Chapter 3:
Cells and
cell structure
Cells
• A cell is the smallest unit of life.
• Each cell is alive and has all of the
characteristics of life.
• Cytology is the study of cells.
• Scientists began learning about
cells after the development of the
microscope
Robert Hooke - 1665
Hooke was the 1st person to see cells. Hooke coined the
word “cell” after viewing cork cells with a microscope
Late 1600s
Leeuwenhoek’s microscope
Anton von Leeuwenhoek
Was the 1st to observe living
cells. He saw unicellular living
organisms (“wee beasties”)
and other living cells.
What did Leeuwenhoek see?
Algae
Vorticella,
a protist
Bacteria
Schleiden & Schwann
• Mattias Schleiden
observed that all
plants were made up
of cells.
• Theodor Schwann
observed that all
animals were made
up of cells.
The Cell Theory
• All living things are made of one
or more cells.
• Cells are the basic building
blocks of organisms.
• All cells come from from existing
cells by the process of cell
reproduction.
Virchow
History of Cells 5 min
All cells come from preexisting cells
Microscopes
have:
Magnification
Resolution
making an
a measure of
image appear the clarity of
larger
an image
Microscopes
1. Compound Light Microscope
2. Transmission Electron
Microscope (TEM)
3. Scanning Electron Microscope
(SEM)
Compound Light Microscope
Up to about 1000x
Elodea leaf at 40x
Elodea leaf at 400x
Answer this!
A student wants to view cells
under the compound microscope
at a total magnification of 400X. If
the eyepiece is 10X, which
objective lens should be used?
Transmission Electron
Microscope (TEM)
Highly magnified, 2-dimensional images
Plant cell
Transmission electron
micrograph
Liver cell
more Transmission Electron
Micrographs
A mitochondrion
A nucleus in a cell
Even more TEMs
Endoplasmic reticulum
Golgi apparatus
Scanning Electron
Microscope (SEM)
3-dimensional images
Tsetse fly head
Scanning Electron Micrographs
Human hair in a knot
Human hair
with dandruff
More SEMs
Human hair with split ends
Human hair emerging
from skin
More SEMs
Dog tongue
More SEMs
A daphnia (water flea)
More SEMs
Scotch tape
More SEMs
Paper towel
Why are cells so small?
All substances must pass
through the cell membrane.
Thus, the surface area of the
cell membrane must be
sufficient for the volume of a
cell.
All Cells Have:
1) Cell membrane - the outer boundary. It
separates the inside from the outside & controls
what enters & leaves the cell.
2) Cytoplasm – everything inside the cell except
for the nucleus.
3) Ribosomes - the place on which proteins are
made
4) Genetic material (DNA) - instructions for the
cell. In eukaryotes, it is kept in the nucleus. It is
often called the “brain” of the cell.
Types of Cells
Pro & Euk 1 min
Prokaryotes vs Eukaryotes
• Prokaryotes are single cells that lack a
true nucleus. Prokaryotes are bacteria.
• Eukaryotes are cells that have a true
nucleus and membrane-bound internal
organelles.
• An organelle is a structure surrounded by
a membrane, found only in eukaryotic
cells.
Relative Sizes of Prokaryotes
and Eukaryotes
Prokaryotes are Bacteria
• Bacteria are found in all environments on
earth.
• Bacteria are hypothesized to have been
the first life on earth. The first bacteria
“ate” organic molecules. Later, bacteria
evolved that could do photosynthesis,
getting energy from the sun. Oxygen was
released into the atmosphere and other
cells could develop, and eventually multicellular organisms appeared.
Prokaryote Video 2 min
Archaebacteria
Many are
Extremophiles,
living in extreme
environments
such as hot springs
and acid pools.
Eubacteria, common bacteria
E. coli are
found in
your
intestines
Bacterial Cell
Structure of a Prokaryote:
• Cell wall – provides structure &
protection.
• Pili – helps bacteria stick to
surfaces
• Flagella – allows bacteria to move
Yet another bacterial cell
Bacillus: Rod-shaped
bacteria
Coccus: Round-shaped
Bacteria
Spirilla: Spiral-shaped
Bacteria
Many bacteria are beneficial
• Food
• Some antibiotics
• Decomposers (saprobes)
• Nitrogen fixation – converts nitrogen gas in
the air to a form that plants can use.
• Photosynthesis (cyanobacteria)
• Environmental cleanup
Cyanobacteria:
Photosynthetic bacteria
Bacteria that caused bubonic
plague
Y. pestis
Some bacteria are pathogens
Pathogen: a diseasecausing agent
Pathogenic Bacteria
Bacteria that are pathogenic secrete
a toxin (poison)
Antibiotic – a chemical that kills
bacteria
Bacteria that cause anthrax
Bacteria that cause botulism
Some other bacterial diseases
Cholera
Dental cavities
Lyme disease
Tuberculosis
Typhus
Strep throat
Botulism (a type of food poisoning)
A Eukaryote
Eukaryotes
• All cells except bacteria are eukaryotic.
• Early bacteria released oxygen into the air
through photosynthesis. Oxygen is
necessary for eukaryotic cells to make
energy. So, eukaryotic cells could
develop. This is called the “oxygen
revolution”.
Eukaryotic Animal Cell
Eukaryotic Plant Cell
Cell Membrane: controls what
enters & leaves the cell
Plasma (cell) Membrane
Cell Wall
•Found only in plant cells
•Gives plant cells structure
•Makes up the bark of trees
Cell Wall Video 35 sec
Nucleus
Contains DNA, so the nucleus is
called the “brain” of the cell. It
controls all cell activities.
Nucleus
DNA
Nucleolus & Ribosomes
• Nucleolus is found within the nucleus.
• It makes ribosomes, which will then leave
the nucleus and go into the cytoplasm.
• Ribosomes: the place where proteins are
made.
Endoplasmic Reticulum
Endoplasmic Reticulum (ER)
•Passageways in the cell for transportation
of molecules
•Rough ER has ribosomes
•Smooth ER does not have ribosomes
ER 1 min
Golgi Apparatus
Golgi apparatus
•Repackages proteins and lipids.
•It exports molecules through structures
called vesicles.
Lysozomes
Lysosomes
•Digestion of worn-out cell parts
•The lysosomes contain digestive enzymes.
Mitochondria
Mitochondria
• The “mighty mitochondria” provides energy
for the cell.
• It is referred to as the “powerhouse” of the
cell.
The mitochondria is folded!
• The mitochondrion has an inner
membrane and an outer membrane.
The inner membrane has many folds.
Energy (ATP) is made along these folds.
• The folds allow for high surface area,
which means that a lot of energy can
be made in a small space.
Chloroplast
• This green structure is found only in plant cells.
• Photosynthesis occurs here.
• Photosynthesis is the process by which plants
use carbon dioxide and water to make
glucose (sugar) and oxygen.
Chloroplasts
Cytoskeleton
A series of protein fibers and microtubules
that provide structure and movement of
organelles inside of the cell.
Cilia and flagella are structures that help a
cell to move.
Cilia
Flagella
Cilia & Flagella 40 sec
Plant vs Animal Cells
• All cells (prokaryotic & eukaryotic) have 4
structures in common – remember them?
• Plant and animal cells are both eukaryotic
cells.
• Some animal cells have cilia and flagella.
• Plant cells have:
– chloroplasts (for photosynthesis)
– cell wall
– large central vacuole
Organization of Organisms
Organization of Cells in a Multicellular
Organism
• Multicellular: made up of many cells
• Multicellular organisms can be large because
cells specialize and do different functions.
• Specialized cell: a cell programmed by its
DNA to perform one primary job for the
organism.
Organization of Cells in a Multicellular
Organism
• Cell
• Tissue – a group of cells with similar
structure & function.
• Organ – a group of tissues which have
formed a specialized structure with a specific
function.
• Organ system – group of organs which
carry out a major body function
• Organism