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Nearly all chemical reactions occur at a faster rate at higher temperatures. Recall that kinetic energy is the energy of matter in motion. The kinetic energy of subatomic particles increases in response to increases in thermal energy. The higher the temperature, the faster the particles move, and the more likely they are to come in contact and react.

Concentration and pressure

If just a few people are dancing at a club, they are unlikely to step on each other’s toes. But as more and more people get up to dance—especially if the music is fast—collisions are likely to occur. It is the same with chemical reactions: the more particles present within a given space, the more likely those particles are to bump into one another. This means that chemists can speed up chemical reactions not only by increasing the concentration    of particles—the number of particles in the space—but also by decreasing the volume of the space, which would correspondingly increase the pressure. If there were 100 dancers in that club, and the manager abruptly moved the party to a room half the size, the concentration of the dancers would double in the new space, and the likelihood of collisions would increase accordingly.

Enzymes and other catalysts

For two chemicals in nature to react with each other they first have to come into contact, and this occurs through random collisions. Because heat helps increase the kinetic energy of atoms, ions, and molecules, it promotes their collision. But in the body, extremely high heat—such as a very high fever—can damage body cells and be life-threatening. On the other hand, normal body temperature is not high enough to promote the chemical reactions that sustain life. That is where catalysts come in.

In chemistry, a catalyst    is a substance that increases the rate of a chemical reaction without itself undergoing any change. You can think of a catalyst as a chemical change agent. They help increase the rate and force at which atoms, ions, and molecules collide, thereby increasing the probability that their valence shell electrons will interact.

The most important catalysts in the human body are enzymes. An enzyme    is a catalyst composed of protein or ribonucleic acid (RNA), both of which will be discussed later in this chapter. Like all catalysts, enzymes work by lowering the level of energy that needs to be invested in a chemical reaction. A chemical reaction’s activation energy    is the “threshold” level of energy needed to break the bonds in the reactants. Once those bonds are broken, new arrangements can form. Without an enzyme to act as a catalyst, a much larger investment of energy is needed to ignite a chemical reaction ( [link] ).


The left panel shows a graph of energy versus progress of reaction in the absence of enzymes. The right panel shows the graph in the presence of enzymes.
Enzymes decrease the activation energy required for a given chemical reaction to occur. (a) Without an enzyme, the energy input needed for a reaction to begin is high. (b) With the help of an enzyme, less energy is needed for a reaction to begin.

Enzymes are critical to the body’s healthy functioning. They assist, for example, with the breakdown of food and its conversion to energy. In fact, most of the chemical reactions in the body are facilitated by enzymes.

Chapter review

Chemical reactions, in which chemical bonds are broken and formed, require an initial investment of energy. Kinetic energy, the energy of matter in motion, fuels the collisions of atoms, ions, and molecules that are necessary if their old bonds are to break and new ones to form. All molecules store potential energy, which is released when their bonds are broken.

Four forms of energy essential to human functioning are: chemical energy, which is stored and released as chemical bonds are formed and broken; mechanical energy, which directly powers physical activity; radiant energy, emitted as waves such as in sunlight; and electrical energy, the power of moving electrons.

Chemical reactions begin with reactants and end with products. Synthesis reactions bond reactants together, a process that requires energy, whereas decomposition reactions break the bonds within a reactant and thereby release energy. In exchange reactions, bonds are both broken and formed, and energy is exchanged.

The rate at which chemical reactions occur is influenced by several properties of the reactants: temperature, concentration and pressure, and the presence or absence of a catalyst. An enzyme is a catalytic protein that speeds up chemical reactions in the human body.

Questions & Answers

What is the role of Astrocytes in the blood brain barrier
Chilufya Reply
for cell to cell communications
5. Discuss thoroughly the renal regulation of acid-base balance in the body with the illustration of conservation of bicarbonate ion in the kidney
Jonathan Reply
What is anatomy
Tiamiyu Reply
anatomy is the study of the different organs of the body being internal and external organ
is't possible for non-identical twins to have different father ? ?
ANATOMY is the scientific study of the structure of human or animal bodies.
Anatomy is the branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts.
anatomy is the branch of science that duty with the study structure of the human and living organisms.
anatomy    is the scientific study of the body’s structures.
it is possible for non-identical twins to have different fathers. (yes)
examples of lymph nodes
Arimpa Reply
Clusters of lymph nodes are found in the neck, axilla (underarm), chest, abdomen, and groin. For example, there are about 20-40 lymph nodes in the axilla. Also called lymph gland. Anatomy of the lymph system, showing the lymph vessels and lymph organs including lymph nodes, tonsils, thymus, spleen,
Excellent 😊
in part of body where did we get medulla
Olawale Reply
Are you referring to the medulla oblongata? In which case, this is a part of the brain, located at the brain stem. It controls a lot of our unconscious behaviors such as motor coordination, breathing, etc.. But medulla generally refers to an innermost structure, so it can be found in hair or kidneys
that is the little brain piece behind your brain. like next to the stem.
How does blood circulate in the upper limbs
Mary Reply
From the aortic arch, blood is supplied to the brain via the R and L carotid arteries. To supply the upper limbs, blood goes to the R and L subclavian arteries, axillary, radial/ulnar, palmar and carpal arteries.
describe the muscles found in the heart
Atotwe Reply
thank you very much
asalamu aleikum
waalekum salam
types of connective tissues?
the muscle found in the body is myocardial muscles
what is a muscular system and details about it
Jackson Reply
what is the type of homones responseble for blenking of eyes
Moses Reply
what are the functions of cell?
Keyirangzile Reply
how does the femur act as a lever?
Mutoni Reply
what is stumac
Abdussalam Reply
what is a joint
where two or more bones articulate
What is phagocytosis
Mohamed Reply
Phagocytosis, process by which certain living cells called phagocyte
It is the process that is carried out by the immune system of the body, that certain specialized immune cells (macrophages, Nks, dendritic cells, etc) that engulf and neutralize the foreign substances that invades the body.
So that they can be predicate out of the body.
phagocytosis is the process by which living cell or yh plasma membrane engulf large molecules into it internal environment ... it also known as food feeding
all that you are say what does it mean?
simply is the way the immune system fights foreign bodies by engulfing them..
by the help of the immune cells...
The process by which a cell engulfs particles such as bacteria, other microorganisms, debris of dead cell.e.g: neutrophils and monocytes (types of white blood cells)
what are the six types of connective tissues
Athieno Reply
loose and dense , cartilage and bone , blood and lymph
there is 4 types of tissue in the body! is that what you want to know? epithelial = muscle= connective = nervous =
describe the structure of the liver
Atwebembeire Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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