SF Fig. 2.15.1. The nostrils of a blacktip reef shark (Charcharhinus melanopterus) are visible (forward of the eyes) as researchers measure the shark during a feeding study.
Image by Kanesa Duncan Seraphin
Title
Weird Science: Compare Your Sense of Smell to a Shark’s Sense of Smell
NGSS Science and Engineering Practices
NGSS Crosscutting Concepts
Table of Contents
Sharks are predators with extraordinarily acute senses that allow them to detect and track wounded or dying fish. Sharks often select weak, sick, or injured prey because they are easier to catch than healthy prey. A shark’s nostrils, or olfactory organs, help a shark smell their prey (SF Fig. 2.15.1).
The concentration of an odor in water is measured in parts per million (one odor molecule for every million molecules of H2O). Sharks can smell blood from hundreds of meters away—in concentrations as low as one part per million (ppm).
One part per million (ppm) is the same as
- one inch in 16 miles,
- one minute in two years,
- one pinch of salt in 2,000 pounds of potato chips, and
- one cent in 10,000 dollars.
Compare your sense of smell to that of a shark.
Materials
- Eight identical clear cups
- Permanent marker
- Tap water
- Large measuring cup, marked in mL
- 5 or 10 mL measuring spoon
- Spoon or stir stick
- Tomato or lemon juice
Procedure
Safety Note: Use food-safe cups and spoons that have not been used with laboratory chemical or biological substances.
- Label the cups one through seven.
- Use the measuring cup to carefully measure 90 mL of water into the cups numbered two through eight.
- Use the measuring cup to measure 60 mL of tomato or lemon juice into cup number one.
- The tomato juice represents blood from a wounded fish.
- The lemon juice represents bodily fluids that a shark might smell in the ocean.
- Use the measuring spoon to transfer 10 mL of the juice from cup number one into cup number two. Mix cup number two well.
- Repeat this step until you have put 10 mL from cup number six into cup number seven.
- Cup number eight is your control; this cup only has tap water in it.
- Starting with cup number eight, smell each of the cups to see when you are able to detect the juice in the cups.
- (Optional) Use your other senses to make observations about the liquids in the cups as instructed by your teacher. Two examples of observations are listed below.
- Look at the appearance, or color, of the solutions by drawing circles and coloring them with a crayon to correspond to the color in each cup. You can look at paint swatches to compare colors. To observe the color of the liquid in the cup, you may have to put a sheet of white paper under the cup.
- Take a small sip of the liquids from each cup, starting from cup eight.
Question Set
- At what cup number did you start to smell the juice? Use SF Table 2.1.1 to determine how good your sense of smell is using parts per notation.
- Some sharks can smell blood concentrations as low as one part per million (ppm). How does your sense of smell compare to a shark?
- (Optional) At what cup number did you observe a difference in the color of water (compared to tap water, cup number eight)? At what cup number did you observe a difference in the taste of the water (compared to tap water, cup number eight)?
| Cup Number | Concentration |
|---|---|
| 2 | 1 part in 10 |
| 3 | 1 part in 100 |
| 4 | 1 part in 1,000 (ppt) |
| 5 | 1 part in 10,000 |
| 6 | 1 part in 100,000 |
| 7 | 1 part in 1,000,000 (ppm) |
| 8 | N/A (control) |
