Cells are important for everything that all living things
do. When we run and play, our movements are caused by muscle
cells and nerve cells working together. When we speak, get
an idea or decide what to say to somebody, brain cells are
working. When we digest our food, cells in our mouth, stomach,
and intestines are doing their jobs. Our beating heart, breathing,
eyesight, hearing, feeling and even sleeping all require cells.
All plants and animals are made of cells, and different kinds
of cells perform special types of work. Cells in the leaves
of green plants use sunshine, water and carbon dioxide in
the air as food to help the plants grow. Cells also produce
fish scales and bird feathers. Yeast cells make bread rise
before it is baked, and bacterial cells can make us sick,
help clean up oil spills and turn milk into yogurt.
Cells do many more things than the largest factory on earth,
yet most of them are too small to see without a microscope.
There are about 100 trillion cells in your body. This is 200
times greater than the number of stars in the Milky Way galaxy.
If every cell in your body were the size of a small drop of
water you would be 20 miles tall, and your waist would be
as big around as your house. As it is, most cells are so small
that several hundred could sit on the head of a pin without
lying on top of each other. A few unusual cells are very large
though. For example, the yellow part of a chickens egg
is one cell, and some nerve cells in the giant squid are several
yards long. In the human body, there are 252 different kinds
of cells. Each of these performs particular jobs in particular
organs of our body. For example, our blood contains more than
one dozen different kinds of cells. Some blood cells carry
oxygen throughout the body, some form blot clots when we get
cut, and others protect us from infections and diseases.
Scientists who study how cells work are called cell biologists.
Here are some of the things they have learned. Particular
jobs inside a cell are done by tiny cell parts called organelles
which means little organs. One organelle called
the mitochondrion uses energy in the food we eat to make chemical
fuel needed to keep the cell alive and working well. One cell
contains hundreds of mitochondria. Another organelle called
a ribosome manufactures thousands of different proteins. Proteins
are the chemical workhorses for the cell. They make our muscles
contract, allow us to think and form communication networks
between cells. One cell contains thousands of ribosomes. Organelles
called microtubules are like tiny soda straws inside the cell.
Like bones in our body, they form a mini-skeleton that gives
a cell its shape. The largest organelle is the nucleus. In
humans the nucleus contains two copies each of about 30,000
genes, one copy from our mother and the other from our father.
Genes carry chemical information that makes a tree a tree
and a human a human. Genes determine the color of our eyes
and our hair. They may also help give us our personalities,
but just as important for this are our experiences at home,
in school, with friends and while reading books.
One final thing about cells that is important to remember
is that every person in the world began life as one single
cell that grew and divided many times to make the trillions
of cells in our bodies. In this way and in many other ways,
we are all alike.
for your question,
Aubie and Dr. Bradley