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Cell in detail

An electrochemical
cell is a setup used for creating an electromotive force in a
conductor separating two reactions. The current is caused by the reactions
releasing and accepting electrons in to the different ends of the conductor.
The most common example of an electrochemical cell is a standard 1.5-volt battery.
In each half-cell is a chemical undergoing either oxidation or reduction.
In a full electrochemical cell one side must be losing electrons (oxidation)
in to its electrode, while the other half-cell gains electrons (reduction.)
If the atoms/ions involved in the reaction are metal, the same metal
is used for each electrode. If the atoms/ions involved in the reaction
at each half-cell are not metal, obviously no electrode can be constructed
out of it. Nonreactive metals such as platinum are used as a substitute.
Finally a salt bridge is necessary to provide electrical contact between
the cells--but without the solutions mixing. This can simply be a strip
of filter paper soaked in saturated potassium nitrate (V) solution.
Different choices of substances for each half cell results in varying
potential differences. Each reaction is undergoing an equilibrium reaction
between different oxidation states of the ions -- when equilibrium is
reached the cell cannot provide further voltage. In the half-cell, which
is undergoing oxidation, the closer the equilibrium, lies to the ion/atom
with the more positive oxidation state the more potential this reaction
will provide. Similarly, in the reduction reaction, the further the
equilibrium lies to the ion/atom with the more negative oxidation state the higher the potential. This potential
can be predicted quantitatively through the use of electrode potentials
(the voltage measured when the substance is connected to hydrogen.)
The difference in voltage between electrode potentials gives a prediction
for the potential measured.

A conventional definition of life

A life
form has traditionally been considered to exhibit all the following
phenomena at least once during its existence:

Growth
Metabolism, consuming, transforming and storing
energy/mass; growing by absorbing and reorganizing mass; excreting waste
Motion, either moving itself, or having internal
motion
Reproduction, the ability to create entities that
are similar to itself
Response to stimuli - the ability to measure properties
of its surrounding environment, and act upon certain conditions.

Image of nucleus, endoplasmic reticulum and Golgi apparatus. 

(1) Nucleus. (2) Nuclear pore. (3) Rough endoplasmic reticulum (RER).
(4) Smooth endoplasmic reticulum (SER). (5) Ribosome on the rough ER.
(6) Proteins that are transported. (7) Transport vesicle. (8) Golgi
apparatus. (9) Cis face of the Golgi apparatus. (10) Trans face of the
Golgi apparatus. (11) Cisternae of the Golgi apparatus.

The cell in life science is the structural and
functional unit of all living organisms, sometimes called
the "building blocks of life." Organisms, such as humans,
are multicellular, (humans have an estimated 100,000 billion = 10<sup>14
cells). Cells come from preexisting cells; all vital functions occur
within cells and cells contain the hereditary information (DNA) (Heredity
-the adjective is hereditary- is the
transfer of characteristics from parent to offspring, through genes) necessary for regulating cell functions and for transmitting information
to the next generation of cells. Each cell is at least somewhat self-contained
and self-maintaining: it can take in nutrients, convert these nutrients
into energy, carry out specialized functions, and reproduce as necessary.
Each cell stores its own set of instructions for carrying out each of
these activities. Cells also have a set of "little organs",
called organelles, which are adapted and/or specialized for carrying
out one or more vital functions.

All cells share several abilities:

Reproduction by cell division.
Metabolism, including taking in raw materials, building
cell components, creating energy molecules and releasing by-products.
The functioning of a cell depends upon its ability to extract and use
chemical energy stored in organic molecules. This energy is derived
from metabolic pathways.
Synthesis of proteins, the functional workhorses
of cells, such as enzymes. A typical mammalian cell contains up to 10,000
different proteins.
Response to external and internal stimuli such as
changes in temperature, pH or nutrient levels.
Traffic of vesicles.

Sub cellular components

Schematic of typical animal
cell, showing subcellular components. Organelles: (1) nucleolus (2)
nucleus (3) ribosome (4) vesicle, (5) rough endoplasmic reticulum (ER),
(6) Golgi apparatus, (7) Cytoskeleton, (8) smooth ER, (9) mitochondria,
(10) vacuole, (11) cytoplasm, (12) lysosome, (13) centrioles

All eukaryotic (such as human) cells have a membrane,
which envelopes the cell, separates its interior from its environment,
controls what moves in and out, and maintains the electric potential
of the cell. Inside the membrane, a salty cytoplasm takes up most of
the cell volume. All cells possess DNA, (the hereditary material of
genes) and RNA, (which contain the information necessary to build various
proteins such as enzymes), as the cell's primary machinery.

Cell membrane

The
cytoplasm of a eukaryotic cell is surrounded by a plasma membrane. A form of plasma membrane is also found in
prokaryotes, but is usually referred to as the cell membrane. This membrane serves to separate and protect
a cell from its surrounding environment and is made mostly from a double
layer of lipids (fat-like molecules) and proteins. Embedded within this
membrane are a variety of other molecules that act as channels and pumps,
moving different molecules into and out of the cell.

Cytoskeleton - a cell's scaffold

The
cytoskeleton is an important, complex, and dynamic cell component. It
acts to organize and maintain the cell's shape; anchors organelles in
place; helps during endocytosis, the uptake of external materials by
a cell; and moves parts of the cell in processes of growth and motility.
There are a great number of proteins associated with the cytoskeleton,
each controlling a cell's structure by directing, bundling, and aligning
filaments.

Cytoplasm - a cell's inner space

Inside
the cell there is a large fluid-filled space called the cytoplasm, which
includes both to the mixture of ions and fluids in solution within the
cell, and to the organelles contained in it. The term cytosol refers only to the fluid itself. In prokaryotes, the
cytoplasm is relatively free of compartments. In eukaryotes, it normally
contains a large number of organelles. The cytosol contains dissolved
nutrients, helps break down waste produc