Transcript Biology - Midland Park School District

Chapter 7: Cell Structure
and Function
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7.1 Life is Cellular
Objectives
•State the cell theory
•Describe how different
types of microscopes work
•Distinguish between
prokaryotes and eukaryotes
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7-1 Life Is Cellular
The Discovery of the Cell
The Discovery of the Cell
The invention of the microscope led to the
discovery of the cell.
Jansenn’s
microscope, 1595
Leeuwenhoek’s
microscope, 1673
Hooke’s
microscope, 1670
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7-1 Life Is Cellular
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. It seemed to be made up of thousands of
tiny, empty chambers.
Hooke called these chambers “cells.”
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7-1 Life Is Cellular
The Discovery of the Cell
At the same time, Anton van Leeuwenhoek used
a single-lens microscope to observe pond water
and other things, including a sample taken from a
human mouth.
The microscope revealed a world of tiny living
organisms.
Bacteria in mouth
Pond water
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7-1 Life Is Cellular
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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7-1 Life Is Cellular
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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7-1 Life Is Cellular
Life Is Cellular
Lesson Overview
Exploring the Cell
Most microscopes use lenses to
magnify the image of an object by
focusing light or electrons.
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7-1 Life Is Cellular
Life Is Cellular
Lesson Overview
Light Microscopes and Cell Stains
A typical light microscope allows light to pass
through a specimen and uses two lenses to form an
image. The first set of lenses, located just above the
specimen, produces an enlarged image of the
specimen. The second set of lenses magnifies this
image still further.
Because light waves are diffracted, or scattered, as
they pass through matter, light microscopes can
produce clear images of objects only to a
magnification of about 1000 times.
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7-1 Life Is Cellular
Life Is Cellular
Lesson Overview
Light Microscopes and Cell Stains
Another problem with light microscopy is that most
living cells are nearly transparent, making it
difficult to see the structures within them.
Using chemical stains or dyes can usually solve
this problem. Some of these stains are so specific
that they reveal only compounds or structures
within the cell.
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7-1 Life Is Cellular
Life Is Cellular
Lesson Overview
Light Microscopes and Cell Stains
Some dyes give off light of a particular color when
viewed under specific wavelengths of light, a
property called fluorescence.
Fluorescent dyes can be attached to specific
molecules and they can then be made visible using a
special fluorescence microscope.
Fluorescence microscopy makes it possible to see
and identify the locations of these molecules, and
even to watch them move about in a living cell.
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7-1 Life Is Cellular
Exploring the Cell
Electron Microscopes
Electron microscopes reveal details 1000 times
smaller than those visible in light microscopes.
Electron microscopes use beams of electrons, not
light, that are focused by magnetic fields.
Electron microscopy can be used to visualize only
nonliving, preserved cells and tissues.
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7-1 Life Is Cellular
Exploring the Cell
Transmission electron microscopes (TEMs)
• Specimens must be cut into ultra-thin slices
because electrons must pass through it.
• TEMs are used to study cell structures and large
protein molecules. Flat, two-dimensional images
are produced.
TEM image of an
ebola virus
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7-1 Life Is Cellular
Exploring the Cell
Scanning electron microscopes (SEMs)
• Beams of electrons scan over the surface of
specimens.
• SEMs produce three-dimensional images of a
specimen’s surface.
SEM image of a neuron
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7-1 Life Is Cellular
Prokaryotes and Eukaryotes
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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7-1 Life Is Cellular
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.
nucleus
cell membrane
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7-1 Life Is Cellular
Prokaryotes and Eukaryotes
Eukaryotes are cells
that enclose their DNA
in nuclei.
Prokaryotes are cells
that do not enclose
DNA in nuclei.
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7-1 Life Is Cellular
Prokaryotes and Eukaryotes
Prokaryotes
Prokaryotic cells have genetic material
that is not contained in a nucleus.
Prokaryotes do not have any membranebound organelles.
Prokaryotic cells are generally smaller and
simpler than eukaryotic cells.
Bacteria are prokaryotes.
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7-1 Life Is Cellular
Prokaryotes and Eukaryotes
Eukaryotes
Eukaryotic cells contain a nucleus in
which their genetic material is separated
from the rest of the cell.
Eukaryotic cells are generally larger and
more complex than prokaryotic cells.
Eukaryotic cells generally contain dozens of
structures and internal membranes.
Plants, animals, fungi, and protists are
eukaryotes.
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