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Cells
Cell Theory
The cell theory is a widely accepted explanation of the relationship
between cells and living things. The cell theory states:
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All living things are made of cells.
New cells are created by old cells dividing into two.
Cells are the basic building units of life.
Types of Cells
 Prokaryotic- simpler cells such as viruses
and bacteria that do not have a nucleus
 Eukaryotic- more complex cells found in
plants and animals that contain a nucleus
Cells Have Basic Needs
Living organisms have basic needs because their cells have basic needs.
Cells, like organisms, typically need:
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water
nutrients/food
an environment in which they can live
a means of removing the waste
Typical Plant Cell
nucleolus
nuclear membrane
mitochondrion
nucleus
endoplasmic reticula
ribosomes
cell membrane
chromatin
cell wall
cytoplasm
chloroplast
vacuole
Organelle
Structure
Function
Analogy
cell wall
rigid and flexible layer
that surrounds and
protects plant cells
Strong wall that protects
a city
cell membrane
selectively permeable
layer (controls what
enters or leaves)
guards that control who
enters or leaves
cytoplasm
gel-like fluid that fills
the cell and surrounds
the organelles
the space filling up the
inside of the city
Organelle
Function
Analogy
nucleus
directs all of the cell’s
activities; the “brain”
of the cell
Town hall building which
controls the city
nucleolus
found in the nucleus;
produces ribosomes
and proteins
Carpenters which build
the workshops; their
office is in the town hall
chromatin
found in the nucleus;
contain the
“instructions” to run
the cell
produce proteins;
found floating in
cytoplasm or attached
to the endoplasmic
reticula
site of cellular
respiration; where
sugars are broken
down for energy
contain chlorophyll and
give plants green color;
where photosynthesis
occurs
break down food or
toxic molecules
the blueprints or data
base used to run the city
golgi body
packages the proteins
made by the ribosomes
to be sent to other
parts of the cell
the mail room
endoplasmic
reticulum
system of passageways
that move materials
like proteins around
the cell
the transportation
system
vacuoles
storage area for food,
water and waste in a
cell; help plants remain
ridgid
the water tower
ribosomes
mitochondria
chloroplasts
lysosomes
Structure
workshops that produce
city’s main product
(widgets)
the power plant of the
cell
the solar panels that
make energy from
sunlight
the maintenance crew
Although some cells contain a different assortment of organelles than
others, a list of the organelles commonly found in most plant and animal
cells appears below:
 Cytoplasm is a gel-like fluid that fills the cell and surrounds the other
organelles.
 Nucleus is like the “brain” of the cell. It contains chromosomal
information on chromatin. Chromatin is composed of long, thin
strands of DNA which contains “instructions” that control cell
metabolism and heredity.
 Ribosomes are small grain-like bodies that produce proteins.
 Mitochondria take in nutrients, break them down during cellular
respiration, and create energy for the cell.
 Chloroplasts are the food producers in a plant cell. During a process
known as photosynthesis, chloroplasts absorb light energy from the
Sun and produce food in the form of glucose sugar from carbon
dioxide and water.
 Endoplasmic reticula transport chemicals between and within cells.
 Vacuoles store water and ingested food in a fluid sack. They also
remove wastes from cells and produce turgor pressure against the
cell wall for cellular support.
 Lysosomes contain enzymes specialized to break down ingested
materials, secretions, and wastes.
 Golgi bodies (or Golgi apparatus) process cellular wastes and other
materials and transport them out of the cell. In addition to playing an
important role in waste disposal, Golgi bodies also process, sort, and
modify proteins in cells.
 The cell membrane (or plasma membrane) acts as a boundary layer
around the cytoplasm thus separating cells from their outside
environments. In addition to being able to recognize chemical signals,
the cell membrane is selectively permeable to chemicals and controls
which molecules enter and leave the cell. Nutrients first enter the cell
through the cell membrane.
 The cell wall is a secretion of the cell membrane. It provides
protection from physical injury, and with the vacuole, it provides
structural support.
Plant cells and animal cells contain different cellular structures. For
example, most plant cells possess a cell wall and chloroplasts. Animal
cells never contain these structures. Plant cells also always contain large
vacuoles. Some animal cells also have vacuoles, but the vacuoles in
animal cells are much smaller than those found in plant cells.
Photosynthesis
Plants are autotrophs, organisms that make their own food. During
photosynthesis, plants use energy from the sun to convert carbon
dioxide and water into oxygen and sugars. Sunlight is captured by the
chloroplasts where it is absorbed by a green pigment, chlorophyll. The
plant then uses two other raw materials, water (H2O) and Carbon
Dioxide (CO2) to create the glucose (a type of sugar). The H2O comes
from the roots through the xylem. The CO2 comes from openings on the
bottom of the leaf called stomata.
Respiration
Respiration is the process by which cells produce energy from glucose.
Cells break down glucose and release the energy that it contains. This
process happens continuously in the mitochondria.
Fermentation
Some cells obtain their energy through fermentation, an energy
releasing process that does not require oxygen. Fermentation provides
energy for cells without using oxygen. One type of fermentation occurs
in yeast and some other single-celled organisms. This process is
sometimes called alcoholic fermentation because alcohol is one of the
products made when these organisms break down sugars. Another type
of fermentation takes place at times in your body, for example, when
you’ve run as fast as you could for as long as you could. One product of
this type of fermentation is an acid known as lactic acid. When lactic acid
builds up, your muscles feel weak and sore.