|
Energy
is defined as a force that can do work. Energy
can exist in two main
forms:
|
Energy can exist in several forms, ranging from a stored form (potential energy) to a form that does something (kinetic energy) to a form that is wasted as heat. Molecules are
held together by an energy force. Breaking the bonds between atoms
releases that energy. Whether or not that bond energy does anything
depends on whether it can be captured and "put to work."
The body's job is to break food down so that cells can break down
some of the chemical bonds. Then that energy can be used to do
things (see below), before any left- over energy is finally lost as
heat.
Some
released energy escapes as heat.
| Released
energy is like steam rising over a stove pot. It disappears.
If energy is released all at once, much of it will escape as
heat.
But
even heat energy has its uses. Ever notice how frogs or fish are
sluggish on a cold day, but people can be just as active as
always. People make use of their "escaped" heat energy
to make chemical reactions run better and to make muscles contract
faster and stronger, even on cold days. Cold-blooded animals can't
do that. |
|
Why
do living systems need energy?
- to start
and control chemical reactions
- to transport
chemicals inside and outside of cells
- to make
proteins change shape and, as a result, change their function.
This kinetic
energy has to be delivered in small and controlled steps, so that
things happen in an orderly way.
Energy
containing nutrients are transported into cells, where the nutrients
are converted into an energy form readily used by the cell.
Energy-bearing nutrients have
to be brought to the cells by blood and other tissue fluids. These
nutrients then pass into cells. Glucose, a 6-carbon sugar
molecule, is the common breakdown product of table sugar, flour,
potatoes, and other starches. Even proteins and fats can get
broken down into glucoses. Once inside the cell, glucose
can be picked up by mitochondria where the energy in glucose is
released and trapped in a form that the cells can use. This
process is called
cellular respiration.
One More
Thing! Recent
research has revealed that mitochondria control death of cells. When
cells die, it seems that the cause arises because the membranes of
mitochondria loose their voltage charge, and this in turn causes a
release of certain proteins from mitochondria into the cytoplasm of
the cell. These proteins trigger a series of chemical reactions that
kill the cell.
Self Quiz
The organelle that breaks down
glucose to release and trap its energy is:
A.
Endoplasmic reticulum
B. Golgi apparatus
C. Mitochondria
D. Cell membrane
|
