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. The process of creating cell energy is known as cellular respiration. Most of
the chemical reactions involved in cellular respiration happen in the mitochondria. 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.
Mitochondria Structure
Mitochondria have two membranes (not
one as in other organelles). The outer
membrane covers the organelle and
contains it. The inner membrane folds over
many times (cristae). That folding
increases the surface area inside the
organelle. Many of the chemical reactions
happen on the inner membrane of the
mitochondria. The increased surface area
allows the small organelle to do as much
work as possible. If you have more room to
work, you can get more work done. Similar
surface area strategies are used by
microvilli in your intestinal cells. The fluid
inside of the mitochondria is called the
matrix.
Using Oxygen to Release Energy
How are mitochondria used in cellular respiration? The matrix is filled with water (H2O)
and proteins (enzymes). Those proteins take food molecules and combine them with
oxygen (O2). The mitochondria are the only place in the cell where oxygen can be
combined with the food molecules. After the oxygen is added, the material can be
digested. They are working organelles that keep the cell full of energy.
A mitochondrion may also be involved in controlling the concentration of calcium (Ca)
within the cell.
http://www.biology4kids.com/files/cell_mito.html 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.
Special Structures
We'll hit the high points for the structure of a
chloroplast. Two membranes contain and protect the
inner parts of the chloroplast. The stroma is an area
inside of the chloroplast where reactions occur and starches (sugars) are created.
One thylakoid stack is called a granum. The thylakoids have chlorophyll
molecules on their surface. That chlorophyll uses sunlight to create sugars. The
stacks of sacs are connected by stromal lamellae. The lamellae act like the
skeleton of the chloroplast, keeping all of the
sacs a safe distance from each other and
maximizing the efficiency of the organelle.
Making Food
The purpose of the chloroplast is to make
sugars and starches. They use a process
called photosynthesis to get the job done.
Photosynthesis is the process of a plant
taking energy from the Sun and creating
sugars. When the energy from the Sun hits a
chloroplast, chlorophyll uses that energy to
combine carbon dioxide (CO2) and water
(H2O). The molecular reactions create sugar
and oxygen (O2). Plants and animals then use the sugars (glucose) for food
and energy. Animals also use the oxygen to breathe.