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Look around you. What do
you see? A classmate, a
brother or sister? Look out
the window, or go for a
walk. You will see trees,
grass, plants, dogs, cats,
bugs, and many other forms
of life
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From many kilometers (miles) into the
atmosphere, to many meters (feet) beneath the
surface of the Earth, life is everywhere.
What is this stuff we call life?
What are some things that all life forms have in
common?
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These cells are the basic building blocks
of life. As an example, have you ever seen
a sand castle?
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At a distance, the sand
castle looks like a
smooth brown
building. As you get
closer to the sand
castle, you can begin
to see that it is not one
smooth building, but
instead that it is made
up of millions of tiny
grains of sand.
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Looking at an elephant, you might see what looks
like a smooth gray animal. And it is true that this is
what you are seeing. However, just like the sand
castle, if you could get close enough, and if your
eyes were powerful enough, you would realize that
what looks like a smooth gray surface, is really
made up of many billions of smaller objects called
cells.
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Cells are tiny units of living materials
separated by a cellular wall, or barrier.
These cells are so small, that they can only
be seen with a powerful tool known as a
microscope. Cells make up every part of a
living thing. Your skin, your hair,
fingernails, blood, bones, nerves, and
muscles are all made up of cells. These
cells work together to keep the life form
alive.
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A tissue is a family of cells that live very close
together, and work hard to do the same jobs.
Many tissues come together to form what
biologists call an organ. This is like a city in the
example below. Organs then work together to
form a system, and eventually the entire body of a
life form.
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In a way, your body is functioning as a
mini-planet. Right now within your body,
there are billions of individual cells
working hard in specialized jobs. These
cells join into tissues, organs, and
systems and help make up a vast
community of life within you.
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You are very fortunate to have been
born when you were. Throughout most
of human history, scientists knew very
little about life, and how it works. It was
not until 1665 that a scientist by the
name of Robert Hooke first discovered
the existence of cells.
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While using the newly invented
compound microscope to look at a thin
slice of cork, Hooke saw tiny room like
structures that he named cells. The cells
that Mr. Hooke saw through his
microscope were all dead, because the
cork came from a plant that had long
since died.
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Nearby a Dutch scientist by the name of
Anton Van Leeuwenhoek was also using
his microscope to look at things. Anton
Van Leeuwenhoek decided to try and
look at things that were still alive, like
blood, and saliva from his mouth. Mr.
Leeuwenhoek all looked at rainwater
through his microscope.
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What did Anton Van Leeuwenhoek see
through his microscope? He was
surprised to find what looked like tiny
animals. He named these animals
“animalcules”.
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Today scientists have developed what
we call the Cell Theory. This theory
states the following:
◦ All living things are made of cells.
◦ Cells are the basic units of structure and
function in living things.
◦ Living cells come only from other living cells.
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Inside a cell are tiny organs called
organelles The word organelle is a big
word that means small organ.
These organelles function to provide for
the needs of the cell.
They work to bring in food supplies, get
ride of waist, protect the cell, repair the
cell, and help it grow and reproduce.
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Cells vary in size, your body cells range
in size from 5-20 um.
Cells are small because:
◦ They must function efficiently.
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Cell size is limited by two factors:
◦ Surface area-to-volume relationships that
make distribution of materials throughout a
large cell difficult;
◦ The volume of cytoplasm the nucleus can
control.
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Most cells are small because larger cells do not
function as efficiently
◦ larger cells are more difficult to control because of the
distances involved from the command center at the
core to the peripheral regions
◦ organisms that are comprised of many, small cells are
at an efficiency advantage over organisms comprised of
few, larger cells
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The first cell
structure we will
explore is the cell
wall. Found only in
plant cells, the cell
wall provides the
cell with additional
strength. Cell walls
are thick walls built
around the cell.
These walls are
made from
cellulose.
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Enclosed by a plasma
membrane and
containing a membranebound nucleus and
organelles.
Can’t make their own
food
The animal cells use the
food to make the energy
they need to reproduce
and carry out basic
functions. This process
takes place in a part of
the cell called the
mitochondrion.
Only Animals cells
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Centrioles (helps in cell division)
Only Plant Cells
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A single, large vacuole ( up to 90% of volume).
Cell Wall surrounding the plasma membrane (made of
cellulose).
Chloroplast (contains chlorophyll for photosynthesis).
Brick-like shape (due to cell wall).
The main difference is that animal cells only have a cell
membrane, while plant cells have a cell wall and cell
membrane.
Typical animal cell
Typical plant cell
•Nucleus
•Nucleolus (within nucleus)
•Rough endoplasmic reticulum
(ER)
•Smooth ER
•Ribosomes
•Cytoskeleton
•Golgi apparatus
•Cytoplasm
•Mitochondria
•Vesicles
•Lysosomes
•Centrosome
•Centrioles
•Nucleus
•Nucleolus (within
nucleus)
•Rough ER
•Smooth ER
•Ribosomes
•Cytoskeleton
•Golgi apparatus
(dictiosomes)
•Cytoplasm
•Mitochondria
•Vacuoles
•Cell wall
Organelles
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Think about how a plant
grows. Plants grow tall,
towards the Sun's light.
In order to provide
plants with the strength
necessary to support
their weight, the cells
within the plant have
this hard cell covering.
If a tree were soft and
mushy like an animal, do
you think they could
stand strong and tall?
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If an animal's body were made of plant cells,
the animal would be very stiff, and unable to
move easily.
Instead of cell walls, animals use other
creative solutions to give them strength. For
example, many animal's bodies are built on a
structure of bones.
These bones allow the animal to have the
strength to stand up, but the flexibility to
move quickly.
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Two types of cells:
◦ Prokaryotic
◦ Eukaryotic
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Lack a nucleus
Do not have an extensive system of interior
membranes or compartments
No organelles (membrane bound
compartments)
Have ribosomes (protein production)
Ex. Bacteria
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Other structures sometimes found in prokaryotes
relate to locomotion, feeding, or genetic
exchange
◦ flagellum (plural, flagellae) is a threadlike structure of
protein fibers that extends from the cell surface
 may be one or many
 aids in locomotion and feeding
◦ pilus (plural, pili) is a short flagellum
 aids in attaching to substrates and in exchanging genetic
information between cells
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Eukaryotic cells are larger and more complex
than prokaryotic cells
◦ have a plasma membrane encasing a cytoplasm
 internal membranes form compartments called
organelles
 the cytoplasm is semi-fluid and contains a network of
protein fibers that form a scaffold called a
cytoskeleton
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many organelles are immediately
conspicuous under the microscope
◦ nucleus
 a membrane-bounded compartment for DNA that
gives eukaryotes (literally, “true-nut”) their name
◦ endomembrane system
 gives rise to the internal membranes found in the cell
 each compartment can provide specific conditions
favoring a particular process
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not all eukaryotic cells are alike
◦ the cells of plants, fungi, and many protists have a
cell wall beyond the plasma membrane
◦ all plants and many protists contain organelles
called chloroplasts
◦ plants contain a central vacuole
◦ animal cells contain centrioles
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All cells are surrounded by a plasma membrane
composed of a bilayer of phospholipids.
The polar ends of these phospholipids interact
with the interior and exterior fluid environments of
the cell and the nonpolar fatty acid chains form the
interior of the membrane.
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Proteins within the membrane:
◦ Transmembrane proteins: function as transport
mechanism across the membrane.
◦ Cell surface proteins: serve as identification markers in
cell communication.
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Membrane defects can cause disease such as
cystic fibrosis (chloride ion transport not carried
out correctly)
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A phospholipid has a
polar head and two nonpolar tails
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The polar region contains
a phosphate chemical
group and is watersoluble
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The nonpolar region is
comprised of fatty acids
and is water-insoluble
Figure 5.4(a) Phospholipid
structure
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A lipid bilayer forms spontaneously whenever a
collection of phospholipids is placed in water
Figure 5.5 The lipid bilayer.
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The interior of the lipid bilayer is completely
nonpolar
◦ no water-soluble molecules can cross through it
◦ cholesterol is also found in the interior
 it affects the fluid nature of the membrane
 its accumulation in the walls of blood vessels can cause
plaques
 plaques lead to cardiovascular disease
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Found in both plant and animal cells, the cell
membrane is the outside wall of a cell.
In plant cells, it is a second wall, and is found
just inside the main cell wall.
The cell membranes found in animal cells
contain a chemical called cholesterol. This
chemical makes the membrane harder.
Plant cells do not need cholesterol, because
they have a cell wall, as a result, their cell
membranes are softer.
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In order for a cell to
remain healthy, the cell
needs to be able to
bring in food, and get
ride of waste.
Look closely at this
picture. You will notice
that the cell membrane
has small openings or
doorways.
These openings allow
the cells to move
materials in and out of
the cell.
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As you travel through the cell membrane and
enter the cell, you will find yourself floating in
a kind of jelly. This jelly that fills the inside of
a cell is called Cytoplasm.
Cytoplasm helps to hold the cell's organelles
(small organs) in place.
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Cytoplasm also gives the cell structure. Think
of a balloon. An empty balloon does not have
much structure. However, if we fill it with
something, like water, it begins to take
shape.
Cytoplasm also helps the cell move proteins,
chromosomes and other materials including
the cells organelles around the cell.
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How do you travel from home to school? Do
you take a road, or sidewalk? Roads and
sidewalks give people a path to follow as we
move about our cities. A cell also has a
system of tiny roads. These roads are actually
tubes called the Endoplasmic Reticulum.
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These clear tubes travel
throughout all parts of
the cell. Some go from
the nuclear membrane
to the outside cellular
membrane. Others
travel to different
organelles. Throughout
the cell, the
endoplasmic reticulum
carries materials where
they need to go.
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As you travel along the endoplasmic
reticulum you will notice that stuck
to the side of this tube, are several
small balls called Ribosomes.
Ribosomes use available materials
to build proteins.
These proteins can then be used by
the cell for other purposes, such as
to build new structures, repair
damage, and direct chemical
reactions.
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Why do you think ribosomes are found on the
walls of the endoplasmic reticulum? Think
about it. Remember, the endoplasmic
reticulum is the cell's transportation system.
When a ribosome is done building a protein,
it can release it directly into the endoplasmic
reticulum, where it can then be transported to
wherever it is needed.
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As you travel through the endoplasmic
reticulum look out into the cytoplasm. You
will see small round objects called
Lysosomes.
Lysosomes are filled with enzymes that are
used to break up and partially digest food.
The food particles are broken up into smaller
pieces, which can then be passed on to
another organelle called mitochondria. We
will learn about the mitochondria shortly.
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Another important job that the lysosomes
perform is to breakdown and digest older
parts of a cell. As a cell ages, parts of it need
to be replaced. The lysosomes breakdown the
old parts, so that the materials can be reused
to build new parts.
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The organelle responsible for energy
production inside a cell is called a
Mitochondrion (Plural: Mitochondria). These
pill shaped organelles take food, and break it
apart into water and carbon dioxide. As food
is broken down, an enormous amount of
energy is created.
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Think of the power generators that produce
electricity for our cities. As these power
generators break up fuel, they create
electricity which is captured, and transmitted
throughout the city.
Within living things, cells which are more
active need more energy. As a result, these
cells have more mitochondria. In a similar
way, bigger cities need more power, and as a
result, these cities have more power plants.
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The Golgi Apparatus is
responsible for taking the
proteins which were created by
the ribosomes, and making
them bigger and better. Think
of an assembly line, where cars
are made. The first worker
creates a car frame. The next
worker adds an engine, or
seats, or other parts.
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Ribosomes are like the first
worker in the pic. They create
basic proteins. The golgi
apparatus then takes these
proteins and adds to them,
making them bigger and
better.
When the golgi apparatus is
done, it releases the new
proteins into the cell, where
they can be used to
strengthen and build up the
cell.
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Vacuoles are small sacs are filled with food and
water. They are used by cells as storage tanks.
All plant cells have vacuoles, but not all animal
cells do.
The primary place where plants store water is
within its vacuoles.
When a plants vacuoles are filled with water,
they become plump, giving the plant strength.
What happens when you do not water a plant?
It begins to wilt, becoming softer. This is
because the vacuoles found inside the plants
cells are running out of water.
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When you look at a plant, what color do you
most often see? What makes plants green?
The last organelle we will explore is the
Chloroplast. A chloroplast is a small pill
shaped organelle found only in plants.
Chloroplasts are green because they are filled
with a green pigment, or chemical called
Chlorophyll. Chlorophyll is used by a plant to
capture energy from the sun, which can later
be used to create food.
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All living things are made of cells.
Cells make up all of the parts of an organism
and are responsible for everything that goes
on inside the organism.
Cell theory explains the connection between
cells and living things.
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1. All organisms are made up of cells.
2. Cells are the basic units that form the
structure and carry out the functions of all
organisms.
3. Cells are formed only from other cells.
4. Cells contain the genetic instructions of
organisms.
5. Cells control the metabolism and
biochemistry of organisms.
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Complex organisms are made up of billions
of tiny cells.
The structure of an organism depends on the
way its cells are arranged.
The variety of ways that cells are put together
accounts for the biodiversity of organisms.
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Cells are involved in all the processes in an
organism's body and carry out the
fundamental activities that make life possible.
Cells absorb nutrients and water, aid in
digestion, growth, production of biological
molecules, secretion, respiration, excretion of
wastes, generation of a membrane potential
or voltage, response to stimuli and
reproduction.
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The cell's nucleus acts like a brain to control
all of the cell's functions.
Within the nucleus are thin strands of genetic
material that contain the instructions for
directing all of the cell's activities.
Genetic information is passed from one
generation of cell to another when cells
divide.