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By the end of this section, you will be able to:
  • Define “energy”
  • Explain the difference between kinetic and potential energy
  • Discuss the concepts of free energy and activation energy
  • Describe endergonic and exergonic reactions

Energy is defined as the ability to do work. As you’ve learned, energy exists in different forms. For example, electrical energy, light energy, and heat energy are all different types of energy. While these are all familiar types of energy that one can see or feel, there is another type of energy that is much less tangible. This energy is associated with something as simple as an object held above the ground. In order to appreciate the way energy flows into and out of biological systems, it is important to understand more about the different types of energy that exist in the physical world.

Types of energy

When an object is in motion, there is energy associated with that object. In the example of an airplane in flight, there is a great deal of energy associated with the motion of the airplane. This is because moving objects are capable of enacting a change, or doing work. Think of a wrecking ball. Even a slow-moving wrecking ball can do a great deal of damage to other objects. However, a wrecking ball that is not in motion is incapable of performing work. Energy associated with objects in motion is called kinetic energy    . A speeding bullet, a walking person, the rapid movement of molecules in the air (which produces heat), and electromagnetic radiation like light all have kinetic energy.

Now what if that same motionless wrecking ball is lifted two stories above a car with a crane? If the suspended wrecking ball is unmoving, is there energy associated with it? The answer is yes. The suspended wrecking ball has energy associated with it that is fundamentally different from the kinetic energy of objects in motion. This form of energy results from the fact that there is the potential for the wrecking ball to do work. If it is released, indeed it would do work. Because this type of energy refers to the potential to do work, it is called potential energy    . Objects transfer their energy between kinetic and potential in the following way: As the wrecking ball hangs motionless, it has 0 kinetic and 100 percent potential energy. Once it is released, its kinetic energy begins to increase because it builds speed due to gravity. At the same time, as it nears the ground, it loses potential energy. Somewhere mid-fall it has 50 percent kinetic and 50 percent potential energy. Just before it hits the ground, the ball has nearly lost its potential energy and has near-maximal kinetic energy. Other examples of potential energy include the energy of water held behind a dam ( [link] ), or a person about to skydive out of an airplane.

The photo on the left shows water behind a dam. The photo on the right shows a waterfall.
Water behind a dam has potential energy. Moving water, such as in a waterfall or a rapidly flowing river, has kinetic energy. (credit “dam”: modification of work by "Pascal"/Flickr; credit “waterfall”: modification of work by Frank Gualtieri)

Questions & Answers

hetreothalism in fungi
Lekhram Reply
there are 3 trimester in human pregnancy
I don't know answer of this question can u help me
what is a cell
Fatima Reply
A cell is functional and structural unit of life.
what is genetic
Janet Reply
I join
what are the branchas of biology
Prisca Reply
zoology, ecology
genetics, microbiology,botany and embryology
what is a cell
Kulunbawi Reply
cell is smallest unit of life. cells are often cell the building blocks of life...
the first twenty element
Orapinega Reply
what are the characteristics of living things?
growth,respiration,nutrition,sensitivity, movement,irritability, excretion,death.
What is the difference between adaptation and competition in animals
Adeyemi Reply
What is biology
it is a natural science stadey about living things
Biology is the bronch of science which deals with the study of life is called biology
what is the x in 300 stands for?
Ogbudu Reply
the properties of life
Clarinda Reply
response to the environment, reproduction, homeostasis, growth,energy processing etc.....
what is reproduction
Reproduction is a fundamental feature of all known life,each individual organism exist as a result of re production.....or else Multiplying...
a complete virus particle known as
Darlington Reply
These are formed from identical protein subunitscalled capsomeres.
fabace family plant name
Pushpam Reply
in eukaryotes ...protein channel name which transport protein ...
Pushpam Reply
in bacteria ...chromosomal dna duplicate structure called
what is a prokaryotic cell and a eukaryotic cell
Matilda Reply
There are two types of cells. Eukaryotic and Prokaryotic cells. Prokaryotic cells don't have a nucleus or membrane enclosed organelles (little organs within that cell). They do however carry genetic material but it's not maintained in the nucleus. Prokaryotic cells are also one celled.
Prokaryotic cells are one celled (single celled).
Prokaryotic cells are Bacteria and Archea
Prokaryotic cells are smaller than Eukaryotic cells.
Eukaryotic cells are more complex. They are much bigger than Prokaryotic cells.
Eukaryotic cells have a nucleus and membrane bound organelles.
Eukaryotic cells are animals cells which also includes us.
Eukaryotic cells are also multicellular.
nice explaination
eukaryotic cells are individual cells .. but eukaryotes are multicellular organisms which consist of many different types of eukaryotic cells
also eukaryotic cells have mitochondria. prokaryotic cells do not
in prokaryotes only ribosomes are present... in eukaryotes mitochondria ...glogi bodies ..epidermis .....prokaryotes one envelop but eukaryotes compartment envelop....envelop mean membrane bound organelles......
prokaryotic cell are cells dat have no true nuclei i.e no cell membrane while eukaryotic cell are cell dat have true nuclei i.e have cell membrane
we have 46 pair of somatic cell and 23 pair of chromosomes in our body, pls can someone explain it to me. pls
Matilda Reply
we have 22 pairs of somatic chromosomes and one pair of sex chromosome
we have 23 pairs of chromosomes,22 pairs of somatic and one pair of sex chromosomes
23 chromosomes from dad & 23 chromosomes from mom 23 +23=46 total chromosomes
X & Y chromosomes are called sex cells, the very presence of a Y chromosome means the person is Male.
XX Female XY Male
If a Karyotype has more than 46 Chromosomes then nondisjunction occured. For example, having an extra chromosome 21 will cause Down Syndrome.

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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