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The left side of this diagram depicts energy being transferred from an ice cream cone to two boys riding bikes. The right side depicts a plant converting light energy into chemical energy: Light energy is represented by the sun, and the chemical energy is represented by a green leaf on a branch.
Shown are some examples of energy transferred and transformed from one system to another and from one form to another. The food we consume provides our cells with the energy required to carry out bodily functions, just as light energy provides plants with the means to create the chemical energy they need. (credit "ice cream": modification of work by D. Sharon Pruitt; credit "kids": modification of work by Max from Providence; credit "leaf": modification of work by Cory Zanker)

A living cell’s primary tasks of obtaining, transforming, and using energy to do work may seem simple. However, the second law of thermodynamics explains why these tasks are harder than they appear. All energy transfers and transformations are never completely efficient. In every energy transfer, some amount of energy is lost in a form that is unusable. In most cases, this form is heat energy. Thermodynamically, heat energy    is defined as the energy transferred from one system to another that is not work. For example, when a light bulb is turned on, some of the energy being converted from electrical energy into light energy is lost as heat energy. Likewise, some energy is lost as heat energy during cellular metabolic reactions.

An important concept in physical systems is that of order and disorder. The more energy that is lost by a system to its surroundings, the less ordered and more random the system is. Scientists refer to the measure of randomness or disorder within a system as entropy. High entropy means high disorder and low energy. Molecules and chemical reactions have varying entropy as well. For example, entropy increases as molecules at a high concentration in one place diffuse and spread out. The second law of thermodynamics says that energy will always be lost as heat in energy transfers or transformations.

Living things are highly ordered, requiring constant energy input to be maintained in a state of low entropy.

Potential and kinetic energy

When an object is in motion, there is energy associated with that object. Think of a wrecking ball. Even a slow-moving wrecking ball can do a great deal of damage to other objects. Energy associated with objects in motion is called kinetic energy    ( [link] ). A speeding bullet, a walking person, and the rapid movement of molecules in the air (which produces heat) all have kinetic energy.

Now what if that same motionless wrecking ball is lifted two stories above ground with a crane? If the suspended wrecking ball is unmoving, is there energy associated with it? The answer is yes. The energy that was required to lift the wrecking ball did not disappear, but is now stored in the wrecking ball by virtue of its position and the force of gravity acting on it. This type of energy is called potential energy    ( [link] ). If the ball were to fall, the potential energy would be transformed into kinetic energy until all of the potential energy was exhausted when the ball rested on the ground. Wrecking balls also swing like a pendulum; through the swing, there is a constant change of potential energy (highest at the top of the swing) to kinetic energy (highest at the bottom of the swing). Other examples of potential energy include the energy of water held behind a dam or a person about to skydive out of an airplane.

Questions & Answers

Species A has 12 pairs of chromosomes and Species B has 11 pairs of chromosomes. Explain what occurs during mitosis and during meiosis in the hybrid that allows normal development and growth from zygote to adult, but causes the adults to be sterile.
Christina Reply
Why does water move through a membrane?
Christina Reply
How many bones are in the human skeleton
Treasure Reply
203
Oyeleke
procce of digestion of proteins a long human alimentarycanal
Carson Reply
what are the properties of lipids?
Isiah Reply
They are: Fatty acids, fats, oils, waxes, phospholipid, glycolipids, steroids and some vitamins
Rachel
explain why a fresh water fish excrete ammonia
Leonard Reply
plz answer my question
Leonard
sorry i meant it has a nucleous unlike plant cells lol
Lailah
Ammonia is the end product of protein catabolism and is stored in the body of the fish in high concentrations relative to basal excretion rates. Ammonia, if allowed to accumulate, is toxic and is converted to less toxic compounds or excreted
Rachel
What are eukaryotic cells?
Nwosueke Reply
cell with no nucleous so not a plant cell
Lailah
eukaryotic cells are membrane bound organelles that have a membrane bound nucleus
ojeen
where does the cell get energy for active transport processes?
A'Kaysion Reply
IDK maybe glucose
Lailah
what is synapsis
Adepoju Reply
how many turns are required to make a molecule of sucrose in Calvin cycle
Amina Reply
why Calvin cycle occurs in stroma
Amina
why do humans enhale oxygen and exhale carbondioxide?
Maryam Reply
why do humans enhale oxygen and exhale carbondioxide? For the purpose of breaking down the food
dil
what is allele
uzoka Reply
process of protein synthesis
SANTOSH Reply
what is cell
Zulf Reply
a cell is a smallest basic, structural and functional unit of life that is capable of self replication
Lucas
why does a fresh water fish excrete ammonia
Leonard
plz answer my question
Leonard
Ammonia is a toxic colorless gas and when its inside the fish biological system is converted to a less toxic compound then excreted in the form of urea. However too much ammonia will kill the fish " Ammonia Poisoning " which is a very common disease among fish.
This
what is cytoplasm
uzoka Reply
cytoplasm is fluid of cell.
Deepak

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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