Essay/Term paper: Damn near everything there is to know about cells:

Essay, term paper, research paper:  Biology

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. Lysosomes, organelles that contain digestive
enzymes, digest excess or worn out cell parts, food particles, and invading
viruses or bacteria.

Mitochondria - Mitochondria are organelles in which food molecules are broken
down to release energy. This energy is then stored in other molecules that can
power cell reactions easily. A mitochondrion has an outer membrane and a highly
folded inner membrane. As with ER, the folds of the inner membrane provide a
large surface area in a small space. Energy is produced on the inner folds.

Chloroplasts - Chloroplasts transform light energy directly into usable chemical
energy and store that energy in food molecules. These foods include sugars and
starches. Chloroplasts contain the molecule chlorophyll, a green pigment that
traps the energy from sunlight and gives plants their green color. The
chloroplast belongs to a group of plant organelles called plastids, which are
used for storage. Some plastids store starches or lipids, whereas others
contain pigments, molecules that give color.

Structures for Support and Locomotion:

The cytoskeleton is a network of thin, fibrous elements that act as a sort of
scaffold to provide support for organelles. It also helps maintain cell shape
in a manner similar to the way poles maintain the shape of a tent. The
cytoskeleton is usually composed of microtubules and microfilaments.
Microtubules are thin, hollow cylinders made of protein. Microfilaments are
thin, solid protein fibers. Microtubules and microfilaments make up most of the
sytoskeleton.

Cilia - Cilia are only contained in some cells. They are short, numerous,
hairlike projections out of the plasma membrane. Cilia tend to occur in large
numbers on a cell's surface, and their beating activity is usually coordinated.

Flagella - Flagella are longer projections that move with a whiplike motion.
Cells that have flagella only have one or two per cell. In single-celled
organisms, cilia and flagella are the major means of locomotion. Sperm cells of
animals and some plants move by means of flagella. Organisms that contain many
cells, including humans, have cilia that move fluids over a cell's surface,
rather than moving the cell itself.