Something Smelly in STEM

Objective:

Learn about the sense of smell and how it affects our other senses

Background on Olfaction:

Olfaction, is the proper name for sense of smell. Our sense of smell helps us to detect hazards, such as dangerous chemicals in the air, to detect pheromones, the molecules that determine attraction between creatures of the same species, and to detect food or water, in order to help species find foods that have the nutrients they need to grow and thrive. 

The sense of smell is very important for the flavors that you perceive when you eat. The combination of the sense of taste, which senses sweet, salty, sour, bitter and umami, the sense of smell, which senses the odor of the food, flower, drink, etc… creates what we call the flavor of food. When you are sick your sense of taste can still detect sweet, salty, sour, bitter and umami but with a clogged nose it is very hard to detect the full flavor of a food, thus being sick you may notice that things taste differently.

Now that we have a bit of an idea what Olfaction is let’s learn a bit about how it works. Olfaction uses several different things:

1. Nostrils – the two openings of the nose that pull air containing odorants (the molecules of scent that bind to cells in the nasal cavity) up into the nose
2. Nasal Cavity – the large opening that contains hairs and a mucus membrane designed to trap particulates like dust and pollen, essentially acting as a filter for the body. The nasal cavity also warms and moisturizes the air before it enters the lungs.
3. Olfactory Bulb – is the sensory organ attached to the limbic system of the brain that binds to odorants and produces our sense of smell
4. Skull Bone – lies between the olfactory bulb of the brain and the nasal cavity
5. Nasal Epithelium – the tissue that lines the nasal cavity
6. Olfactory Receptors – These receptors travel from the olfactory bulb through the skill bone and through the nasal epithelium sending out tendril like ends that allow for binding of odorants, when these tendrils bind to a specific odorant a signal (Glomeruli aggregate signals) is sent to the olfactory bulb and into the limbic system, telling the brain what smell has been detected
7. Glomerulus - a spherical structure located in the olfactory bulb of the brain where synapses form between the terminals of the olfactory nerve and several other types of cells (dendrites of mitral, periglomerular and tufted cells)
8. Olfactory Receptor Neuron - is a signaling cell

Now that we know a bit about how our sense of smell works, let’s put it to the test in the following lab.

Materials

·        Section One

o   Blind folds

o   8 scent samples

o   Lab note books

o   pens

·        Section two

o   Lab glasses

o   Plastic knives

o   Scent and taste samples

·        Section three

o   Oranges

o   Wax scent cubes

Method

This lab will be a multi-section lab that allows the students to look at different aspects of smell and how each part is important to our perceptions.

Prepare Experiment

• Section One: The nose knows

a.      Have students break up into groups of two (three is ok but will make the experiment take longer)

b.      Have students create a grid in their note book that looks something like this:

Sample number	Blind folded smell	Sight and smell	Actually
Ex. 1	Orange Juice	Cotton ball and orange	Orange extract on a cotton ball

c.      Have one student dawn the blind fold. After they can no longer see have the other student waft (gently pass the open container from side to side) a random sample under the blind folded students nose.

d.      Have the blindfolded student guess what they are smelling and have the other student record their answer in the blind folded students notebook

e.      Have the students continue until the blindfolded student has smelled and guessed all of the samples.

f.       After the first student is done have the students switch roles

g.      Once the two students have completed the activity give them the answer to what each smell was a discuss why smells might be different.

• Station Two: Taste verses Smell

a.      Get together an assortment of different fruits, vegetables, etc… that the kids would not normally know:

                                                    i.     Bac Ha

                                                   ii.     Durian

                                                  iii.     Coconut

                                                  iv.     Ginger

b.      Have the students take one of the samples out and dissect it:

                                                    i.     Separate the skin from the inside

                                                   ii.     Separate the seeds (if there are any)

c.      Now smell each portion of the sample individually

                                                    i.     Does each portion smell the same or do they smell different?

d.      Now taste the fruit of the sample

                                                    i.     Does it taste like it smells?

• Station Three: Difference in Smell

a.      Have students take out the orange and wax scent samples

b.      Have the students dissect their orange

                                                    i.     Pull the skin off

                                                   ii.     Pull some of the white off

                                                  iii.     Open up a few segments

c.      Smell each part of the orange separately

d.      Rub a little bit of each part on your fingers and see if the scent rubs off

                                                    i.     Wipe your fingers in between and see if the scent still stays on those fingers

e.      Now pull out the scent block

f.       Rub the scent block on your fingers

                                                    i.     Wipe your fingers and notice that the orange peel and the scent block both leave a residual smell, try to figure out what they might have in common

Run Experiment

1. Break the kids up into 8 groups and send one group to each table
2. For each station the kids will have 5-10 minutes to work on their lab
3. Have the kids work through each section
4. After the kids have worked through each station discuss what they should have learned from each one

Analyze Data

• Section One: The smells are:

a.      Strawberry – fresh, ripe strawberries

b.      Orange Extract on cotton ball – the orange extract may smell like lime or lemon, most of the smell from an orange comes from the oil in the skin of citrus fruits, the citrus fruits have many odorants that create similar smells

c.      Banana – fresh, ripe banana

d.      Mandarin Oranges

e.      Maple Extract on cotton ball – should smell very similar but if you do not know the smell of maple syrup you would just smell a woody sweet smell

f.       Strawberry Extract on cotton ball – strawberry extract will smell different from fresh strawberries because it contains other fruit juices in order to maintain a strawberry flavor through the cooking process

g.      Maple Syrup

h.      Banana Extract on cotton ball – should smell very similar to the fresh banana

• Section Two:

a.      Bac Ha – very little taste or smell, but high in acid

b.      Onion – very stinky smell, but sweetish taste

c.      Extra sharp white cheddar – strong aroma, strong flavor

d.      Burdock Root – Earthy smell, earthy taste

• Section Three:

a.      The students should notice that most of the orange smell is contained in the orange peel. This smell comes from the oils that are found on the skin. These oils can easily be rubbed off onto one’s hands, leaving hands and tables smelling citrusy for hours possibly days after.

Conclusions

Our sense of smell developed out of necessity to help our ancestors find food, determine if the food was safe to eat and even to help them avoid predators. In todays world we still can use our sense of smell to keep us safe (gas companies add sulfur to natural gas creating a rotten egg smell that the natural gas would not otherwise have, if you smell rotten eggs in the house get out and call the gas company!), determine if food is good to eat, and to help us identify places we want to eat (think about when you are really hungry and smell something amazing and follow it to a fantastic meal).

Make It Your Own

The different smells that we used in this lab are an extremely small sampling of the various smells in the world. Just simply checking in your backpack see how many smells you can find. One thing to think about is that many people identify that crayons and the smell that they have is one of the most pleasant smells they know of. Do you have anything like that for yourself?

Extension Activities to do at home

Your home is filled with smells, most of them safe but some of them very dangerous. Think about the cleaning products that your parents use. Some of them like Hydrogen Peroxide (typically comes in a brown bottle) have little to no smell. With hydrogen peroxide it breaks down into water over time so if you smell hydrogen peroxide it will smell mostly like water. The danger with this is that if drunk the hydrogen peroxide can make your stomach bleed and make you very sick. With your parents help/permission and observation pour a small cup of hydrogen peroxide and a small cup of water (it would be best to have your parent do this so they can keep track of the cups). Now smell each by gently wafting the liquid under your nose, make sure not to inhale the liquid or to drink it (remember safety first!). Can you figure out which one is the hydrogen peroxide?