Download Cells


The discovery of cells
› Cells
 All living things are composed of cells.
 Cells are the smallest unit that can carry
on the processes of life.
 Beginning in the 17th century naturalists
were able to use microscopes to study
objects too small to be seen by the
naked eye.
› Robert Hooke
 Studied nature using
an early light
microscope.
 Looked at thin slice of
cork from the bark of
a cork oak tree
 Saw little boxes,
cubbies or cells
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Anton Van
Leeuwenhoek
› First person to observe
living cells
› Made microscopes
that were simple and
tiny, but he ground
the lenses so precisely
that the
magnification was 10
times that of Hooke’s
instruments.
› He discovered protists
or one celled
organisms.
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Although Hooke and
Leeuwenhoek were the first to
observe cells, their
observations were not realized
until 150 years later.
1838 Matthias Schleiden
concluded that all plants
were composed of cells.
1839 Theodor Schwann
concluded that animals were
composed of cells.
Rudolph Virchow noted that
all cells come from other cells.
These three observations were
combined to create the CELL
THEORY.
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3 ESSENTIAL PARTS
 All living organisms
are composed of
one or more cells.
 Cells are the basic
unit of structure
and function in an
organism.
 Cells come only
from the
reproduction of
existing cells.
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Cells within different organisms and within
the same organism are very different and
diverse in terms of shape size, and internal
organization.
› Shape
 Diversity in shapes reflects the different
functions of cells.
 Diversity
in shapes
reflects the
different functions
of cells.
 Cell shape can
be simple to
complex.
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The size of a cell is limited by the relationship of the cell’s outer
surface area to its volume or its surface area – to – volume ratio.
As cells grow its volume increase much faster than its surface area.
Important because the materials needed by a cell and the waste
produced by the cell must pass into and out of the cell through its
surface.
› If a cell were to become very large, the volume would increase
much more that the surface area. Therefore the surface area
would not allow materials to enter or exit the cell quickly enough to
meet the cell’s needs. As a result most cells are microscopic in size.
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Cells have three basic
features that are
common to all types.
› Outer boundary
 Cells outer boundary is
called the plasma
membrane or the cell
membrane.
 Covers the cells
surface and acts as a
barrier between the
inside and outside of a
cell.
 All materials enter and
exit through the
plasma membrane.
› Interior substance
 The region of the cell
that is within the
plasma membrane
and that includes the
fluid, the cytoskeleton,
and all of the other
organelles except the
nucleus is called the
cytoplasm.
 The part of the
cytoplasm that
includes molecules
and small particles,
such as ribosomes, but
not membrane bound
organelles is the
cytosol.
 Cells carry coded
information in the form of
DNA for regulating
function and
reproduction.
 DNA is some cells moves
freely inside while others
have DNA in a organelle
called the nucleus.
 Most of the functions of
the eukaryotic cell are
controlled by the nucleus.
 Often the biggest
structure in the cell.
 Maintains shape with the
help of a protein skeleton
called the nuclear matrix
or nuclear envelope.
Nuclues
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Prokaryotes
› Organisms that lack a
membrane-bound
nucleus and membrane
bound organelle.
› Although prokaryotic
cells do not have a
nucleus, their genetic
information – in the form
of DNA – is concentrated
in a part of the cell called
the nucleoid.
› Prokaryotes are divided
into 2 domains: Bacteria
and Archaea.
 Bacteria includes
organisms that are similar
to the first life-forms.
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Eukaryotes
› Organisms made up of
one or more cells that
have a nucleus and
membrane-bound
organelles.
› Have a variety of subcellular structures called
organelles.
 Organelles are well
defined, intracellular
bodies that perform
specific functions for a cell.
 Many organelles are
surrounded by membranes.
 Generally much larger than
prokaryotes
Over time cells began to form groups
that function together.
 Some retained the ability to live outside
a group.
 Others became dependent on each
other for survival.
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Colonies
› A colonial organism
is a collection of
genetically identical
cells that live
together in a
connected group.
› They are not truly
multi-cellular
because few cell
activities are
coordinated.
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True multicellularity
› As organisms evolved, cells became more specialized and eventually
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could not survive independently.
Groups of cells took on specific roles or functions within the organism.
Groups of cells and their products that carry out specific functions are
called tissues.
Groups of tissues that perform a particular function or job within an
organism are celled organs.
An organ system is a group of organs that accomplish related tasks.
An organism is a collective of organ systems that carry out the
processes of life.