electron microscopes are capable of revealing more details than light microscopes because
electron microscopes can be used with live organisms.
light microscopes cannot be used to examine thin tissues.
the wavelengths of electrons are longer than those of light.
the wavelengths of electrons are shorter than those of light.
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7-1
Which organism listed is a prokaryote?
protist
bacterium
fungus
plant
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7-1
One way prokaryotes differ from eukaryotes is that they
contain DNA, which carries biological information.
have a surrounding barrier called a cell membrane.
do not have a membrane separating DNA from the rest of the cell.
are usually larger and more complex.
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38. END OF SECTION