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Cell Structure and Function
Ch. 4
A Look at Cells
• Cells are the smallest unit
of life that can carry out all
the functions of a living
thing. They are very
specialized.
• Living things are
unicellular or multicellular.
• They vary greatly in
shape.
• They vary greatly in
size.
– Bacteria  Ostrich
Egg
All Cells have 3 common features
1. Plasma membrane that separates each cell from
environment, permits flow of molecules across
membrane, and contains receptors that affect cells
activities.
2. Nucleus or nucleoid region that localized herditary
material, that is copy and read.
3. Cytoplam contains membrane system, particles,
filaments, and semifluid substance.
1.12 Prokaryotes vs. Eukaryotes
• Prokaryotes
– No nucleus
– No membrane bound
organelles
– Bacteria
– Much smaller
– Unicellular
– Some have cilia (hair-like
structures) and some
flagella (whip-like tail) for
movement.
Amoeba
• Eukaryotes
– Nucleus
– Organelles
– Unicellular (protists)
and multicellular
(animal and plants)
Plant Cell
Diffusion and DNA limit cell size
because…
• Cells rely on diffusion
to carry on proper
functions
– Cells require a constant
supply of glucose and
oxygen
– Cells must constantly
get rid of waste.
• DNA is found in all
cells.
– The larger the cell, the
greater number of
enzymes
– DNA makes enzymes
needed for the cell
Is bigger better?
• Surface Area to
Volume Ratio
– As the cell size
increases, its volume
increases 2x
faster….why is this a
problem?
Other ways to solve
the problem
• If cell size doubled, it
would be an 8 fold
increase in volume, but
the surface area would
only increase 4 fold.
Therefore, there is not
enough membrane for
nutrients to flow through
to keep the cell alive.
Who discovered cells and what
did they see?
• The invention of the
microscope was the key to
discovering cells.
• Robert Hooke looked at cork
cells. (1665)
• He thought they looked like
“jail cells” and that is why he
named them cells.
• In the early 1670’s
Leeuwenhoek made
microscopes that magnified
up to 200x and was the first
person to see living cells.
Other Cell Discoveries
• About 150 years later
Matthias Schleiden
discovered all plants
are made up of cells.
• At about the same
time Theodore
Schwann proposed
that all living things
are made up of cells.
• There are cells called
“Schwann Cells”.
The Cell Theory
• In 1858, Rudolf
Virchow proposed that
plant cells only arise
from existing plant
cells and new animal
cells only come from
other animal cells.
• The Cell Theory was
soon introduced.
• 3 principles:
1. Cells are the basic
units of all life.
2. All organisms are
made up of one or
more cells.
3. All cells arise from
other cells.
Types of Electron Microscopes used
to see cells
• Scanning Electron
Microscope (SEM)– Bounces e- off
specimen
– Creates 3-D image
– Magnifies up to
60,000x
• Transmission Electron
Microscope (TEM)
– E- pass through
– Specimens must be
very thin
– Magnifies up to
2,000,000x
Basic Cell Structures
• Cell Membrane
surrounds all of the
structures inside. It is
made up of a
phospholipid bilayer.
• Fluid Mosaic Model.
• Lipids are made up of
a glycerol, 2 fatty acid
chains, and a
phosphate group.
Cytoplasm
The Lipid Bilayer
• Hydrophobic tails (the
fatty acids)
• Hydrophilic heads (the
phosphate group)
• Proteins are embedded
in the lipid bilayer and
they allow certain
things to pass through
and other not.
1.2a All cells are covered by a membrane that controls what
enters and leaves the cell. This membrane is made up of a
complex network of proteins that provide organization and
shape. (In primitive cells, this is not the case).
• Hydrophobic tails.
• Hydrophilic heads.
• Proteins are embedded
in the membrane and
allow certain things to
pass and others not to.
Proteins in bilayer
• 1. receptors for chemical signals
• 2. transport solutes across bilayer
• 3. participate in cell identification, defense
and communication.
1.3a In cells, there are specialized parts called organelles
“little organs” used for the transport of materials, energy
capture and release, protein building, waste disposal,
information feedback, and movement.
• Endoplasmic
Reticulum
• Golgi Body
• Mitochondria
• Lysosomes
• Vacuoles
• 1.3b In most
multicellular
organisms, these
organelles perform
some special
functions that others
do not.
Cytoplasm
• The semifluid substance made
primarily of water and organic
compounds.
• Organelles and contained with
in the cytoplasm.
• Within the cytoplasm is a
cytoskeleton made up of
proteins and fibers. It gives the
cell support and shape.
The Nucleus
• It contains most of the cells
genetic material that codes
for instructions for making
proteins and other
molecules.
• It is surrounded by a
nuclear envelop that is also
a lipid bilayer.
• Chromosomes keep all of
the genetic info.
• Nucleolus forms
ribosomes.
Cell Organelles
• Ribosomes-site of
protein synthesis
• Endoplasmic Reticulum ERInternal membrane system.
– Rough- has ribosomes
• Makes new cell membranes
– Smooth- no ribosomes
• Makes lipids, processes
carbs and proteins, and
modifies toxic chemicals to
the cell.
The Golgi Body
• Golgi apparatus- series
of flat, membranebound sacs where
proteins and other
molecules from the
ER are sorted,
modified, packaged,
and distributed to their
destination for storage
or secretion.
Lysosomes
• Contain digestive enzymes
that help break down large
molecules of carbs,
proteins, and lipids.
• They also digest old
organelles no longer
useful.
• Lysosome function
– Go to cellular function and
structure and click on
lysosomes
Vacuoles
• Saclike structure that
stores materials such
as water, salts,
proteins and carbs.
• In plants it takes up
90% of the
volume…why?
Mitochondria
• Change the energy
stored in food
compounds into a
form useful for the
cell. (Where ATP is
made.)
• Also known as “The
Power House.”
Take a quiz over the organelles here
1.13 Some organelles in modern eukaryotes
developed from early prokaryotes: Mitochondria,
and chloroplast (in plants).
• American biologist
Lynn Margulis
proposed the
endosymbiotic theory.
Chloroplast
• It suggested that ancient
prokaryotes similar to
mitochondria and
chloroplasts began a
symbiotic relationship in a
host cell. Eventually these
prokaryotes started to
function as organelles in the
host cells.
Plant vs. Animal Cells
• Plants
• Animals
– Have a tough, rigid outer
– Cell membrane
covering that maintains the cells
shape called the Cell Wall.
– Smaller vacuoles
Support and protection.
– Centrioles- help
– Chloroplasts enable the plant to
organize cell
make sugars through
photosynthesis.
division.
– Central vacuole absorb water,
store proteins, ions, and waste
products.
Compare animal
Tablecells
3.6 page 70
and plant
Photosynthesis vs. Cellular
Respiration
• Photosynthesis
Captures energy
(converts light energy
into chemical energyATP)
Chloroplasts
• Cellular Respiration
Releases energy (ATP)
Mitochondria
• C6H12O6 + 6O2 
6CO2 + 6H2O
• 6CO2 + 6H2O 
C6H12O6 + 6O2
1.3, 1.4, 1.9, 1.43
Eukaryotic Organelles
• Go to the following link for a tutorial on
eukaryotic organelles.
• Eukaryotic Organelles
1.2b Flagella and Cilia allow some Protista, Monera,
and animal cells to move.
Flagella in Motion
Movement
• Cilia- short, hair-like
projections that
usually occur in large
numbers on the
surface of certain
cells.
• Flagella- long, tail-like
projections that move
in a whip-like motion
in eukaryotes and in
prokaryotes they spin
like a propeller.
1.5 Most cells have a narrow range of temperature and acidity
that they can survive. If there are extreme changes in the
environment, they may alter the structure of the protein and
the cells function.
1.15 In biological systems, STRUCTURE DETERMINES
FUNCTION.
It is very important to understand the conditions have to be
“right” for cells to function properly. If it gets too hot, too
cold, too acidic, or too basic, the cell may die or because
the conditions denature or alternate the structure of the
protein, the function is altered.
Cell Membranes and Their
Environment
• A semipermeable
membrane allows certain
molecules to pass through
and others not.
– Passive transport- no
energy used
– Active- energy used
– Active and Passive
transport
Diffusion
• Diffusion is the random
movement of molecules from
an area of higher
concentration to an area of
lower concentration.
• It always occurs down a
concentration gradient.
• It continues until the system
has reached equilibrium.
• Membrane transport- go to
cellular transport and click on
membrane transport.
• Facilitated
diffusion is a
form of passive
transport that
uses carrier
proteins in the
membrane.
Will increasing the temp. speed up
or slow down diffusion?
Osmosis
• Osmosis is the
diffusion of water
across a
semipermeable
membrane.
• 3 types of solutions
– Hypertonic- [solutes] are
higher on the outside than the
inside.
– Hypotonic-[solutes] are
lower on the outside than the
inside.
– Isotonic- [solutes]=[on the
inside]
What do you think will happen
in each?
Osmosis and Penicillin
• Penicillin, one of the most important antibiotic drugs
in the history of medicine, depends on osmosis for
its killing action.
• Pencillin inhibits an enzyme with which many
bacteria produce chemical cross-links in their cell
walls.
• This leads to the formation of a weakened cell wall
that cannot stand the stress of osmotic pressure.
• The cell wall becomes weaker and breaks. The
bacterium bursts under the inrush of water caused by
osmosis.
Active Transport
• Uses energy to move
molecules across the
membrane against the
concentration gradient.
Lower to Higher.
• It requires carrier
proteins and ATP.
Bulk Transport of Materials
• Exocytosis- movement of
materials out of the cell.
• Endocytosis- movement of
material into a cell.
– Pinocytosis- movment
of fluids into cell.
– Phagocytosis- engulfs
food particles into the
cell.
Cell Specialization
• Cells throughout an organism can develop
in different ways to perform different tasks.
• RBC- transport oxygen
• Pancreatic cells- produce insulin
• Muscle cells- contract and relax for body
movement.
• Guard cells- control opening and closing of
stomata on leaves for gas exchange.
Ch. 7 Review
• Click on your biology book, go to Unit 3
cells and click on Links and Self-Test.
• Cells Review
• Overview of cell and processes