1. How the Body Obtains and Uses Energy
Picture from:
How the Body Obtains and Uses Energy
Copyright PEER.tamu.edu

2. Turn to a Partner and Discuss:
Are you an energetic person?
When do you have the most energy?
What do you do when you need to get more energy?
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3. Energy Energy is all around you! You can hear energy as sound.
You can see energy as light.
And you can feel it as wind.
Tornado picture from:
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4. When do you use energy? You use energy when you hit a softball.
lift your book bag.
grow.
study.
do any activity.
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5. Why is energy important to our bodies?
Living organisms need energy for their bodies’ daily activities and processes.
Tiger Photo:
Gazelle Photo:
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6. Energy Conversions or Transformations
Energy can be changed from one form, or state, into another. Changes in the forms or states of energy are called energy conversions or transformations.
Ask students to look at the picture and tell how energy is being converted.
The potential (chemical) energy on the tip of the match is being converted into chemical energy of burning and heat or thermal energy and electromagnetic energy (light).
The process is started by mechanical energy (friction) of the match being converted into heat or thermal energy to start the fire.

7. Chemical Energy  Mechanical and Heat Energy
An Essential Energy Conversion
Our body converts starches, sugars, fats and even proteins (chemical energy) that we eat into energy for our bodies’ daily functions (mechanical and heat—or thermal—energy).
Ask the students to tell their favorite way of getting chemical energy… in other words, what is their favorite food?
Then ask them to think about how much exercise it would take them to use all of the energy gained from that food.
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Chemical Energy  Mechanical and Heat Energy

8. How the Body Obtains Energy
First, you consume energy in the form of foods. Foods are made of organic molecules.
The organic compounds in foods that can be used for energy are:
Carbohydrates
Fats
Proteins
Point out that organic molecules are made of Carbon, Hydrogen, Oxygen, and Nitrogen. They may also contain other elements like sulfur and phosphorous. If students have already learned this, then ask them to tell why the molecules pictured are called organic molecules.
Ask the students to tell what they think those molecules are used for in the body.
Discuss that Proteins are mainly used for building structures in the body like cells and organs. Proteins are usually not used for energy unless the body is very low in energy or that all of the body’s needs for building structures have been met.
Fat is also important for other reasons than obtaining energy. Fat helps the brain and nerves develop properly as well as helping the body absorb certain vitamins. Fat actually has more than 2x the amount of energy as carbohydrates and proteins.
Carbohydrates are primarily used for energy.
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9. During the digestion process, how does the body break down foods into smaller organic compounds?
The teeth first break down the food physically into smaller pieces. The movement of the stomach and intestines also help physically break the food.
Proteins are broken down chemically by pepsin in the stomach into amino acids.
Carbohydrates are broken down chemically into sugars (monosaccharides) by enzymes found in saliva in the mouth and by enzymes in the small intestine.
Ask the students to trace the path of food through the digestive system as a review.
Amino acids are either used to synthesize proteins and other biomolecules, or oxidized to urea and carbon dioxide as a source of energy.
Fats are broken down into fatty acids in the small intestines by bile from the liver.

10. These smaller molecules are transported into body cells and then go through several chemical processes that break the molecular bonds to produce ATP, a primary storage form and source of energy in the body.
These chemical processes occur in the cytoplasm and mitochondria of the cells.
Mitochondria
Cytoplasm
ATP stands for Adenosine triphosphate. ATP serves as the immediate source of energy for the mechanical work performed by muscle. By virtue of its energy-rich pyrophosphate bonds, ATP serves as a link between sources of energy available to a living system and the chemical and mechanical work which is associated with growth, reproduction, and maintenance of living substance. For this reason, it has been referred to as the storehouse of energy of living systems.
Cell picture from:
Simplified Glycolysis and Krebs Cycle from:
The link on this slide it to
Which contains a detailed lesson on this topic explaining the chemical processes only briefly mentioned here.

11. Mitochondria (plural of mitochondrion) are the  organelles that cells use as their energy factories. Think of them as the cell's way of recharging its battery.
Artists Mitochondria picture from:
Micrograph picture of mitochondria from:
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.
An artist’s representation of a mitochondrion
An electron micrograph of a mitochondrion
A mitochondrion is an oval bag that is filled with membranes. Mitochondria are so small that you can only see them with the high-power magnification of an electron micrograph.

12. Stop and Think: What is an energy conversion or transformation?
What energy conversion is essential for the human body?
Summarize how humans get their energy from food. Be sure to include the structures in the body that are responsible for this process.