Transcript Parts of the Cell - WBR Teacher Moodle

GLE 2; Grade 7
Parts of the Cell
http://www.biology4kids.com/files/cell_main.html
All living organisms on Earth are divided in pieces called cells. There are
smaller pieces to cells that include proteins and organelles. There are
also larger pieces called tissues and systems. 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 biology class, you will usually work 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 made of cellulose. Plants
have the wall; animals do not. Plants also have organelles like the
chloroplast (the things that make them green) or large water-filled
vacuoles.
Cell Membranes
We have been talking about cells being a unit of organization in biology. 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.
Cell walls also help a plant keep its shape. While they
do protect the cells, cell walls and cellulose also allow
plants to grow to great heights. While you have a
skeleton to hold you up, a 100-foot tall redwood tree
does not. It uses the strong cell walls to maintain its
shape. For smaller plants, cell walls are slightly
elastic. Wind can push them over and then they
bounce back. Big redwoods need strength in high
winds and sway very little (except at the top).
Cytoplasm - Filling Fluid
Cytoplasm is the fluid that fills a cell. Scientists used to call the fluid
protoplasm. Early on, they didn't know about the many different types of fluids
in the cell. There is special fluid in the mitochondria, endoplasmic reticulum,
Golgi apparatus, and nucleus. The only two 'plasms' left are cytoplasm (the
fluid in the cell also called cytosol) and nucleoplasm (the fluid in the
nucleus). Each of those fluids has a very different composition.
The cell organelles are suspended in the cytosol. You will learn that the
microfilaments and microtubules set up a "skeleton" of the cell and the cytosol
fills the spaces. The cytoplasm has many different molecules dissolved in
solution. You'll find enzymes, fatty acids, sugars, and amino acids that are
used to keep the cell working. Waste products are also dissolved before they
are taken in by vacuoles or sent out 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
(cytosol). 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.
When the cell is in a resting state there is something
called chromatin in the nucleus. Chromatin is made of
DNA, RNA, and nuclear proteins. DNA and RNA are
the nucleic acids inside of the cell. When the cell is
going to divide, the chromatin becomes very compact.
It condenses. When the chromatin comes together,
you can see the chromosomes. You will also find the
nucleolus inside of the nucleus. When you look
through a microscope, it looks like a nucleus inside of
the nucleus. It is made of RNA and protein. It does
not have much DNA at all.
Chloroplasts - Show me the Green
Chloroplasts are the food producers of the cell. They are only found in
plant cells and some protists. 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.
Chromosomes - Pull up Those Genes
Chromosomes are the things that make organisms what they are. They
carry all of the information used to help a cell grow, thrive, and reproduce.
Chromosomes are made up of DNA. Segments of DNA in specific patterns
are called genes. Your genes make you who you are. You will find the
chromosomes and genetic material in the nucleus of a cell. In prokaryotes,
DNA floats in the cytoplasm in an area called the nucleoid.
Endoplasmic Reticulum - Wrapping it Up
Another organelle in the cell is the endoplasmic
reticulum (ER). While the function of the nucleus is
to act as the cell brain, the ER functions as a
packaging system. It does not work alone. The
ER works closely with the Golgi apparatus,
ribososmes, RNA, mRNA, and tRNA. It creates a
network of membranes found through the whole
cell. The ER may also look different from cell to
cell, depending on the cell's function.
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.
The structure of vacuoles is fairly simple. There is a membrane that surrounds a mass of fluid. In that
fluid are nutrients or waste products. Plants may also use vacuoles to store water. Those tiny water bags
help to support the plant. They are closely related to objects called vesicles that are found throughout
the cell.
In plant cells, the vacuoles are much larger than in animal cells. When a plant cell has stopped growing,
there is usually one very large vacuole. Sometimes that vacuole can take up more than half of the cell's
volume. The vacuole holds large amounts of water or food. Don't forge that vacuoles can also hold the
plant waste products. Those waste products are slowly broken into small pieces that cannot hurt the cell.
Vacuoles hold onto things that the cell might need, just like a backpack.
Lysosomes - Little Enzyme Packages
You will find organelles called lysosomes in
nearly every animal-like eukaryotic cell.
Lysosomes hold enzymes that were created
by the cell. The purpose of the lysosome is to
digest things. They might be used to digest
food or break down the cell when it dies. What
creates a lysosome? You'll have to visit the
Golgi complex for that answer.
A lysosome is basically a specialized vesicle
that holds a variety of enzymes. The enzyme
proteins are first created in the rough
endoplasmic reticulum. Those proteins are
packaged in a vesicle and sent to the Golgi
apparatus. The Golgi then does its final work
to create the digestive enzymes and pinches
off a small, very specific vesicle. That vesicle is
a lysosome. From there the lysosomes float in
the cytoplasm until they are needed.
Lysosomes are single-membrane organelles.