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7.12EF Functions of a Cell
Organisms and Environment
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A Close Look Into Cells
Lexile 1050L
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What are cells? Cells are the smallest units that
carry out all of the activities of life in organisms.
All living organism are made up of one or more
cells. New cells arise completely out of cell
division. Cells are similar to humans in that they
feed, excrete, and absorb. Humans eat, because
they need energy. Cells too have an energy
source. Humans can absorb Vitamin D from the
sun’s ray through the skin for nutrients. This is
similar to how cells allow certain ions into their
system for nutrients. Some organisms are
composed of a single cell, like bacteria or some
algae, and they can only be seen through the
use of a microscope. Other organisms are
composed of multiple cells, such as humans,
animals, trees, and flowers. These multicellular
organisms can be seen without a microscope.
Blood Cells
A microscope is an instrument used by scientists to study cells and other
microscopic organisms. It is similar to a magnifying glass. It has only one
lens. The first crude microscope was designed by a Dutch maker, Zacharias
Janssen, in 1590. He simply placed two magnifying glasses together in a
tube creating the first compound microscopes. Although it would magnify
an image, but it was not always clear or sharp. By the mid 1600s, another
Dutch scientist, Anton Van Leeuwenhoek, made a simple microscope utilizing
tiny glass bead for a lens. This new lens allowed him to see an image up to
270 times larger than its actual size. Anton reported being able to see
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7.12EF Functions of a Cell
Reading Science!
Organisms and Environment
things in pond water that no one had ever imagined before. The microscope
that is used in studying life science is a compound light microscope. Simply,
this instrument allows light to pass through an object, and then through two
or more lenses. Since the lenses in the microscope are convex, it enlarges the
image and bends the light towards your eye. It also has an eyepiece lens
with its power of 10X, or it has the power to make an image of an object ten
times larger than its actual size.
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In 1665, when the microscope was improved, an English scientist, Robert
Hooke, examined a very thin slice of cork made from a tree and looked at it
under a microscope. Hooke observed what appeared to be empty, box-like
structures which reminded him of a prison cell. Hence, the name, cell.
However, all cells do not look like the square shape of a plant cell. Human,
bacterial, fungal, and algal cells all take on different shapes. As cells were
studied over time, different observations and conclusions were made by
numerous scientists. Together, their explanations became known as the cell
theory, one of the major theories in science. The major ideas of cell theory
include: 1) All organisms are made up of one or more cells; 2) Cells are the
basic units of structure and function in all organisms; and, 3) All cells come
from cells that already exist. Today, cell theory is the basis scientists use to
study the parts of cells, how they are organized, reproduce and change
through time.
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Every cell of an organism, as small as they are, is made up of even smaller
parts known as organelles. What does the name “organelles” imply? Just as
in your body, there are many different organs, each with a unique function,
but nevertheless in concert to sustain life. So it is with an organelle. Each
organelle performs a distinctive function. Part of their uniqueness is that
plant organelles are different than organelles found in animals. Organelles
perform the distinctive work of the cell.
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7.12EF Functions of a Cell
Reading Science!
Organisms and Environment
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Scientists have found that cells are organized in two different groups:
prokaryotic and eukaryotic. Prokaryotic are cells have no membrane around
their nuclear material. An example of prokaryotic is found in bacteria and
cells that form pond scum. Eukaryotic cells, as found in animal and plant
cells, have a nucleus and a membrane around it. There are some key parts
common to most eukaryotic cells: cell membrane, cell wall, nucleus, and
cytoplasm.
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A cell membrane covers the outside of the cell by separating the interior of
the cell from its surrounding environment. One of its purposes is to regulate
what enters and leaves the cell. Similar to a small manufacturing business,
materials needed for assembling a specific product within the establishment
are brought into the facility, constructed, and once fabricated, products are
shipped out. The cell membrane also allows food and oxygen (nutrients) to
be absorbed into the cell through the membrane while excreted waste
products are expelled through the cell membrane. Another beneficial
purpose of the cell membrane is to maintain a chemical balance between
materials inside and outside the cell. In organisms such as plants, algae, and
some bacteria, the cell membrane is surrounded by a cell wall. The cell wall
helps to protect and support the cell. The structure is made of bundles of
tough cellulose fibers and other materials made by the cell. Together with all
the cell walls, it provides structure to whole organism.
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The nucleus, “the brain,” is a structure that directs all the activities of the cell.
It is like the central control center, or the brain, of the cell. Its role is similar to
a police officer who is responsible for safely directing traffic at a busy
intersection. The nucleus is the largest organelle in the cytoplasm of a
eukaryotic cell. Materials enter and leave through openings in the
membrane. The nucleus is separated from the cytoplasm. It contains
genetic blueprints for the functions of the cells in the form of long strands
called chromatin. Proteins and the chemical that controls the activities of
the cell, DNA, make up the chromatin. When a cell begins to divide, the
strands of chromatin begin to thicken and take on the form of
chromosomes. Chromosomes are found in the nucleus and contain DNA,
our genetic make up.
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7.12EF Functions of a Cell
Reading Science!
Organisms and Environment
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Cytoplasm is gel-like material that fills the cell. It is found between the cell
membrane and the nucleus. Organelles move about freely in the
cytoplasm and other cell activity occurs here. This gel-like material is inside
the cell membrane and outside the nucleus and is constantly moving.
Unlike a gelatin dessert, cytoplasm never solidifies.
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Within the cytoplasm’s structure of eukaryotic or animal cells are
organelles. Each has a designated job or jobs to serve that is essential for
the overall survival of the cell. Similar to a place of employment, each
employee has a particular task to perform in order for the business to be
financially successful. So it is with the responsibilities of the tasks assigned
to a cell which includes, but is not limited to, obtaining energy from food,
moving waste to be expelled from the cell, or storing material. Most
organelles are surrounded by membranes.
10 Endoplasmic reticulum (ER) is a complex series of folded membranes in the
cytoplasm of the cell that extends from the nucleus to the cell membrane
and allows for the passage and the processing of material throughout the
cell. Think of this membrane as a train in an airport which moves people
and their luggage from one terminal to the next. The ER takes up a lot of
space within some cells. It extends from the nucleus to the cell membrane.
One chemical that takes part in virtually every cell activity is protein which
is found in the cell membrane. Other proteins are needed within the cell so
that chemical reactions can take place in the cytoplasm. The job of the
ribosome is to make protein needed for the sole purpose of creating
chemical reactions. This organelle receives its orders from the hereditary
material of the nucleus as to how, when, and what order to make a specific
protein. Ribosomes can be found in two areas: freely floating in the
cytoplasm or attached to the endoplasmic reticulum.
11 Golgi bodies package materials and move them to the outside of the cell.
This process is easily seen in a production corporation. When a purchase is
made in business, product are produced, packaged, and moved to loading
docks to be carried away. In cells, structures called golgi bodies are stacks
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Reading Science!
7.12EF Functions of a Cell
Organisms and Environment
of flattened membrane-covered sacs that look like a stack of plates. Their
job is to package proteins into small membrane bound vessels and move
proteins to the outside of the cell. This packaging process allows the
material processed by the golgi to be transported around the cell.
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An active cell also constantly produces waste products. In the cytoplasm,
organelles called lysosomes contain digestive chemicals that aid in
breaking down food, cell waste, and worn-out organelles. Lysosomes also
recycle substances inside the cell. When a cell dies, chemicals in the
lysosomes quickly break down the cell. In a healthy cell, the membrane
around lysosome keeps the chemicals in the organelles itself from breaking
down the cell, in essence, from self-destructing.
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What is totally mind-boggling is that the plant cell has all the organelles as
an animal cell plus two more. The major difference is that plant cells have a
cell wall and chloroplasts. Another major difference is that a plant can
make its own food. These organelles contain a chemical known as
chlorophyll, which is a green pigment that traps sunlight and converts it
into a form of sugar which produces energy. It uses sunlight, water and CO2
to produce O2. This process is known as photosynthesis.
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All of these specific cells are not just thrown together. Each has a special
purpose and function. The cells within your own body have a specific
purpose. For example, you would not want to have a liver cell in your leg
muscle or a stomach muscle in your brain. All common cells are grouped
together to form specific tissue. Tissue is a group of similar cells that
perform a similar purpose. Tissue would then join together with different
tissue to form an organ. An organ is a structure that is made up of two or
more different types of tissue that work together to form an organ. That’s
miraculous for a cell to have that much power and control, even if it is the
smallest unit of life!
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