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Smell Bottles

Are you a smell expert?

In this activity, students try to identify substances using only their sense of smell. Sometimes the sense of smell can be fooled because humans do not get as full and complete a picture from smell as we do with vision.

What are smells?

What makes up the smell of something? Smells or odours are composed of tiny molecules of chemicals invisible to the human eye from things like food, flowers or poo. Many odours are not single scents or single kinds of molecules but a whole mixture of them. Everything you smell, therefore, gives off molecules. Those molecules are generally light, volatile (easy to evaporate) chemicals that float through the air into your nose.

How do we smell?

The sense of smell, called olfaction, involves the detection and perception of chemicals floating in the air. Chemical molecules enter the nose and dissolve in mucous within a membrane called the olfactory epithelium. In humans, the olfactory epithelium is located about 7 cm up and into the nose from the nostrils. The olfactory epithelium contains special receptors that are sensitive to odor molecules that travel through the air.

When the smell receptors are stimulated, signals travel along the olfactory nerve to the olfactory bulb. There the smells are recognized because each smell molecule fits into a nerve cell like a lock and key. The olfactory bulb is underneath the front of your brain just above the nasal cavity. Signals are sent from the olfactory bulb to other parts of the brain. The brain interprets the combination of receptors to recognize any one of about 10,000 different smells. Identifying smells is your brain's way of telling you about your environment.

In humans, there are about 40 million olfactory receptors; in the German Shepherd dog, there are about 2 billion olfactory receptors. That’s why dogs have a much better sense of smell than humans.

When you have a cold and your nose is stuffed up, you cannot smell very well. This is because the molecules that carry smell cannot reach the olfactory receptors. This is also why you cannot taste food properly when you have a cold. The ability to smell and taste go together because odours from food allows us to taste more fully.

How is smell related to memories and feelings?

Olfactory receptors are directly connected to the limbic system, the most ancient and primitive part of the brain, which is thought to be the basis of emotion. And so, smelling an odour consists not only of the sensation of the odour itself but of the experiences and emotions associated with these sensations. In this way, smelling certain odours can result in strong emotional reactions and trigger forgotten memories. Smell is better at this memory cue effect than any of the other senses.

How can smell keep us safe?

Your sense of smell also can help you keep safe. For example, it can warn you not to eat something that smells rotten or help you detect smoke before you see a fire.

What can we smell?

Even though humans can distinguish approximately 10,000 diverse scents. It is thought that we have seven primary odours that help us determine objects and/or our environment:

OdourExample
CamphoricMothballs
MuskyPerfume/aftershave
FloralRoses
PeppermintMint gum
EtheralDry cleaning fluid
PungentVinegar
PutridRotten eggs

How does the ability to smell vary?

Our smelling ability increases to reach a plateau at about the age of eight, and declines in old age. Women consistently outperform men on all tests of smelling ability.

Objectives

  • Describe how the body detects and responds to different smells.

Materials

  • Per Class or Group:
    small lidded canisters, foil-wrapped test tubes or large drink containers
    nail
    marker pen
    cotton wool balls or tissue wads
    a variety of substances that release odour molecules (e.g. oil of wintergreen, almond extract, maple syrup, orange oil, lemon juice, cloves or clove extract, onions, garlic, vanilla extract, vinegar, tomato ketchup, cinnamon, coffee, perfume)
    pens
    sheets of paper

Key Questions

  • Why is it difficult to guess the substance by using just your sense of smell?
  • Why does one substance elicit several different answers?

What To Do

Set up

  1. Place a cotton wool ball in the bottom of each container.
  2. Poke a few holes in each lid using a small nail, if needed. If this is not possible, the students can unscrew the lids to smell the contents.
  3. Just before the students arrive, place a few drops of each odour to be tested in a separate container.

Teacher tip:  Mark each container with a number or symbol so that only you know the true identity of each odour.

Activity

  1. Give each student a pen and paper (plus a blindfold if necessary).
  2. Pass out the bottles and so that the students can attempt to identify what they smell.
  3. Explain that the nose allows you to make sense of what is going on in the world around you.
  • Just as your eyes give you information by seeing and your ears help you out by hearing, the nose lets you figure out what is happening by smelling. It does this with help from many parts hidden deep inside your nasal cavity and head.
  • The body organs for smelling are inside the nose. They are the two olfactory membranes under the bridge of our noses about as big as postage stamps. (The rest of the nose is used for breathing in and filtering air headed for the lungs).
  • The mucus, or snot, inside our noses is used to dissolve the odour molecules breathed in so that the membranes can detect them.
  • ​The membranes’ detection messages go straight to the part of our brain that stores feelings and memory without any detours through the cerebral cortex (the main brain). This way we immediately know if a smell is chocolate and we love it or if a smell is burning trash and dangerous.

Extensions

  • Try a scent matching activity by preparing two sniff bottles of each substance. Encourage the students to find the matching pairs.
  • Take a poll of the students' favourite smells.
  • Ask the students to rate the sniff bottles in order and compare the results on the board (or a large sheet of a paper). Vanilla is thought to be the most universally pleasing scent
  • Introduce the limbic system of the brain and its relation to our sense of smell. The part of the brain responsible for our sense of smell, the limbic system, is related to feelings and memory. Sometimes our perceptions of odours can get mixed up in memories: The aroma of turkey on Thanksgiving, the pine smell of Christmas, the woody smell of the season's first barbecue all evoke strong memories and emotions. However, this can sometimes be helpful - many people do not recognize the smell of maple until you prompt them with a word like “pancakes”.

    Plus, smelling certain things can make you feel happy because you remember somebody important or a special time you experienced. Smell is better at this memory cue effect than any of the other senses. Damage to the temporal cortical region of the brain - the site of memory - does not affect the ability to detect smell, but does prevent the identification of the odour. We must first remember a smell before identifying it.
  • Discuss with the students any memories or feelings they had when smelling the sniff bottles and explain why this happens.