Functions of Organelles
Cells Cells are the smallest unit of living matter. They carry
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out complex chemical reactions. Some reactions make substances
needed by the cell. For example, most people have cells that make a
dark substance called melanin. Melanin clusters around the nucleus
to protect the DNA from sun damage. Kidney cells make a chemical
that is released when blood oxygen levels are low. This chemical
triggers cells in your bones to make more red blood cells to transport
more oxygen to the body tissues.
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Other chemical reactions break things apart. Cells in the spleen
carry out reactions that break down old red blood cells. Other cells
in your body produce chemicals that help break apart parasites.
Usually, you have very few of these cells. If high levels of these cells
are found in your body, it suggests that you have a parasite infection.
Organelles Many chemicals take part in these reactions, and
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they must be carefully regulated. Many cells have compartments
called organelles that separate reactions and perform different jobs.
There are many types of organelles.
In multicellular organisms, different kinds of cells carry out different
jobs. Skeletal muscle cells help otters to swim. Fat cells help
keep polar bears warm. Sweat glands help cool you on a hot day.
Cells that perform different functions may have different types of
organelles and different numbers of organelles.
Nucleus The nucleus is an organelle that directs the cell’s activities.
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It contains DNA, the cell’s operating instructions. DNA stores
information that is passed along to other cells. It is coded information
that directs how a living thing will grow and work.
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The nucleus is usually a large round organelle. It is easily visible
under the microscope. The nucleus contains holes, or pores. Molecules
exit the pores and affect what the cell is doing.
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Many cells have one large nucleus, but not all cells. Some of
your muscle cells are very long, and each cell contains many nuclei.
In fat cells, much of the interior space is occupied by a big blob of
fat stored inside a membrane. In these cells, called adipocytes, the
membrane is squished off to the side of the cell.
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Mitochondria All cells need energy to stay alive. Energy
comes in different forms. The sun that warms your skin is one type
of energy. The wind that blows your hair about is another type
of energy. The electricity that lights and heats your home is yet
another type of energy.
Cells cannot use just any type of energy, so cells have mitochondria.
Mitochondria are organelles that change chemical energy
from food into a form of energy that cells can use. They are shaped
liked jellybeans. Your muscle cells use a lot of energy, so they have
thousands of mitochondria. In fact, the more you use your muscles,
the more mitochondria you have. Skin cells do not use as much
energy, so they have fewer mitochondria.
Chloroplasts You probably eat several times a day, but have
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you ever seen a plant eat? Plants have some organelles that animal
cells do not have. And these organelles help plants to do things that
animals cannot do.
A major difference between plant and animal cells is that plants
have chloroplasts. Chloroplasts contain pigments give plants their
green color. Chloroplasts use energy from sunlight to turn water
and carbon dioxide into sugar and oxygen. This means that plants
make their own food from sunlight. Imagine how handy it would
be if you were able to snack on sunlight.
Animals depend on plants for life. Plants provide the oxygen
that we and other animals breathe, and they provide the food we
eat. Even animals that eat only meat depend on plants. For example,
snakes and hawks eat mice, but mice eat plants.