Download Energy and Work - LeRoy Eyring Center For Solid State Science

Energy and You
Our bodies are complex biological machines that use food as fuel for energy.
Energy and Work
We don’t know what energy IS, we only know what energy DOES. Energy is the ability to work.
Work is done when a force makes something move. A force is just a push or a pull. If a force makes
something move, work has been done and that takes energy. Different kinds of work are done by
different kinds of energy. Energy can be stored, it can move from one place to another and it can change
from one kind of energy to another.
Energy in Sunlight
Solar radiation, or sunlight, is the most abundant kind of energy on Earth. In five minutes,
sunlight gives Earth as much energy as the United States uses in an entire year! Without sunlight, life on
earth would not be possible.
Energy and Life
Living organisms need a constant stream of raw materials and energy. Life is a very demanding
process! It requires a lot of energy, delivered under just the right conditions and used to perform many
kinds of work on many different levels, all the way down to molecules and atoms.
Energy in the Food Chain
Plants are the first link in the food chain. They build their own nutrients from substances in the air
and soil, using energy from sunlight to do the work. Plants use photosynthesis to convert sunlight into
chemical energy that is stored in plant tissue containing carbohydrates, proteins and fats. This energy is
passed on to herbivores (animals that eat only plants), carnivores (animals that eat only meat) and
omnivores (animals that eat both). Unlike plants, animals must consume all their nutrients and digest
them for energy. When we eat plants or animals, we get energy from them that was once the energy in
sunlight!
Energy in Chemical Bonds
Carbohydrates, proteins and fats are organic molecules in plants and animals made from different
kinds of atoms, such as carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. In molecules, these
atoms are held together by strong forces called chemical bonds. Chemical bonds are like springs that hold
the atoms together.
A spring stores energy when it is compressed or stretched. A vibrating spring also stores energy
because it is moving between being compressed and being stretched.
In a molecule of food, the atoms are vibrating back & forth very quickly, so the chemical bonds
holding them together store lots of energy. When a chemical bond is broken, the food molecule breaks
apart. The energy that was stored in the chemical bond can be released as heat, or it can be used to do
some kind of work, or it can be stored in the chemical bonds of other newly formed molecules. When
chemical bonds are broken or formed, it is called a chemical reaction.
Combustion
Chemical bonds can be broken by combustion, or burning. Oxygen in the air reacts with the
molecules in plant tissue, breaking them into smaller molecules such as carbon dioxide and water. When
those bonds are broken, the energy stored in them is released as heat, producing fire. Animal tissue can
also burn, especially fats, which store lots of energy. Old fashioned oil lamps burn animal fats that are
liquid at room temperature. Kitchen grease fires can be very dangerous because lots of energy can be
released quickly through combustion.
David P. Wright, [email protected], LeRoy Eyring Center for Solid State Science, School of Materials, Arizona State University, Tempe
Metabolism
All the chemical reactions that happen inside an organism contribute to its metabolism. These
reactions provide energy and material for all the processes of life such as breathing, blood flow, digestion,
growth, control of body temperature, healing and reproduction.
Some of these reactions break down big molecules into smaller ones. Digestion breaks down food
molecules to release energy to the body and provide simpler building blocks for tissue growth.
Some of these reactions build up small molecules into big ones. Proteins are made from small
amino acids linked together in long chains. Muscle tissue has lots of protein. Bodybuilders eat lots of
protein and extra amino acids to help their muscles grow.
Respiration
Chemical bonds can be broken by respiration, or breathing. When animals breathe, they inhale
oxygen and exhale carbon dioxide. This is called aerobic respiration, because air is involved. Overall,
breathing is similar to combustion.
Plants also respire, but they take in carbon dioxide and release oxygen, the reverse of what animals
do. Animals use the oxygen that plants produce and plants use the carbon dioxide animals produce.
Anaerobic respiration is another kind of respiration that breaks down molecules to release energy,
but without air. Some kinds of microscopic yeast and bacteria live entirely without air because they use
anaerobic respiration to get their energy and raw materials for life.
Digestion
A well-balanced meal contains protein, carbohydrates and essential fats. Digestion is a complex
process that breaks down these substances into simple molecules and releases the stored energy so it can
be used by the body. Digestion starts in the mouth and continues as food moves through the stomach and
intestines. Digestion provides raw materials that can be used all over the body to build new tissues. The
energy released from food during digestion is used to do some kind of work or stored as fat, depending on
how much energy is needed and how much food is consumed.
Digestion requires a lot of energy because it takes a lot of work to break down food into simple
molecules. However, food contains more energy than is needed to digest it, so digestion overall provides
more energy than it requires.
David P. Wright, [email protected], LeRoy Eyring Center for Solid State Science, School of Materials, Arizona State University, Tempe