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Activity

Herb smells and their molecules

Summary: 
Match dried and fresh herb smells. Older students can find out what chemicals make the smells.
Science content (2016 curriculum): 
Biology: Features, Adaptations of Living Things (K, 1, 3, 7)
Biology: Sensing, Organ Systems (4, 5, 6)
Chemistry: Atoms, Molecules (3-7)
Science topic (2005 curriculum connection): 
Life Science: Characteristics of Living Things (grade K)
Life Science: Needs of Living Things (grade 1)
Life Science: Plant Growth and Changes (grade 3)
Physical Science: Chemistry (grade 7)
Lessons activity is in: 
Materials: 
  • Pairs of herb smells to compare from these: herb plants (growing in a garden/cut fresh herbs); bottles/bags of the same herbs dried with contents concealed; herb essence in a bottle
  • Molecule models of herb smells e.g. carvone (mint smell), carvacrol (marjoram smell) to compare
Procedure: 

Try to match each fresh with dried herb/dried herb with herb essence/fresh herb with herb essence.

Herbs may smell strong to discourage animals from eating them.

You can smell the herbs and spices because some of the molecules leaving the herb or spice go up your nose and interact with molecules in your nose. We smell them when their unique shapes fit like jigsaw pieces into the inside of our nose, and stimulate a nerve signal to our brain, which we perceive as smell.

The pairs of fresh herbs/dried herbs/essences probably didn't have exactly the same smells as they all release slightly different mixtures of smell molecules.
However there is often a main molecule responsible for each distinctive herb smell, so we cue into this odour molecule to match the smells. Oregano has carvacrol in its smell. Anise seeds have anethole in their smell. Cloves have eugenol in their smell. Mint has L-carvone in its smell. Garlic has allyl- disulphide in its smell. Rosemary has eucalyptol in its smell.

Optional: show molecule models of the predominant molecules in mint and marjoram smells:
See if students can spot the difference between the molecules responsible for mint and marjoram smells.
Although the chemical shapes are similar, they smell very different.

Most smells are complex mixtures of many molecules so smells often mean something quite different to each of us.

Notes: 

See the "smelly booklet" from the New York Hall of Science (attached) for comparing the smells of herbs and the single molecule responsible for their smell. Single molecules difficult to obtain and store, so only done in this museum setting.

Grades tested: 
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Teacher: 
Christy Wong
Ingrid
Kecia Boecking
Teaching site: 
McBride Elementary
New York Hall of Science
Van Dusen Botanical Garden
Activity originally developed and delivered: 

Van Dusen Botanical Garden Plant Colours and Smells family activities