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The Cell The cell is the simpliest unit of life. All living
organism are composed of cells
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Each and every cell is composed of many different organelles.
All of these organelles play an important part or role in the
healthy function of the cell. Today we are looking at two specific
forms of cells, the plant and animal cell!
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A plant cell Plant cells are quite different from the cells of
the other eukaryotic organisms. Their distinctive features are: A
large central vacuole (enclosed by a membrane, the tonoplast),
which maintains the cell's rigidity and controls movement of
molecules between the cytosol and sap. A primary cell wall
containing cellulose, hemicellulose and pectin, deposited by the
protoplast on the outside of the cell membrane; this contrasts with
the cell walls of fungi, which contain chitin, and the cell
envelopes of prokaryotes, in which peptidoglycans are the main
structural molecules
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Plant cell contd The plasmodesmata, linking pores in the cell
wall that allow each plant cell to communicate with other adjacent
cells; this is different from the functionally analogous system of
gap junctions between animal cells. Plastids, especially
chloroplasts that contain chlorophyll, the pigment that gives
plants their green color and allows them to perform photosynthesis.
Higher plants, including conifers and flowering plants
(Angiospermae) lack the flagellae and centrioles that are present
in animal cells.
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The structure of a plant cell!
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An animal cell An animal cell is a form of eukaryotic cell that
makes up many tissues in animals. The animal cell is distinct from
other eukaryotes, most notably plant cells, as they lack cell walls
and chloroplasts, and they have smaller vacuoles. Due to the lack
of a rigid cell wall, animal cells can adopt a variety of shapes,
and a phagocytic cell can even engulf other structures. There are
many different cell types. For instance, there are approximately
210 distinct cell types in the adult human body
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The structure of an animal cell!
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Cell Structures! In each cell there are many and different
unique types of organelles. They are like miniature structures.
These structures all have different jobs to do and helps to keep
the cell in perfect form.
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The Cell Wall This structure is found only in plant cells and
is made from the polysaccharide Cellulose. Cellulose forms fibres
in a criss-cross pattern with spaces which allow the cell wall to
be permeable. Even very large molecules are allowed to pass though.
The cell wall promotes support and protection of the cell. It
encloses the cell membrane and protoplasm of the cell.
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The Cell Membrane The cell membrane or plasma membrane is very
thin and is made up mainly of protein and fat. It is found in both
plant and animal cells. It controls substances that enter and leave
the cell.
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Cytoplasm This is a clean or transparent, jelly-like liquid
consisting of the cells organelles suspended in it. 80% water and
20% dissolved substances. It supports organelles and
inclusions.
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Mitochondrion This organelle is often referred to as the power
house of the cell. The more energy a cell needs and use the more
mitochondrion it will have. It is rod-shape with smooth outer
membrane and dark, folded inner membrane. Contains respiratory
enzymes. Releases energy from food, during the process of
respiration.
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Mitochondrion Contd It has two membranes: a smooth outer
membrane and a highly folded inner membrane. Thus it contains two
compartments, the intermembrane space and the internal matrix
space. The enzymes that catalyze the reactions of respiration are
components of either the gellike matix or the inner mitochondrial
membrane. These enzymes couple the energy producing oxidation of
nutrients to the energy-requiring synthesis of ATP
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Mitochondrion
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Vacuoles These organelles are referred to as bubbles in cells.
It is a spaced surrounded by a membrane, called the vacuolar
membrane. It contains water, ingested materials, proteins, sugars
and minerals. The vacuole serves purpose to gather sugar and
minerals or waste products, this solution is called cell sap.
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Chloroplast These are plastids which contain the green pigment
chlorophyll. This pigment is needed by plants and plant-like
protists to make their food. Chloroplasts are found only in plant
cell.
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Nucleus This is a small, oval body which is enclosed by a
porous membrane called the nuclear membrane. It contains matter
called nucleoplasm. Within The nucleus there are long, thin
structures called chromosomes which store the information on the
features the an organism will inherit from its parent.
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Nucleus Contd Contains information which helps the ribosomes to
make proteins of the right kind. the nucleus is important in the
role of cell division in order for it to grow and reproduce.
Therefore without a nucleus the cell will not grow or reproduce and
will have a greatly reduced life span.
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Nucleus Contd The eukaryotic cells most conspicuous organelle,
is the repository of its genetic information. Within the nucleus,
the genetic information encoded by the DNA is transcribed/copied
into molecules of RNA Which, after extensive processing, are
transported to the cytoplasm where they direct the ribosomal
synthesis of proteins. Contains a dark-staining body known as the
nucleolus.
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Ribosomes These organelles are made of proteins and other
macromolecules. They are found either floating freely throughout
the cytoplasm or attached to the membranes of the endoplasmic
reticulum. Ribosomes attached to the ER sythesize proteins for
secretions, or release, from the cell for use by other cells.
Protein synthesis (putting substances together to make protein)
occurs on ribosomes. Unattached ribosomes in the cytoplasm
sythesize proteins that would be used in the cell.
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Endoplasmic Reticulum Is a network of membranes within the
cytoplasm (abbreviated as ER). The ER provide a place for the
attachment of enzymes. The spaces between the ER membranes seem to
serve as canals in the cytoplasm, through which materials are
transported. So materials are able to move all the way from the
nucleus to the outside of the cell through this canal system. There
is a Rough ER and a Smoothe ER
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Endoplasmic Reticulum Contd A large portion is called the rough
ER which is studded that are engaged in the sythesis of proteins.
The other is the smooth ER, which is devoided of ribosomes, is the
site of lipid synthsis. Many synthesized products are eventually
tranported to the Golgi apparatus.
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Centrioles Centrioles function during mitosis. Centrioles are
present in animal cells and in the body of some single celled
organisms.
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Microtubules Microtubules form a type of cellular skeleton.
They are very small tube-like structures that lie in parallel
bundles, often just outside the cell membrane. They are like a cell
skeleton that makes the cell more rigid.
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Lysosome The lysosome is a bag of digestive enzymes. It
attaches to and encloses materials brought into the cell. The
digestion then takes place inside the membranes of the lysosome.
The digested materials then pass through the lysosome membrane. The
enzymes remain inside, so they cannot digest the rest of the
cell.
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Golgi apparatus It is a specialized part of the ER. Its
function is the manufacture and export of materials from the cell.
From time to time one of the sacs will break off from the others
and migrate to the outside of the cell. This is one means by which
some of the manufactured products reach the outside of the
cell.
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Differences between a plant cell and an animal cell. Plant
Animal Usually round, square or rectangular Have a cell wall made
of cellulose Have chloroplast containing chlorophyll Have a large
permanent vacuole containing cell sap Stores food as starch grains
Have a great variety of shapes Have no cell wall No chloroplast or
chlorophyll Have many small temporary vacuoles whose contents vary
Stores food as glycogen granules
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Questions 1. What is the network of canals called that runs
through the cytoplasm? 2 What is the function of the lysosome? 3.
What is the function of the cell membrane? 4. How are microtubules
beneficial to certain cells?