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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 metabolism
fred Reply
Chemical reaction that takes in place in the cell of a living organism that includes anabolism and Catobolism.
metabolic chemical reaction is of two types, anabolism and catabolism. The break down of larger molecules into smaller molecules is called catabolism.
Metabolism is the chemical reaction that includes anabolism and catabolism
Anabolism is the chemical reaction that combines all the smaller quantities to make large
Catabolism is the chemical process that breaks larger quantities into small
what's abdominal police?
hydrochloric acid is the stomach police
its the stomach omentum
description of the ears
Nana Reply
which component of mucus allows it to maintain local level of hydration
Loriann Reply
can the teeth be classify under bones?
Ojaga Reply
Bony prominents
What is the largest muscle in the lower leg
Gwen Reply
what's a nervous system
Dante Reply
Is a the group of neurons and glial cells that work together to receive, integrate and responds appropriately to stimulus in the periphery, spinal cord and brain.
study about internal structure, outer structure and their functions
Navdeep Reply
circulatory system on blood pressure
Lakhu Reply
What is ELISA
(enzyme linked immunosorbent assay) is a test that uses antibodies and color change to identify a substance.
what's defense mechanism?
psychological strategies that are unconsciously used to protect a person from anxiety arising from unacceptable thoughts or feelings.
difference between apocrine sweat glands and merocrine sweat glands
Binkheir Reply
I believe the apocrine sweat gland uses a sac under the hair follicle and the merocrine sweat gland releases directly on to the surface of the skin
normal blood volume in our body
pankaj Reply
Normal blood volume in adults is 6 litres
4.7 to 5ltr.. normal for adult
what are the advantages of the concave shape of red blood cells?
Amy Reply
This structure is VERY flexible. It can allow these cells to get into the most tiny places in our bodies. a VERY good design! The advantage of red blood cells' biconcave shape is that the surface area is increased to allow more haemoglobin to be stored in the cell.
They can stack so that they can move to capillaries
what is the difference between phagocytosis and Pinosis
action of gluteus medius and minimus
Green Reply
Lateral rotation of the hip joint
Briefly explain location of ecg on a patient
Prince Reply
it is a machine that gives a graphical representation of heart beat
Briefly explain location of ecg leads on a patient?
in ecg we use electrical leads over the chest ,ancle and wrist
what is the anatomical and function difference between paravertebral and prevertebral ganglia ?
Rada Reply

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