Damn Near Everything There Is To Know About Cells:

Biology Cell Report

There are many parts of a cell, they all have specific duties, and are all
needed to continue the life of the cell. Some cells exist as single-celled
organisms that perform all of the organism\'s metabolism within a single cell.
Such single-celled organisms are called unicellular. Other organisms are
made up of many cells, with their cells specialized to perform distinct
metabolic functions. One cell within an organism may be adapted for movement,
while another cell carries out digestion. The individual cells no longer
carry out all life functions, but rather depend on each other. Many-celled
organisms are called multicellular. When a group of cells function together to
perform an activity, they form a tissue. The cells of a human are organized
into tissues such as muscle and nerve tissues. Plant tissues include those
of the stem and root. Many cells in tissues are linked to each other at
contact sites called cell junctions. Cell junctions help maintain differences
in the internal environment between adjacent cells, help anchor cells together,
and allow cells to communicate with one another by passing small molecules from
one cell to another. Groups of two or more tissues that function together
make up organs. An organ system is a group of organs that work together to
carry out major life functions.

Eukariotic Cell Structure:

Boundaries and Control:

Plasma Membrane - The plasma membrane is sometimes called the cell membrane, or
the cellular membrane. It is the outermost part of the animal cell, and it\'s
purpose is to enclose the cell, and change shape if needed. The cell membrane
is capable of allowing materials to enter and exit the cell. Oxygen and
nutrients enter, and waste products such as excess water leave. The plasma
membrane helps maintain a chemical balance within the cell.

Cell wall - The cell wall is an added boundary to the cell. It is relatively
inflexible, and surrounds the plasma membrane. The cell wall is much thinker
than the plasma membrane and is made of different substances in different
organisms. The cells of plants, fungi, almost all bacteria, and some protists
have cell walls. Animal cells have no cell walls. Plant cells contain
cellulose molecules, which form fibers. This fibrous cellulose of plants
provides the bulk of the fiber in our diets. Chitin, a nitrogen-containing
polysaccharide, makes up the cell walls of fungi.

Nucleus - The nucleus of the cell is the organelle that manages cell functions
in a eukariotic cell. The nucleus contains DNA, the master instructions for
building proteins. DNA forms tangles of long strands called chromatin, which is
packed into identifiable chromosomes when the cells are ready to reproduce.
Also within the nucleus is the nucleolus, a region that produces tiny cell
particles that are involved in protein synthesis These particles, called
ribosome\'s, are the sites where the cell assembles enzymes and other proteins
according to directions of the DNA.

Assembly, Transport, and Storage:

Cytoplasm - The material that lies outside the nucleus and surrounds the
organelles is the cytoplasm, a clear fluid that is a bit thinner than toothpaste
gel. It usually constitutes a little more than half the volume of a typical
animal cell.

Endoplasmic Reticulum - The endoplasmic reticulum (ER) is a folded membrane that
forms a network of interconnected compartments inside the cell. The ER
membranes contain the enzymes for almost all of the cell\'s lipid synthesis, they
serve as the site of lipid synthesis in the cell. The ER functions as the
cell\'s delivery system. Some parts of the ER are studded with ribosome\'s. In
the cell, the sites of protein assembly are the ribosome\'s.

Golgi Apparatus - The Golgi apparatus\'s main purpose is to store materials. The
Golgi apparatus is a series of closely stacked, flattened membrane sacs that
receives newly synthesized proteins and lipids from the ER and distributes them
to the plasma membrane and other cell organelles. Proteins are transferred from
the ER to the Golgi apparatus in small, membrane-bound transport packages.
These packages, called vesicles, have pinched off from the membrane of the ER
and contain proteins. The Golgi apparatus modifies the proteins chemically,
then repackages them in new vesicles for their final destination in the cell.
They may be incorporated into the cell structures, expelled, or remain stored
for later usage.

Vacuole - A vacuole is a sac of fluid surrounded by a membrane. Vacuoles often
store food, enzymes, and other materials needed by cells, and some vacuoles
store waste products. A plant cell has one large vacuole that stores water and
other substances.

Lysosomes - In addition to the assembly and storage of macromolecules, cells
also can disassemble things.