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Activity

Smell pairs: herbs and plants

Summary: 
Pair up fresh and dried herbs, or herbs and their essence, by smell. Optional: look at the smell molecule shapes.
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)
Lessons activity is in: 
Materials: 

Fresh herb match with dried herb (photos):

  • 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

Plant part match with smell of essence:

    Plant samples, and their odour in an opaque squeezy bottle, suggestions below:
  • coffee beans, in a glass jar, and in an opaque plastic squeezy bottle
  • lemon slices in a glass jar and lemon essence in an opaque plastic squeezy bottle
  • cedar wood piece in a glass jar and cedar essence or odiforous cedar wood in an opaque plastic squeezy bottle
  • lavender flower heads in a glass jar and lavender essence in an opaque plastic squeezy bottle
  • oregano leaves in a glass jar and oregano essence or odiforous leaves in an opaque plastic squeezy bottle
  • cinnamon sticks in a glass jar and cinnamon essence or odiforous cinammon sticks in an opaque plastic squeezy bottle
  • garlic head in a glass jar and garlic essence or odiforous cut garlic bulb in an opaque plastic squeezy bottle
Procedure: 

Try to pair up each fresh with dried herb, or dried herb with herb essence, or 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.

Pair up fresh herb with smell of dried
Students smell the real herbs, by brushing their hands against them then smelling their hands.
Match with bags of dried herbs, whose identity is hidden (see photos).
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.

Each of the smells has many molecules making it up, but sometimes a predominant molecule that is responsible for the smell:
Oregano has the molecule carvacrol in its smell. Anise seeds have the molecule 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 smell molecules in mint and marjoram smells (see photo):
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.

Pair up plant part with smell of essence
Squeeze and sniff the smelly bottles (containing essences). Look at the plant pieces inside the glass jars. Match them up.
Students can also try and match each smelly bottle and jar of plant pieces with a picture of the plants they come from.

For younger students, duplicate the smelly bottles, and ask them to match up the ones that smell the same - use fruity smells too.
For very young students make into a game, where each table is a team. All tables are given the same-smelling tube at one time. The students at a table work together to try and guess what the smell is, and write it down. When the time is up, they hold up their written answer.

Optional for older students: which part of the plant dos each plant piece come from? (Leaves, flowers, seeds, bark or trunk?)
Coffee beans are seeds.
Cedar wood is the trunk.
Lemons are the fruit.
Lavender is the flower.
Oregano is the leaves.
Cinammon is the bark.
Garlic is the bulb (underground leaves).

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 taught: 
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7
Teacher: 
Christy Wong
Ingrid
Kecia Boecking
Self guided
Teaching site: 
McBride Elementary
New York Hall of Science
After School Program at Elementary schools in New York City
Science World
Van Dusen Botanical Garden
Activity originally developed and delivered: 

New York Hall of Science for herb essence and molecule smell match.
Van Dusen Botanical Garden Plant Colours and Smells family activities for dried and fresh herb smell match.