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Cells are the Starting Point
All living organisms on Earth are divided in pieces called cells.
One Name, Many Types
Cells are the Starting Point
All living organisms on Earth are divided in pieces called cells. Cells are small
compartments that hold all of the biological equipment necessary to keep an organism
alive and successful on Earth.
There are many types of cells. In class, we worked with plant-like cells and animal-like
cells. We say animal-like because an animal type of cell could be anything from a tiny
microorganism to a nerve cell in your brain. Plant cells are easier to identify because they
have a protective structure called a cell wall. Plants have the wall; animals do not. Plants
also have organelles like the chloroplast (the things that make them green) or large waterfilled vacuoles.
Structures of the Cell
Cell Membrane
Both plant and animal cells have a cell membrane. Let's
look at the cell membrane and see how that membrane
keeps all of the pieces inside. When you think about a
membrane, imagine it is like a big plastic bag with
some tiny holes. That bag holds all of the cell pieces
and fluids inside the cell and keeps any nasty things
outside the cell. The holes are there to let some things
move in and out of the cell.
Cell Wall - What's it for?
While cell membranes might be around every cell, cell walls made of
cellulose are only found around plant cells. Cell walls are made of
specialized sugars called cellulose. Cellulose provides a protected
framework for a plant cell to survive. It's like taking a water balloon and
putting it in a cardboard box. The balloon is protected from the outside
world. Cellulose is called a structural carbohydrate (complex sugar)
because it is used in protection and support.
A cell wall is not a fortress around the delicate plant cell. There are small
holes in the wall that let nutrients and waste through.
Cytoplasm - Filling Fluid
Cytoplasm is the fluid that fills a cell. The cell organelles are suspended in the cytoplasm.
The fluid that makes up the cytoplasm in a cell does more than just suspend the
organelles. It distributes materials such as oxygen and food to different parts of the cell.
Cell Nucleus - Commanding the Cell
The cell nucleus acts like the brain of the cell. It helps control eating, movement, and
reproduction. If it happens in a cell, chances are the nucleus knows about it. The nucleus
is not always in the center of the cell. It will be a big dark spot somewhere in the middle of
all of the cytoplasm. You probably won't find it near the edge of a cell because that might
be a dangerous place for the nucleus to be. If you don't remember, the cytoplasm is the
fluid that fills cells.
The nuclear membrane surrounds the nucleus and all of its contents. The nuclear
membrane is similar to the cell membrane around the whole cell.
Mitochondria - Turning on the Powerhouse
Mitochondria are known as the powerhouses of the cell. They are organelles that act like
a digestive system that takes in nutrients, breaks them down, and
creates energy for the cell. A mitochondrion is shaped perfectly to
maximize its efforts.
Mitochondria are very small organelles. You might find cells with
several thousand mitochondria. The number depends on what the
cell needs to do. If the purpose of the cell is to transmit nerve
impulses, there will be fewer mitochondria than in a muscle cell that
needs loads of energy. If the cell feels it is not getting enough
energy to survive, more mitochondria can be created. Sometimes
they can even grow, move, and combine with other mitochondria,
depending on the cell's needs.
Chloroplasts - Show me the Green
Chloroplasts are the food producers of the cell. They are only found in
plant cells. Animal cells do not have chloroplasts. Every green plant you
see is working to convert the energy of the sun into sugars. Plants are the
basis of all life on Earth. They create sugars, and the byproduct of that
process is the oxygen that we breathe. That process happens in the
chloroplast. Mitochondria work in the opposite direction and break down
the sugars and nutrients that the cell receives.
Vacuoles - Storage Bins to the Cells
Vacuoles are storage bubbles found in cells. They are found in both animal and plant cells
but are much larger in plant cells. Vacuoles might store food or any variety of nutrients a
cell might need to survive. They can even store waste products so the rest of the cell is
protected from contamination. Eventually, those waste products would be sent out of the
cell.
Helping with Support
Vacuoles also play an important role in plant structure. Plants use cell walls to provide
support and surround cells. The size of that cell may still increase or decrease depending
on how much water is present. Plant cells do not shrink because of changes in the amount
of cytoplasm. Most of a plant cell's volume depends on the material in vacuoles.
Those vacuoles gain and lose water depending on how much water is available to the
plant. A drooping plant has lost much of its water and the vacuoles are shrinking. It still
maintains its basic structure because of the cell walls. When the plant finds a new source
of water, the vacuoles are refilled and the plant regains its structure.
Retrieved, adapted and modified from “Biology4Kids.com”
http://www.biology4kids.com/files/cell_main.html