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Chapter 7
A View of the Cell
Cell Theory
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• Before microscopes, people thought
diseases were caused by curses and
supernatural spirits
– They had no idea microorganisms, such as
bacteria and viruses existed
• When the microscope was invented,
scientists discovered cells exist
• Cells are the basic units of living
organisms
Cell Theory
• Anton van Leeuwenhoek (Dutch) used the
first simple light microscope in the 1600s
– It had one lens (page 1064)
• Gradually, lenses got better
• Compound light microscopes use a series
of lenses to magnify objects in steps
– Can magnify up to 1500 times
– The microscopes we use in the lab
Cell Theory
• Robert Hooke (1600s, English) used a
compound light microscope to study cork,
the dead cells of oak bark
• He saw small, geometric shapes that
reminded him of the small rooms monks
lived in called cells
• Cells are the basic units of all living things
Cell Theory
• Matthias Schleiden (1830s, German)
discovered that all plants are made of cells
• Theodor Schwann (German) discovered
that all animals are made of cells
• Rudolf Virchow discovered that all cells
come from existing cells
• All these scientists (plus others)
contributed ideas that are now summed up
in what we call the cell theory
Cell Theory
1. All organisms are composed of one or
more cells.
2. The cell is the basic unit of structure and
organization of organisms.
3. All cells come from preexisting cells.
Electron
Microscopes
• Electron Microscopes
let us see a much
greater magnification
than light microscopes
– They use beams of
electrons to
produce images
• Scanning Electron
Microscope
– Used for scanning
3-D surfaces
Electron
Microscopes
• Transmission
Electron
Microscope
– Used for
scanning
interior
structures of
cell
Types of Cells
• Organelles are small, specialized
structures within cells
– Many, but not all are surrounded
by membranes
• Prokaryotes are organisms that do
not have membrane-bound
organelles (biology.arizona.edu)
– Kingdom Monera ( now split into
Eubacteria & Archaebacteria)
• Eukaryotes are organisms that do
have membrane-bound organelles
– Kingdoms Animalae, Plantae,
Fungi, Protista
Types of Cells
• Robert Brown (Scottish) observed that
eukaryotic cells have a prominent
structure, the nucleus
– the nucleus manages cellular functions
• Rudolf Virchow concluded that this
prominent structure was responsible for
cell division
Section 1 Review
1. How has the history of microscopes
influence the study of cells?
2. What are the three parts of the cell
theory?
3. What is the difference between a light
microscope and an electron microscope?
4. What is the difference between a
prokaryote and a eukaryote?
The Plasma Membrane
• Cells must maintain proper conditions within
itself to function
• The plasma membrane is a flexible boundary
between the cell and its environment
– It allows a steady supply of nutrients into and out of
the cell at the appropriate levels
• The plasma membrane is selectively permeable
– This means that it allows some molecules to pass
through while keeping others out.
– Like a screen in a window
The Plasma Membrane
• Phospholipids
• The “head” is polar, or slightly charged
– It is hydrophilic (likes water)
• The “tail” is nonpolar, or not charged
– It is hydrophobic (repels water)
• The phospholipids arrange themselves form a
bi-layer with the fatty acid
tails forming the interior
and the heads facing the
watery environments
outside and inside the cell
Plasma Membrane
• The plasma membrane is called a phospholipid
bilayer
• Arranged in this manner, a barrier is created that
is water-soluble at its outer surfaces and waterinsoluble in the middle
• Keeps out both
water soluble
and water
insoluble
molecules
Plasma Membrane
• The current model of the plasma
membrane is called the fluid mosaic
model.
• The phospholipids actually move around
like a fluid.
• The other components of the membrane
(proteins, carbohydrates, cholesterol, etc.)
move around as well
Plasma Membrane
• Cholesterol helps to stabilize the phospholipids
by preventing their fatty acid tails from sticking
together
• Transport proteins move span the membrane
and move needed substances or waste
materials through the plasma membrane
• Other proteins and carbohydrates that stick out
help cells to identify surface signals and other
cells
– These proteins play an important part in protecting
cells from infection
Section 2 Review
1.
2.
3.
4.
What is a phospholipid?
Why is the cell membrane a bilayer?
What does polar and nonpolar mean?
What are the specialized parts of the cell
membrane?
5. Why is the cell membrane referred to as
fluid mosaic?
Cell Wall
• Fairly rigid structure located
outside the plasma
membrane of some cells
that provides additional
support and protection
– Plants, fungus, most bacteria
• The cell wall is very
porous, made of a
tough mesh of fibers
– Like framing of a house
Nucleus
• Membrane-bound (called
nuclear envelope) organelle
that contains the directions to
make proteins
• Nuclear pores allow passage
through the nuclear envelope
• Chromatin - uncondensed
strands of DNA
– When cell is dividing, DNA
condenses into
chromosomes
• Nucleolus - organelle within
the nucleus that make
ribosomes
Organelles
• Ribosomes are the sites where
the cell produces proteins
according to the directions of
DNA
– One organelle without a
membrane
• Cytoplasm is the clear,
gelatinous fluid inside the cell
– Acts as a medium for things
to move around in the cell
– “Organelles can’t fly”
Organelles
• The endoplasmic reticulum (ER) is
arranged in a series of highly
folded membranes suspended in
the cytoplasm
• In general, ER is involved in the
movement of materials throughout
the cell
• Rough ER has ribosomes, which is
where protein synthesis takes
place
• Smooth ER has no ribosomes and
is involved in numberous
biochemical activities, including the
production and storage of lipids
Organelles
• The Golgi apparatus is a
flattened stack of tubular
membranes that modifies
the proteins
• The Golgi sorts proteins
into packages and packs
them into membranebound structures called
vescicles for later
transport (like UPS)
Organelles
• Vacuoles are
membrane-bound
compartments for
temporary storage
of materials
– Store food,
enzymes, water,
waste
– Plant cells have one
very large vacuole
Organelles
• Lysosomes are organelles
that contain digestive
enzymes
• Digest old organelles,
food, viruses, bacteria, etc.
• Can fuse with a vacuole to
dump waste or give
enzymes
• Lysosomes digest a
tadpole’s tail
Organelles
• Plastids are a group of
organelles used for storage
– Named for the color or
pigment they contain
• Chloroplasts are organelles
that capture light energy
and convert it to chemical
energy (photosynthesis
occurs here)
– Plastid containing chlorophyll,
which actually traps the light
and gives plants green color
Organelles
• Mitochondria are
membrane-bound
organelles in plant and
animal cells that transform
stored chemical energy
into a usable form for the
cell (ATP)
• Has an outer and inner
highly folded membrane
– ATP produced on inner folds
Organelles
• The cytoskeleton forms a framework for the
cell
– A network of tiny rods and filaments
• Cytoskeleton is constantly changing its shape
• Microtubules are thin, hollow cylinders made of
protein
• Microfilaments are smaller, solid protein fibers
• Give support for cell
• Provide “highway system” for organelles to
move throughout cell
Organelles
• Centrioles are organelles made up
of microtubules that play a part in
cell division
– In animals and most protists
• Cilia are short, numberous
projections that look like hairs
– Made of microtubules and help
organelles move and feed
• Flagella are longer projections that
move in a whip-like motion
– Made of microtublules - help
with movement
– Cells usually only have 1 or 2
Animal Cell
Plant Cell
Section 3 Review
1.
2.
3.
4.
5.
6.
7.
How are highly-folded membranes an advantage for
the functions of cellular parts?
Name an organelle that has highly-folded membranes.
If a cell synthesizes large quantities of protein
molecules, which organelles might be numerous in that
cell?
A cell’s digestive enzymes are enclosed in a
membrane-bound organelle. How can these
molecules function in the cell?
Compare and contrast the functions of a cell wall to the
functions of a plasma membrane.
What are the functions of the cytoskeleton?
Why are mitochondria and chloroplasts referred to as
energy transporters?