Out-of-class Activities and Projects

February 2013 Teacher's Guide for
Sniffing Out Cancer
Table of Contents
About the Guide ............................................................................................................ 2
Student Questions ........................................................................................................ 3
Answers to Student Questions .................................................................................... 4
Anticipation Guide ........................................................................................................ 5
Reading Strategies ........................................................................................................ 6
Background Information ............................................................................................... 8
Connections to Chemistry Concepts ........................................................................ 15
Possible Student Misconceptions ............................................................................. 16
Anticipating Student Questions ................................................................................. 16
In-class Activities ........................................................................................................ 18
Out-of-class Activities and Projects .......................................................................... 19
References ................................................................................................................... 19
Web sites for Additional Information......................................................................... 20
About the Guide
Teacher’s Guide editors William Bleam, Donald McKinney, Ronald Tempest, and Erica K.
Jacobsen created the Teacher’s Guide article material. E-mail: bbleam@verizon.net
Susan Cooper prepared the anticipation and reading guides.
Patrice Pages, ChemMatters editor, coordinated production and prepared the Microsoft Word
and PDF versions of the Teacher’s Guide. E-mail: chemmatters@acs.org
Articles from past issues of ChemMatters can be accessed from a CD that is available from the
American Chemical Society for $30. The CD contains all ChemMatters issues from February
1983 to April 2008.
The ChemMatters CD includes an Index that covers all issues from February 1983 to April
The ChemMatters CD can be purchased by calling 1-800-227-5558.
Purchase information can be found online at www.acs.org/chemmatters
Student Questions
1. What is a Volatile Organic Compound (VOC)?
2. For people with tumors, what body products can carry or contain VOCs?
3. Volatility of an organic compound depends on its vapor pressure. What is meant by vapor
4. Describe the chemical properties of reactive oxygen species and how they are related to
5. What is the relationship between VOCs and reactive oxygen species?
6. Give two advantages when choosing dogs over chemical instrumentation for cancer
7. What types of cancer are dogs capable of detecting?
8. What two biological products of the body are sniffed by dogs in detecting cancer?
Answers to Student Questions
1. What is a Volatile Organic Compound (VOC)?
A volatile organic compound is a molecule that evaporates or sublimates from a liquid or
solid phase of the same substance.
2. For people with tumors, what body products can carry or contain VOCs?
Some of the body products containing VOCs include exhaled breath, urine, and stool,
among others.
3. Volatility of an organic compound depends on its vapor pressure. What is meant by
vapor pressure?
“Vapor pressure is the pressure at which vaporized molecules reach equilibrium with the
solid or liquid phase of the same substance in a closed system.”
4. Describe the chemical properties of reactive oxygen species and how they are related
to cancer.
Reactive oxygen species are molecules with unpaired valence electrons that make them
highly reactive with surrounding biological materials. If reactive oxygen species are in
excess, perhaps because of a deficiency of antioxidant molecules that keep reactive oxygen
species in check, then they can damage DNA and healthy cell tissue. This damaging
process is known as oxidative stress and is known to be a precursor of cancer.
5. What is the relationship between VOCs and reactive oxygen species?
Under oxidative stress as outlined in answer #4, “reactive oxygen species oxidize fats in cell
membranes, resulting in increased emissions of VOCs ..”. Dozens of specific VOCs have
been linked to various types of cancer. Tumors produce changes in not just one type of
VOC, but many.
6. Give two advantages when choosing dogs over chemical instrumentation for cancer
A dog’s nose is a highly efficient chemical sensor, ready-made to sniff cancer VOCs.
Second, a dog can detect a cancer through smelling VOCs without needing to know the
specific chemical or chemicals present in the vapor. A chemical instrument can only be
designed when a specific chemical to be detected is known.
7. What types of cancer are dogs capable of detecting?
Dogs that are trained can detect skin, breast, lung, prostate, colon, bladder, and ovarian
8. What two biological products of the body are sniffed by dogs in detecting cancer?
The two biological products sniffed for cancer-produced VOCs are urine and exhaled air.
Anticipation Guide
Anticipation guides help engage students by activating prior knowledge and stimulating student
interest before reading. If class time permits, discuss students’ responses to each statement
before reading each article. As they read, students should look for evidence supporting or
refuting their initial responses.
Directions: Before reading, in the first column, write “A” or “D” indicating your agreement or
disagreement with each statement. As you read, compare your opinions with information from
the article. In the space under each statement, cite information from the article that supports or
refutes your original ideas.
1. A report of a dog alerting his owner to a malignant melanoma was first
published in 2002.
2. Vapor pressure depends on intermolecular forces.
3. Cancerous cells produce different concentrations of volatile organic
compounds (VOCs) than healthy cells do.
4. A dog’s sense of smell is up to 100,000 times better than a human’s sense of
5. Cigarette smoke interferes with a dog’s ability to detect lung cancer in a
patient’s breath.
6. Researchers need to know what chemical they are looking for before they can
train dogs to detect cancer-related smells.
7. Artificial noses are being developed that will eventually take over the work of
dogs in detecting cancer in human patients.
8. All VOCs in our environment are harmful to human beings.
Reading Strategies
These matrices and organizers are provided to help students locate and analyze information from
the articles. Student understanding will be enhanced when they explore and evaluate the
information themselves, with input from the teacher if students are struggling. Encourage
students to use their own words and avoid copying entire sentences from the articles. The use of
bullets helps them do this. If you use these reading strategies to evaluate student performance,
you may want to develop a grading rubric such as the one below.
Complete; details provided; demonstrates deep
Complete; few details provided; demonstrates
some understanding.
Incomplete; few details provided; some
misconceptions evident.
Very incomplete; no details provided; many
misconceptions evident.
So incomplete that no judgment can be made
about student understanding
Teaching Strategies:
1. Links to Common Core State Standards: There are several opportunities to compare
alternatives in this issue of ChemMatters. For example, you might ask students to take
sides and find support for one of the following:
a. Using brand-name vs. generic drugs
b. Driving electric cars vs. cars with internal combustion engines
2. To help students engage with the text, ask students what questions they still have about
the articles.
3. Vocabulary that may be new to students:
a. VOCs
b. Internal combustion engine
4. Important chemistry concepts that will be reinforced in this issue:
a. Reaction rate
b. Oxidation and reduction
Directions: As you read, describe they VOCs produced in cancer cells, then compare how dogs
and machines can detect cancer in humans.
What are they?
How are VOCs produced by cancer
cells different from those produced by
normal cells?
Artificial Noses
Future use in
Background Information
(teacher information)
More on Volatile Organic Compounds
Volatile organic compounds (VOCs) are found in a wide range of compounds that are
found in everyday products: paints, adhesives, fuels, sol-vents, coatings, permanent marker
pens, polish remover, dry cleaning agents, feedstocks, refrigerants, aerosol sprays, and moth
repellents among others. Some of the worst VOCs in terms of health problems include benzene,
methylene chloride and perchloroethylene. When you experience a strong chemical smell you
are most likely smelling a VOC. Some manufacturers of VOC-containing products label them as
“low VOC” or “VOC free”. There is no international standard for defining VOCs.
VOC exposure can cause asthma and allergies. Exposure to certain VOCs has been
shown to cause cancer in test animals and is widely suspected to do the same for people.
Benzene, the VOC found in cigarette smoke is definitely carcinogenic. Another VOC that can
cause allergies in children and respiratory problems in adults is formaldehyde. This VOC is
found in adhesives, furniture varnishes and plywood. Alternatives to formaldehyde-containing
glues and adhesives include soy-based adhesives. The chemical behavior of this glue is similar
to the abyssal threads used by mussels to cling to rocks!
From one study, it is difficult to determine to what degree VOCs are responsible for
causing cancer. The study estimates that only about 2% of cases are due to air borne volatile
organic chemicals. Tracking the precise exposure of a large number of individuals to specific air
toxicants in the different and unique environments to which they subject themselves presents a
formidable task.
More on the sense of smell
Our sense of smell comes about because of specialized nerves in our nose in a
specialized area known as the olfactory bulb. Supposedly we are able to distinguish over
10,000 different odor molecules. Inhaled air through the nose passes over a bony plate
that contains millions of olfactory receptor neurons in an epithelial cover. These olfactory
nerves have cilia extending out into a mucosal lining that is exposed to the atmosphere.
The cilia contain olfactory receptors which are specialized proteins that bind low
molecular weight molecules (odorants). Each receptor has a pocket (binding site) that
has a particular shape that will match either a specific molecule or a group of structurally
similar molecules.
Research done by Linda Buck and Richard Axel (joint recipients of the 2004
Nobel Prize in Physiology) suggests some 1,000 genes that encode the olfactory
receptors for a particular type of odorant molecule. The interaction of the right molecule
with the right receptor causes the receptor to change its shape (called its structural
conformation). The conformational change generates an electrical signal that goes to the
olfactory bulb and then to the areas of the brain where any one nerve impulse is
“interpreted” as a particular smell. Within the olfactory bulb it is thought that groups of
olfactory receptors produce spatial patterns of olfactory bulb activity that are
characteristic for a given odorant molecule or a blend of odorant molecules. These spatial
patterns of activity create the information that leads to the recognition of odor quality and
intensity between odors. The information is processed at higher levels of the olfactory
system and in the brain to produce the perception of smell.
Buck and Axel studied a type of cell found in the nose called olfactory receptor
cells, and a family of proteins called receptor proteins found in those cells. By studying
mouse olfactory receptor cells, they found that each such cell contained only one type of
receptor protein. In mice there are over 1,000 different kinds of receptor proteins,
although humans may possess only about 350. … A relatively large part of the genome
of any given mammal is devoted to coding for receptor proteins. With so many different
kinds of receptor proteins, as much as 3% of a mammal’s gene codes for the proteins
involved in odor reception.
Proteins are long chain-like molecules, made by joining together many amino
acid molecules. Receptor proteins are found at the surfaces of receptor cells, and the
proteins snake in and out of the cell membrane, crossing it seven times. In the process,
receptor proteins are twisted and bent into different shapes, creating cavities of different
shapes and sizes. Each receptor protein has a different cavity shape. Odorant molecules
can dock with these cavities in the receptor proteins. The shape of the cavity of a
particular receptor protein is shaped to allow only members of specific families of
molecules to dock with it, in the familiar lock-and-key manner of protein-substrate
chemistry. This means that each kind of receptor protein responds to only a specific
family of compounds. While a human may only have 350 or so different kinds of receptor
cells, many odors are made of combinations of substances. Humans can discern as
many as 10,000 different odors, that is, 10,000 different combinations of substances. In
addition, within a chemical family, different members may not bind to the same receptor
protein, allowing additional levels of nuance in the smell that is perceived.
(ChemMatters Teacher’s Guide (pp. 10–11), for Ebach, C. What’s That Smell?
ChemMatters 2012, 30 (4), pp 12–14,
The original paper by Buck and Axel with all the experimental details and data (including
the nucleotide sequences) can be found at
A complete description of the work by Buck and Axel from the Nobel Prize committee is
found at http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html.
More on specialized smell in dogs
When it comes to detecting odors, dogs have a very highly developed sense of
smell, in part because a larger portion of their brain is designed for neural activity from
their nasal passages. A comparison of humans with different dog breeds and their neural
capacity is shown below:
Table: Scent-Detecting Cells in People and Dog Breeds
of Scent
Fox Terrier
German Shepherd
(Teacher’s Guide for Ebach, C. What’s That Smell? ChemMatters 2012,
30 (4), pp 12–14,
Inside the nose, receptor cells are attached to a tissue called the olfactory
epithelium. In humans, the olfactory epithelium is rather small, and only covers a small
part of the surface of the inside of the nasal cavity near the cavity’s roof. In dogs,
however, the olfactory epithelium covers nearly the entire surface of the interior of the
nasal cavity. On top of this, a long-snouted tracking dog like a bloodhound or a basset
hound may have a considerably larger nasal cavity than a human. All in all, the olfactory
epithelium of a dog may have up to fifty times the surface area as that of a human. While
a human may have around 3 cm 2 of olfactory epithelium, a dog might have up to 150
A dog’s wet nose also helps it smell more acutely, as odorants are captured as
they dissolve in the moisture. The shape of the interior of a dog’s nasal cavity also allows
odors to be trapped inside during inhalation, without being expelled during exhalation.
This allows odorants to concentrate inside the dog’s nose for easier detection. When
dogs exhale, the spent air exits through the slits in the sides of their noses. The manner
in which exhaled air swirls out actually helps usher new odors into the dog’s nose. This
also allows the dog to sniff more or less continuously. And they smell stereophonically,
that is, they can determine the direction of the odorant molecules depending on which
nostril detects the odor. A dramatic result of all of these adaptations is that dogs can
smell certain substances at concentration up to 100 million (1 x 108) times lower than
humans can.
(Sniffing Landmines. ChemMatters 2008. 28 (2),
rchive/WPCP_008628; Teacher’s Guide access at
A 3-D model of a dog’s nasal passage and neural connections:
The canine nasal airway: (a) Three-dimensional model of the left canine nasal airway,
reconstructed from high-resolution MRI scans. (b) The olfactory recess is located in the rear of the
nasal cavity and contains scroll-like ethmoturbinates, which are lined with olfactory epithelium.
The olfactory (yellowish-brown) and respiratory (pink) regions shown here correspond to the
approximate locations of sensory (olfactory) and non-sensory (squamous, transitional and
respiratory) epithelium, respectively (Craven et al. 2007).
(Teacher’s Guide (pp 12–15), for Ebach, C. What’s That Smell? ChemMatters)
Beagles, bloodhounds, and basset hounds have been bred to have especially
keen senses of smell, even for dogs. They can be trained to discriminate between
various chemical odors, sniffing out land mines, bombs in luggage, drugs at border
crossings—and now they are being used in medical diagnosis (cancer in particular).
Dogs are trained to detect odors, too faint for humans to smell, that indicate a diabetic
patient might be about to go into insulin shock, a condition that results when blood sugar
levels drop dangerously low, and can lead to coma and even death. When the dog smells
insulin shock on the way, it can alert the patient to take preventive measures, like eating
something sweet. If the insulin shock comes while the patient is asleep, a barking dog
can be a lifesaver.
(Sniffing Landmines. ChemMatters 2008, 28 (2), Teacher’s Guide; access at
In the future, dogs may also be used to smell cancers while still too small to be
detected by conventional means. Some studies that have been done with what are called
sniffer dogs are able to detect some of the chemicals being exhaled by patients with lung
cancer. In some well controlled experiments, dogs were able to detect lung cancer from
exhaled breath in 71 of 100 test cases and determined that 372 of 400 other patients did
not have lung cancer. In addition, the dogs could discern lung cancer from other lung
problems such as chronic obstructive pulmonary disease, even sniffing accurately
through the exhaled breath of patients that just smoked a cigarette. The dogs are
detecting volatile organic compounds being emitted from cancerous cells in the very early
stages, which other medical tests or diagnostic technologies are not able to do. Other
studies have shown that urine of cancer patients contain volatiles that are detectable by
dogs. The ideal would be to identify the particular marker molecules after which an
electronic detector might be developed.
(ChemMatters Teacher’s Guide (p 14), for Ebach, C. What’s That Smell? ChemMatters)
More on pheromones
Chemical senses are the oldest of senses, shared by all organisms including
bacteria. Very recently, it has been determined that several species of bacteria can
detect very specific chemicals. Several species of soil bacteria have their own “noses” for
detecting airborne ammonia, an important nitrogen source for the bacteria’s protein
metabolism. Most animal olfactory systems have a large range of relatively non-specific
olfactory receptors, which means that almost any chemical in the rich chemical world of
animals will stimulate some olfactory sensory neurons and can potentially evolve into a
pheromone. A pheromone is a molecule used for communication between animals of the
same species. [The word pheromone comes from the Greek, pherein, to carry or
transfer and hormon, to excite or stimulate.] Across the animal kingdom, more
interactions are mediated by pheromones than by any other kind of signal. There is a
certain commonality between vertebrates and invertebrates in terms of the pheromones
produced and in the range of behaviors that pheromones influence.
Insects such as ants use pheromones to direct their “colleagues” to a food
source and find their way back to the colony. They also have other pheromones to
 mark the way to new nest sites during emigration
 aggregate
 mark territories
 recognize nest mates.
Mating activities of moths depend upon the male detecting the odors emitted by
the female of the species. Chemical knowledge of this “mating” pheromone or sex
attractant has been used to lure male moths into traps to limit reproduction of moths that
are destructive to plants, such as the Gypsy moth. But other animals as large as the
elephant make use of pheromones, primarily for reproductive purposes (sexual
signaling). An interesting note is the fact that the pheromone used by elephants is the
same molecule used by 140 species of moth! Yet there is no interaction between the two
groups of animals because the receptors and the signals produced are different! Dogs
like many other mammals (except humans) respond to pheromones meant to indicate
mating readiness and other sexual details. Since we were talking previously about the
highly sensitive olfactory system in the dog, it turns out that the dog possesses a special
olfactory structure in its nose for detecting pheromones in the mix of chemicals that come
through its nasal channels. This structure is called Jacobson’s organ; it is located in the
bottom of the dog’s nasal passage. ”The pheromone molecules that the organ detects—
and their analysis by the brain—do not get mixed up with odor molecules or their
analysis, because the organ has its own nerves leading to a part of the brain devoted
entirely to interpreting its signals. It's as if Jacobson's organ had its own dedicated
computer server. (http://www.pbs.org/wgbh/nova/nature/dogs-sense-of-smell.html)
Some known pheromone molecular structures are shown here.
Chemical composition of certain pheromones: (1) sex attractant of female of
Asiatic silkworm, (2) marking substance of certain bumblebees, (3) aphrodisiac of male
of Danaidae butterfly, (4) attractant of female of gypsy moth, (5) component of marking
secretion of a rodent (clawed jird), (6a, 6b, 6c) three components of clustering
pheromone of Scolytus bark beetle, (7) anxiety pheromone of Lasius ant
There are defined criteria for a pheromone. “The general size of pheromone
molecules is limited to about 5 to 20 carbons and a molecular weight between 80 and
300. This is because below 5 carbons and a molecular weight of 80, very few kinds of
molecules can be manufactured and stored by glandular tissue. Above 5 carbons and a
molecular weight of 80, the molecular diversity increases rapidly and so does the
olfactory efficiency. Once you get above 20 carbons and a molecular weight of 300, the
diversity becomes so great and the molecules are so big that they no longer are
advantageous. They are also more expensive to make and transport and are less
volatile. In general, most sex pheromones are larger than other pheromones. In insects,
they have a molecular weight between 200 and 300 and most alarm substances are
between 100 and 200.” (Sociobiology: The Abridged Edition, 1980, 114)
Besides the category of pheromone associated with sexual signaling, there are
alarm pheromones that are released to promote fight and flight reactions in receivers.
Many ant species release the same pheromones to repel an opponent and an alarm to
recruit fellow ants for assistance in a battle with the invaders. In other animals, alarm
pheromones are used to make flesh unpalatable or toxic to a predator. These substances
would be released by an injured animal. There are a variety of sea organisms that use
this technique.
(ChemMatters Teacher’s Guide (pp 15–16), for Ebach, C. What’s That Smell?
More on specialized smell in fish
The function of smell in non-humans is more than just imbibing on pleasant (or unpleasant)
Being able to smell particular chemicals serves a most interesting purpose for
salmon—their ability to return to their place of birth several years later to repeat the
reproductive cycle. Classic experiments done by Arthur D. Hasler in the 1950s clearly
demonstrated that salmon can smell particular chemicals in a stream that are associated
with the migration route that the salmon takes after hatching to return to the ocean. If
their nostrils are blocked, the salmon are unable to follow a particular stream of water that
contains the chemical clues. The memory of those smells serves the salmon several
years later when they begin the migration from the sea back to the fresh water stream, a
distance of 800 to 900 miles away where they developed in and hatched from eggs. It is
not known just exactly how the mature salmon find their way along the coastline (Pacific
and Atlantic) to zero in on a particular fresh water river that empties into the ocean. There
are ideas that for the ocean portion of the return trip, salmon use some navigational tools
in the open water that include day length, the sun’s position and the polarization of the
light that results from the angle in the sky, the earth’s magnetic field, water salinity and
temperature gradients. Whatever the combination of tools, the salmon are able to find
where their natal waters discharge into the ocean.
Young salmon (smolts) are particularly sensitive to the unique chemical odors of
their locale when they begin their downstream migration to the sea. Odors that the smolts
experience during this time of heightened sensitivity are stored in the brain and become
important direction-finding cues years later, when adults attempt to return to their home
streams. In one early experiment, salmon that were reared in one stream and then
moved to a hatchery during the smolt stage returned to the hatchery, demonstrating the
crucial role of imprinting during the transformative period of the fish’s life. Recent work
has suggested young salmon may go through several periods of imprinting, including
during hatching and while emerging from their gravel nest. (A good reference on studying
olfaction in salmon in detail is found at
(ChemMatters Teacher’s Guide (p 12), for Ebach, C. What’s That Smell? ChemMatters)
More on olfactory fatigue
One of the interesting neural responses of our olfactory system is a
disappearance of the recognition or registration of a particular smell in the air being
inhaled, over a short period of time. The neural receptors for smell eventually stop
sending signals to our brain for interpretation of a particular smell. This is known as
olfactory fatigue.
Have you ever noticed a particular scent upon entering a room, and then not
noticed it ten minutes later? This is due to olfactory fatigue. The olfactory sense is unique
because it relies on mass, not energy to trigger action potentials. Your ears do not "stop"
hearing a sound after a certain period of time, nor do your eyes stop seeing something
you may be staring at. This is because both the ears and the eyes rely on energy to
trigger them, not mass. In the nose, once a molecule has triggered a response, it must be
disposed of and this takes time. If a molecule comes along too quickly, there is no place
for it on the olfactory hairs, so it cannot be perceived. To avoid olfactory fatigue, rabbits
have flaps of skin that open and close within the nostrils. This allows for short, quick
sniffs and lets the rabbit "keep in close odor contact with its environment." When we wish
to fully perceive a scent, we humans also smell in quick, short sniffs, often moving the
source of the smell in front of one nostril then the other. This behavior also prevents odor
fatigue. (Stoddard & Whitfield, 1984)
An interesting trick or technique to counter olfactory fatigue in perfume shoppers
is to have containers of coffee beans on the store counter which tend to
‘reset’ olfaction. Anosmia is the permanent loss of the sense of smell, and is different
from olfactory fatigue. (Wikipedia, http://en.wikipedia.org/wiki/Olfactory_fatigue)
(ChemMatters Teacher’s Guide (pp16–17), for Ebach, C. What’s That Smell?)
Connections to Chemistry Concepts
(for correlation to course curriculum)
1. Organic compound—Any chemical that contains carbon (except carbon monoxide, carbon
dioxide and metal carbonates) is considered an organic compound. Because of the bonding
based on the carbon atom, organic compounds have an almost infinite number of
configurations with important “functional” groups attached. The size of the molecules of
organic compounds is wide-ranging. It is thought that a truck tire of synthetic or natural
rubber, an organic polymer, is a single molecule!
2. Kinetic molecular theory of gases—Because gas molecules are constantly in motion,
volatile substances can reach our nose from a source at some distance from us.
3. Phase change—Although a volatile organic compound can exist in a biological solution, it
can only be detected by a dog’s nose if the compound undergoes a phase change from
liquid to a gas (evaporation). But to be detected in the nose, the gas has to then go into
4. Reactive Oxygen Species (ROS)—These molecules that are considered chemical radicals
(meaning they have unpaired electrons within a molecule) are considered to be highly
reactive and can cause damage to cells and tissues, including DNA structures. This in turn
can potentially alter the behavior of a functioning cell because of changes in the formation of
specific enzymes that are under DNA control. Alteration of enzymes affects biochemical
5. Antioxidant—This category of chemical, found within cells as well as in the intercellular
fluid, can latch on to reactive oxygen species and prevent them from damaging important
biological molecules such as enzymes and other proteins. There are both water-soluble as
well as lipid soluble types. Vitamin E and C are considered to be the most abundant and
effective of the antioxidants.
6. Volatile Organic Compounds (VOC) —There are many volatile organic compounds that
are not necessarily connected to biological situations, including the cancer state. Commonly
occurring VOCs include formaldehyde, benzene, methylene chloride, perchloroethylene,
methyl tert-butyl ether (MBTE), methane (often separately classified), chlorofluorocarbons,
styrene and limonene. These compounds have to have high vapor pressure which in turn
suggests they have weaker intermolecular bonds than non-volatile compounds. The lack of
strong intermolecular bonds is determined by the molecular structure itself.
7. Polar, nonpolar—Volatility of compounds (the ease which liquids vaporize) is dependent on
the types of intermolecular bonds that exist. These bonds in turn depend on intramolecular
bonds, some of which can produce polar or nonpolar molecules. Nonpolar molecules will
have lower boiling points and higher vapor pressures compared with polar molecules of
similar molecular weight.
Possible Student Misconceptions
(to aid teacher in addressing misconceptions)
1. “Taking anti-oxidants, such as vitamins, will prevent developing cancer.” Although
some investigators suggest a link between excessive reactive oxygen species and damage
to DNA which in turn might cause cancer, there is no definitive connection. In fact, it is
known that DNA can repair itself. Taking anti-oxidants such a vitamin E or C could reduce
the number of reactive oxygen species. It does not mean we have eliminated a known
cause of cancer, however.
2. “We have a limited number of odors that we can detect.” OK, this isn’t really a
misconception, but it comes close; it seems as if our olfactory system can detect up to
10,000 different odorants, which seems to be quite extensive!
3. “Liquids evaporate or vaporize only at high temperatures, as in the boiling of water.”
The temperature at which a liquid evaporates, whether at the boiling point or not, is
dependent on the molecular structure of the molecule which in turn determines the type of
intermolecular bond. If you compare the rate at which water evaporates at room temperature
and an organic compound such as carbon tetrachloride (CCl4), you find that carbon
tetrachloride will evaporate much quicker than water because the intermolecular bonds
between the carbon tetrachloride molecules are much weaker than those between water
molecules. The type of intermolecular bond results from the bonding within the molecules.
The water molecule ends up being a polar molecule which means it possesses slight
electrical charges of plus and minus on opposite ends of the structure (dipoles). This allows
for attractive forces between water molecules (plus to minus). The carbon tetrachloride
molecules are the exact opposite or non-polar. The intermolecular bonds are much weaker
than that of water. So it takes less kinetic energy for separation of carbon tetrachloride
molecules in the evaporative process. The molecules do not have to reach the boiling point
in order to evaporate because some of the molecules have enough kinetic energy to break
intermolecular bonds and become gaseous. Non-polar molecules create a higher vapor
pressure (from more gaseous molecules) at a given temperature than polar molecules
because of their weaker intermolecular bonds. NOTE: Vapor pressure relies on the
existence of three distinct types of intermolecular forces- London forces (temporary dipoles),
present in all molecules, dipole-dipole interactions, which are the result of polarized
structure, and hydrogen bonds, which are the result of a hydrogen atom covalently bonded
to a highly electronegative atom (such as oxygen) in a polarized structure.)
Anticipating Student Questions
(answers to questions students might ask in class)
1. Is smell different than taste? Do fish ‘smell’ food or do they ‘taste’ the food?”
Depending on the type of animal, there can be separate locations for taste detection
(e.g., taste buds or receptors) and smell detection (e.g., olfactory receptors). In the
case of fish, there are olfactory receptors in their nasal passages for the detection of
various types of molecules in the water including those that identify the type of water
(related to homing instincts in salmon) or the presence of another fish of the same
species. So fish smell food. But they are also able to taste with taste buds on their
lips and on the roof of their mouths as well as on the gills. They do not have taste
buds on their tongue as is true for humans. For humans, we taste as well as smell
food with olfactory receptors in the nose and taste buds on the tongue as well as in
the back of the throat. The taste buds detect certain “tastes”—salt, sweet, bitter, sour
and umami (“deliciousness”). Smell comes in multiple categories creating a complex
of “odors”. Sometimes smell and taste work in conjunction with each other to produce
a particular “taste”. If your taste buds are blocked, as in a cold, some flavors of food
are not detected. Chocolate’s flavor depends on smell as much as taste. If you block
out smell, the only components of the chocolate flavor will be sweetness and
bitterness (from the taste buds).
2. Why does the initial odor of a substance such as a deodorant disappear even
though the person is still in the room?” The molecules responsible for the odor of
the deodorant are still in the air and reaching a person’s nose. But the person’s
nervous system has reached what is known as olfactory fatigue. If the person who no
longer smells the odor were to leave the area of the perfume, then return, that person
would again smell the perfume for another period of time before sensory fatigue sets
3. How do the molecules of an odor become a sensation of smell?” When the
molecules associated with an odor reach the nerve endings of the olfactory sensors
in the nose, they must first go into solution (the mucosa).
This solution bathes cilia that are part of nerve endings (olfactory nerve endings)
which are an extension of what is known as the olfactory bulb. Within the olfactory
bulb are nerve endings that connect to the cilia-olfactory nerve endings, carrying a
nerve impulse to the brain. The stimulation of the nerve endings is accomplished
through specialized proteins in the cilia that bind low molecular weight molecules
(odorants). The binding of the odorant molecules to the specialized proteins causes a
change in the structure of the specialized proteins which in turn sets off an electrical
signal that passes into the olfactory bulb and on to the brain for interpretation as a
particular smell.
4. “Why are dogs more sensitive to smell than humans?” If you look at the sensory
area for smell in a dog’s brain, it is apparent that it is much more extensive than in
our brains. It is estimated that a dog has some 20 to 40 times as many receptors as
humans. If you test a dog’s ability to smell the particularly odoriferous molecule
hydrogen sulfide, it is found that the lowest concentration of hydrogen sulfide in air
that is detected is 10-13 % (0.00000000000001%, or 1000 ppt). The lowest
concentration of hydrogen sulfide detected by humans is 10-6 % (0.0000001% or 100
ppm). Note that the MSDS for hydrogen sulfide lists the short term exposure limit (10
minutes) at 15 ppm, which means we can’t even detect it at its toxic level—but dogs
(Above questions originally printed in the Teacher’s Guide (pp 18–19) for Ebach, C.
What’s That Smell? ChemMatters 2012, 30 (4), pp 12–14)
In-class Activities
(lesson ideas, including labs & demonstrations)
1. Several class lab exercises on olfactory fatigue can be found at the following Web sites:
a. http://www.sciencebuddies.org/science-fairprojects/project_ideas/HumBio_p031.shtml#materials
b. http://academic.evergreen.edu/curricular/perception/Lab1006.htm. This latter Web site
has very good questions for the students to think about with regard to the topic of
olfactory fatigue.
c. Another Web site on olfactory fatigue activity is found at
http://faculty.washington.edu/chudler/chems.html.). The teacher’s guide for this activity is
found at http://faculty.washington.edu/chudler/pdf/chemstg.pdf.
2. Another student lab exercise involves the synthesis of esters, which are normally used as
flavoring in foods, but for this exercise would simply be the production of pleasantly smelling
compounds that they can recognize. Ester synthesis involves the use of concentrated
sulfuric acid. But if done in small quantities it presents less of a lab safety issue. Or the
teacher can add the acid for the students at the correct step in the procedure. Refer to the
following Web site for a complete lab exercise in ester synthesis:
3. Although this ChemMatters article deals with smell, students could map their tongue for the
locations of the principle tastes of salt, bitter, sweet and sour (acidic). A printable outline of
the tongue with the locations on the tongue for the different categories of taste is found at
http://www.teachervision.fen.com/tv/printables/orange/SL-27.pdf. A Web site for the lab
procedure can be found at http://faculty.washington.edu/chudler/chtaste.html. You can also
actually see the taste buds on the tongue and compare the number for different people. See
the following Web site for the simple instructions:
Additional background information and discussion about the integral role of smell with taste
and touch for the sensations of what some people would call the flavor of foods is found at
http://www.tastescience.com/default.html. Smell is often involved with a particular taste. This
exercise would also point out to students the specificity of neural receptors. Most biology lab
manuals contain the exercise procedure.
4. Instructions for doing vapor pressure lab exercises follow:
a. one based on Vernier’s “LabQuest 10: Vapor Pressure of Liquids Lab” is found at
55534169,d.dmQ. The reference for the Vernier Lab Quest experiment with a list of
Vernier equipment needed is found at
http://www.vernier.com/experiments/cwv/10/vapor_pressure_of_liquids/ The most recent
listing of Vernier publications that include the chemistry experiments can be found at
http://www.vernier.com/products/books/cwv/. Finally, the basics of using Vernier Lab
Quest programs are found at
b. A second experimental procedure for measuring vapor pressure is found at
c. Another experiment to determine vapor pressure as well as heat of vaporization for more
capable students (the technique is interesting and non-electronic) is found at
Out-of-class Activities and Projects
(student research, class projects)
1. There are many interesting biological/biochemical aspects to smell in living organisms, from
bacteria to humans. How does a chemical in the air become a nerve impulse and a detected
sensation in the brain? What chemistry is involved? What is common to different animals
and their sense of smell? What is different- what types of odor molecules are detected by
what animals?
2. Students could research the connection, if any, (what research evidence?) between
antioxidants and cancer prevention. A useful reference to start is found at
3. The issue of the effectiveness of vitamins and other supplements in terms of using
antioxidant properties to prevent cancer needs to be investigated by students. A starting
point is http://blogs.scientificamerican.com/observations/2010/04/20/antioxidants-may-notbe-worth-their-salt-in-preventing-cancer/. A related study on the effectiveness of a specific
naturally occurring compound, alpha-carotene, is found at
http://blogs.scientificamerican.com/observations/2010/12/30/alpha-carotene-from-veggieslinked-to-longer-life/ . A research team found an especially strong correlation between
higher alpha-carotene levels and lower risk of death from diabetes, upper respiratory tract
and upper digestive tract cancers, as well as lower respiratory disease.
4. There are all kinds of ideas, with various degrees of supporting evidence as to the
effectiveness of antioxidants against aging, that can be researched, starting with
5. An additional reference that students could use in their research is a government site that
presents a balanced view about antioxidants and the research evidence supporting or not
supporting the effectiveness of this special class of chemicals. Refer to
(non-Web-based information sources)
The references below can be found on the ChemMatters
25-year CD (which includes all articles published during the years 1983
through 2008). The CD is available from ACS for $30 (or a site/school
license is available for $105) at this site:
http://www.acs.org/chemmatters. (At the right of the screen,
click on the ChemMatters CD image like the one at the right.)
Selected articles and the complete set of Teacher’s Guides
for all issues from the past three years are also available free online
at this same site. (Full ChemMatters articles and Teacher’s Guides
are available on the 25-year CD for all past issues, up to 2008.)
Some of the more recent articles (2002 forward) may also be available online at the URL
listed above. Simply click on the “Past Issues” button directly below the “M” in the ChemMatters
logo at the top of the page. If the article is available online, you will find it there.
Although the title suggests this article is only about pheromones, the content is about
aromas in general. The suggestion about human pheromones is not supported by scientific
evidence to date. (Kimball, A. Human Pheromones: The Nose Knows. ChemMatters 1997, 15
(2), pp 8–10)
This article may appeal to students because it explores those bodily odors that do not
qualify as attractive perfumes. It explores the origins of the typical teenager odors! (Kimbrough,
D. How We Smell and Why We Stink. ChemMatters 2001, 19 (4), pp 8–10)
This article discusses how dogs are able to detect landmines through training to
recognize specific volatile chemicals that emanate from the buried explosive device. (Vos, S.
Sniffing Landmines. ChemMatters 2008. 28 (2), pp 7–9,
A recent ChemMatters article related to smell is Ebach, C. What’s That Smell?
ChemMatters 2012, 30 (4), pp 12–14.
Web sites for Additional Information
(Web-based information sources)
More sites on a dog’s sense of smell
“This is a Nova Web site about dogs and their use in tracking things:
http://www.pbs.org/wgbh/nova/nature/dogs-sense-of-smell.html. It includes an extensive set of
references that are Web-accessible.”
(Teacher’s Guide (p 2) for Ebach, C. What’s That Smell? ChemMatters)
A series of references on dogs about their sense of smell plus training is found at the
PBS Kids Web site for Scientific American Frontiers at http://www.pbs.org/saf/1201/index.html.
Additional uses of dogs for odor detection are described in The NY Times article found
A newspaper article that describes the work of a cancer-research station, Pine Street
Foundation, which also utilizes dogs for cancer detection (and how they are trained) is found at
http://pinestreetfoundation.org/can-dogs-detect-cancer/. A short video of a dog in action is
available at http://pinestreetfoundation.org/can-dogs-detect-cancer/.
A more extensive video on the training techniques for cancer-sniffing dogs is found at
http://www.youtube.com/watch?v=IZA9R0uSGWc .
Videos on dogs detecting bedbugs and alerting diabetic conditions for a patient are
available at http://www.youtube.com/watch?v=EJ-6gvPJUI8 (bedbugs),
http://www.youtube.com/watch?v=Y-bi2FEsK4o (diabetic) and
http://www.youtube.com/watch?v=tb4WiUTAA5M (diabetic). During the past 10 years, diabetic
alert dogs have been used successfully in the management of Type 1 diabetes.
More sites on pheromones
Current thinking on human pheromones and the role of odors in human
interaction can be found at
Another site that provides a very extensive background on pheromones and their
use by various groups of animals is found at
An example of how scientists go about studying and deciphering ant behavior
that includes using pheromones is found at
A complementary article on studying the behavior of ants, in terms of detecting
scents, is found at http://blogs.scientificamerican.com/thoughtfulanimal/2011/06/23/nosejobs_for_ants/.
A Web site that is all about ants and how they communicate (includes video and
drawings of body parts important to the communication) is found at
A college Web site about pheromones might prove useful to students who adopt
the topic of pheromones for a research project. The Web site is quite extensive and also
readable. The Web address is
ntro.html .
An extensive collection of Web sites from Scientific American dealing with
pheromones can be found at
(all from Teacher’s Guide (p 23) for Ebach, C. What’s That Smell? ChemMatters)
More sites on homing traits of salmon
One site that summarizes current thinking on the ability of salmon to return to
their freshwater site of birth is found at
Additional sites that deal with salmon homing instincts are found at
http://fish.washington.edu/research/publications/ms_phd/Havey_M_MS_Sp08.pdf. (a
PhD thesis that discusses the experimental setup for evaluating imprinting on salmon)
For a story about studying the geomagnetic abilities of salmon in homing from
ocean to freshwater see
A site that shows the role of amino acids in water that salmon use for homing can
be found here:
This site gives a very complete discussion of what is known and not know about
how salmon find their way from ocean to their site of birth in an inland freshwater stream:
(all from Teacher’s Guide (p 23) for Ebach, C. What’s That Smell? ChemMatters)
More sites on using animal sense of smell for medical purposes
This site, http://www.monell.org/news/news_releases/lung_cancer_odors, is from
one of the major research centers on smell, the Monell organization. Their news
information describes the research into detecting cancer through odors in urine using
both animals and electronic chemical sensing. In this case the subjects are mice. Of
course dogs are also known to be able to detect cancer in human patients, both from
sensing volatile organic compounds emitted in a person’s breath as well as sniffing a
patient’s urine, depending on the type of cancer.
Another Web site dealing with cancer detection by dogs is found at
(two sites above from Teacher’s Guide (p 24) for Ebach, C. What’s That Smell?
Two recent scientific papers that justify the accuracy of trained dogs in detecting lung
cancer compared with electronic devices are found at
http://erj.ersjournals.com/content/early/2011/08/05/09031936.00051711 and
More sites on electronic smelling devices
Although animals such as dogs are available, if trained, to sniff out a variety of materials
including medical odors, drugs, and explosive devices, there continues to be research into
electronic devices for detecting a whole host of vapors. The basis for some of these devices is
explained at this Web site: http://techno-glitz.blogspot.com/2008/03/electronic-smell.html.
Another electronic device for detecting cancer uses a nuclear magnetic resonance
scanner that detects specific antibodies (with injected magnetic particles) associated with
cancerous cells. The device is reported to have a 96% accuracy rate, 12% higher than other
standard methods. A “smartphone” can be programmed to read the results based on analysis of
nine protein markers associated with cancer cells. The device is quite small and portable. Refer
to this Web address:
Another electronic device developed specifically to detect heart failure conditions with an
explanation of how the device works is found at http://news.cnet.com/8301-27083_3-20098835247/could-an-electronic-nose-sniff-out-heart-failure/?part=rss&subj=news&tag=2547-1_3-0-20.
More sites on chemical-based cancer detectors
The Web site http://news.bbc.co.uk/2/hi/health/6387773.stm describes the development
of an inexpensive chemical test to detect VOCs given off from lung cancer patients. Because it
is based on color changes, expert analysis is not required. And the accuracy of the test is about
75% including detection of very early tumors which is very important in the case of lung cancer
which needs very early detection in order to have any success in treatment.
More sites on Reactive Oxygen Species (ROS) and antioxidants
Two Web sites that provide chemical information on reactive oxygen species are
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/ROS.html, which may be useful in
class because of the electronic structures of ROSs that are shown, and
http://lpi.oregonstate.edu/f-w97/reactive.html, which is an academic Web site of the Linus
Pauling Institute (LPI). This site discusses the role of ROSs in a biological/biochemical context
along with how certain vitamins, particularly Vitamin C and E, may play a role as antioxidants to
counter the effects of ROSs. Among other things, Linus Pauling discovered several important
properties of bonding that included hybridization and resonance. He also explained the
properties of ionic solids. This Web site of the LPI may prove useful for future classes as it
includes biographical details of Linus Pauling’s life work in chemistry.
An extensive Web site (fact sheets) on antioxidants and cancer is at the National Cancer
Institute and is found at http://www.cancer.gov/cancertopics/factsheet/prevention/antioxidants.
Among other things is scientific information on various research projects (clinical trials) that are
investigating connections between antioxidants, such as vitamins, and the prevention of cancer.