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Topic 2
Cells
2.1.1 The Cell Theory
2.1.2 Evidence for the Cell Theory
Theories:
Theories are developed after the accumulation of
much data. Sometimes, theories are completely
abandoned because of conflicting evidence.
The formulation of the Cell Theory has taken several
hundred years of research and has amassed
tremendous credibility through use of the
microscope…the electron microscope (EM) has
allowed us to study the ultrastructures of cells.
Theories and Laws
2.1.1 The Cell Theory
2.1.2 Evidence for the Cell Theory
1. All organisms are composed of one or more
cells.
2. Cells are the smallest units of life and the basic
units of structure and function in living things.
3. All cells come from pre-existing cells.
The discovery of cells was linked to
developments in technology, in particular the
production of high quality lenses for
microscopes.
The Cell Theory
Discoveries Which Led to the Cell Theory
• 1590- Dutch optician, Zacharias Jansen, invents compound
microscope- 2 lenses for greater magnification
• 1665- Englishman, Robert Hooke, studies cork and names
the structures “cells”
• 1675- Dutchman, Anton van Leeuwenhoek, discovers
unicellular organisms
• 1838- German, Mathais Schleiden, suggests all plants are
made of cells
• 1839- German, Theodor Schwann, suggests all animals are
also made of cells
• 1840- Czech, Jan Evangelista Purkinje, names the cell
contents “protoplasm”
• 1855- German, Rudolf Virchow, suggests “all cells come from
cells”
• 1860s- Louis Pasteur sterilized chicken broth to disprove
“spontaneous generation”
Protoplasm
2.1.3 Functions of Life
1. Metabolism- all the chemical rxs that occur within an
organism
2. Growth- may be limited, but is always evident
3. Reproduction- heredity molecules passed to offspring
4. Response- to the environment is imperative to survival
5. Homeostasis- maintaining a constant internal
environment ex. T° or acid-base levels (pH)
6. Nutrition- source of compounds (food) with many
chemical bonds which can be broken to provide
energy and nutrients to maintain life
Characteristics of Cells
Viruses: Living or Non-Living?????
Viruses are not considered to be living. They
cannot carry out the functions of life on their
own (they have no metabolism). However,
they do utilize cells to perpetuate themselves.
Introduction to Viruses
2.1.4 Cells and Sizes
• Cells are made up of different subunits.
• These subunits are all microscopically small.
• Microscopes with high magnification and resolution
are needed to observe cells and their subunits.
• Cells are relatively large (100 µm), and then in
decreasing size order are:
learn this:
– organelles
10 µm
– bacteria
1 µm
– viruses
100 nm
– membranes 10 nm
– molecules
1 nm
meter
m
1
# in 1 m
millimeter
mm
10-3
1000
micrometer
µm
10-6
1000000
nanometer
nm
10-9
1000000000
Types of Microscopes
• Compound Light Microscopes- use light which is passed
through a specimen to form an image
• Can view living or dead specimens
• Magnification = 1000X (classroom = 400X)
– Eyepiece = 10X
– 3 objective lenses 4X, 10X and 40X
• Stains are often used to enhance viewing organelles
– Electron Microscopes- electrons (e-) pass through a
specimen to form an image
• Can only view dead specimens
SEM
• Magnification = > 100,000X
• SEM (scanning electron microscope) produces an image of the
surface of a cell or specimen
TEM
• TEM (transmission electron microscope) produces an
image of the interior of a cell or specimen
Electron Microscopes
TEM and SEM
Cells and Size
(these are typical sizes- there are exceptions)
STRUCTURE
Eukaryotic Cell (animal and plant)
(plant cells and egg cells are generally larger)
Prokaryotic Cell (bacteria)
SIZE
10 - 100 µm
1 - 5 µm
Nucleus
10 - 20 µm
Chloroplast
2 - 10 µm
Mitochrondion
0.5 - 5 µm
Bacteria (largest known = 1 mm)
1 - 5 µm
Large Virus (HIV)
100 nm
Ribosome
25 nm
Cell Membrane
DNA Double Helix
Hydrogen Atom
7.5 nm thick
2 nm diameter
0.1 nm
2.1.5 Calculating Magnification and
Actual Size of Micrograph Images
Magnification = size of image divided by
size of specimen
or
Magnification = magnified size (ruler)
real size (scale bar)
Light, TEM or SEM????????
Find the actual size of the specimen!!!
Magnification can be indicated next to a
diagram or a scale bar can be given.
3000X
1 mm
Find the size of
this vessicle in a
mouse kidney
cell.
1 mm
Remember magnification = size of image/size of specimen
(measure this)
So, 3000= 12 mm/x
now solve for x
x= 12 mm/3000 = .004 mm or 4.00 µm
(actual size)
Using the Field of View to
Determine the Size of a Specimen