cell membrane

1. Cells are the smallest units of life, we explore the
characteristics, components, and functions of cells.
Learning about the structures of cells allows us to
see the similarities and differences among
organisms.
Bacteria, plant, animal, and fungus cells are similar
in many ways and contain many of the same small
structures known as organelles.
However, some characteristics help distinguish
whether a cell belongs to an animal, plant, fungus,
or bacteria. For example, all plant cells contain cell
walls, while animal cells lack this particular
extracellular structure. The water within a cell that
presses against the cell wall gives a plant its rigidity
and your celery its crunch!
Cells and Cell Membranes
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2. Cellular Organization and Organelles
Studying Cells
A cell is the smallest unit of a living
thing.
A living thing, whether made of
one cell (like bacteria) or many
cells (like a human), is called an
organism. Thus
cells are the basic building blocks
of all organisms.
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3. Several cells of one kind that interconnect
with each other and perform a shared
function form tissues, several tissues
combine to form an organ (your stomach,
heart, or brain), and several organs make
up an organ system (such as the digestive
system, circulatory system, or nervous
system).
Several systems that function together
form an organism (like a human being).
we will examine the structure and function
of cells.
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4. There are many types of cells, all
grouped into one of two broad
categories: prokaryotic and
eukaryotic.
For example, both animal and plant
cells are classified as eukaryotic
cells,
whereas bacterial cells are
classified as prokaryotic. Before
discussing the criteria for
determining whether a cell is
prokaryotic or eukaryotic, let's first
examine how biologists study cells.
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5. Microscopy
Cells vary in size. With few
exceptions, individual cells cannot
be seen with the naked eye, so
scientists use microscopes (micro-
= "small"; -scope = "to look at") to
study them.
A microscope is an instrument that
magnifies an object. Most
photographs of cells are taken with
a microscope, and these images
can also be called micrographs.
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6. The optics of a microscope's lenses
change the orientation of the
image that the user sees
. A specimen that is right-side up
and facing right on the microscope
slide will appear upside-down and
facing left when viewed through a
microscope, and vice versa.
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7. Light Microscopes
To give you a sense of cell size, a
typical human red blood cell is
about eight millionths of a meter
or eight micrometers (abbreviated
as eight μm) in diameter; the head
of a pin of is about two
thousandths of a meter (two mm)
in diameter. That means about 250
red blood cells could fit on the
head of a pin.
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8. Electron Microscopes
In contrast to light microscopes, electron
microscopes use a beam of electrons instead of a
beam of light. Not only does this allow for higher
magnification and, thus, more detail it also provides
higher resolving power. The method used to
prepare the specimen for viewing with an electron
microscope kills the specimen. Electrons have short
wavelengths (shorter than photons) that move best
in a vacuum, so living cells cannot be viewed with
an electron microscope.
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9. In a scanning electron microscope,
a beam of electrons moves back
and forth across a cell's surface,
creating details of cell surface
characteristics.
In a transmission electron
microscope, the electron beam
penetrates the cell and provides
details of a cell's internal
structures.
As you might imagine, electron
microscopes are significantly more
bulky and expensive than light
microscopes
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10. Cell Theory
The microscopes we use today are
far more complex than those used
in the 1600s by Antony van
Leeuwenhoek, a Dutch shopkeeper
who had great skill in crafting
lenses. Despite the limitations of
his now-ancient lenses, van
Leeuwenhoek observed the
movements of Protista (a type of
single-celled organism) and sperm,
which he collectively termed
"animalcules".
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11. In a 1665 publication
called Micrographia, experimental
scientist Robert Hooke coined the
term "cell" for the box-like
structures he observed when
viewing cork tissue through a lens.
In the 1670s, van Leeuwenhoek
discovered bacteria and protozoa.
Later advances in lenses,
microscope construction, and
staining techniques enabled other
scientists to see some components
inside cells.
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12. By the late 1830s, botanist
Matthias Schleiden and zoologist
Theodor Schwann were studying
tissues and proposed the
unified cell theory, which states
that all living things are composed
of one or more cells, the cell is the
basic unit of life, and new cells
arise from existing cells.
Rudolf Virchow later made
important contributions to this
theory.
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13. Parts of a Cell
Cell membrane: The cell membrane is the outer
boundary of the cell. It controls what enters and
leaves the cell.
Cytoplasm : The cytoplasm is the
jelly-like substance that fills the
cell. It contains all of the organelles
of the cell.
Nucleus : The nucleus is the
control center of the cell. It
contains the cell's DNA, which is
the genetic material that tells the
cell how to function.
Nucleolus : The nucleolus is a small
structure inside the nucleus that
makes ribosomes. Ribosomes are
the organelles that make proteins
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14. Ribosomes : Ribosomes are the
protein-making factories of the
cell. They read the instructions
from the cell's DNA and use them
to make proteins.
Endoplasmic reticulum (ER):The
endoplasmic reticulum is a
network of membranes that
transport materials throughout the
cell. There are two types of ER:
rough ER and smooth ER. Rough ER
has ribosomes attached to it, while
smooth ER does not.
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15. Golgi apparatus : The Golgi
apparatus is a packaging and
shipping center for the cell. It
modifies, sorts, and packages
proteins and other materials made
by the ER for transport to other
parts of the cell or out of the cell.
Mitochondria : Mitochondria are the
cell's powerhouses. They break
down food molecules and release
energy that the cell can use to carry
out its functions
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16. Vacuoles : Vacuoles are storage
sacs in the cell. They can store
water, food, waste products, and
other materials.
Lysosomes : Lysosomes are the
cell's garbage disposal units. They
break down old cell parts, waste
products, and foreign invaders.
Cytoskeleton : The cytoskeleton is
a network of fibers that helps to
support the cell and give it its
shape. It also helps the cell to
move.
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