Directions for teachers

Partner students up. Ask them to watch the video “Movie S3” from the primary source article, “Harvesting of aerial humidity with natural hygroscopic salt excretions,” and answer the first question. Then have them read the Science News article “Salty sweat helps one desert plant stay hydrated” and answer the rest of the questions with their partner.

Directions for students

Working with your partner, watch the video “Movie S3” from the primary source article, “Harvesting of aerial humidity with natural hygroscopic salt excretions,” and answer the first question. Read the Science News article “Salty sweat helps one desert plant stay hydrated” and answer the rest of the questions with your partner. 

Videos as scientific data

1. Before reading the Science News article, watch the video “Movie S3” from the primary source article, “Harvesting of aerial humidity with natural hygroscopic salt excretions.” Discuss what you observe. What is changing?

The video is zoomed in on a green linear structure, and water or a clear liquid appears to be decreasing in volume over time around a white crystalline substance, which may be a salt. There also appears to be a bug stuck in the water.

2. After reading the Science News article, watch the same video again. Based on your understanding from the article, what do you think you see in the video?

Student answers will vary but should explain that water is evaporating and/or being absorbed by a plant and that salt secreted by the plant is crystallizing as the volume of water decreases. 

3. What type of video is it? Why do you think scientists chose to record that type of video?

Scientists recorded a time-lapse video. It allowed them to observe how the salt crystals on the plant interacted with water and changed over time.

4. What scientific question was materials scientist Marieh Al-Handawi investigating?

Marieh Al-Handawi was investigating whether the chemical composition of the excreted salts on the Athel tamarisk affected the amount of dew that was collecting on the plant’s leaves.  

5. Brainstorm another scientific question that this type of video could help answer. 

Student answers will vary. For this study, a time-lapse video could help scientists determine the time span over which the plant collects moisture. In other fields, time-lapse video could help scientists study patterns in ocean tides or animal behavior.

6. What is the relationship between the primary source article and the Science News article? Is it helpful to have access to both? Why or why not?

The primary source article is the scientific paper that the Science News article is reporting on. It’s helpful to read the Science News article because it summarizes the research study in language that is easy to understand. It’s helpful to see the scientific paper because it contains data, video clips, visualizations and the full explanation of the researchers’ results and ideas. The Science News article is too short for this and is intended for a lay audience, while the scientific paper shares details of the findings that will be useful to other scientists.

Drawing chemical adaptations

1. Draw a picture of the Athel tamarisk plant in its natural environment. Make sure your image indicates different aspects of the unique environment. Use figures in the primary research article or other sources to find the information that you need.  

Student diagrams will vary but should show a dry, arid environment, which may look like a desert. Student drawings should also indicate salt-rich soil conditions, potentially in a coastal flat. 

2. With your partner, discuss the plant’s adaptation that was studied in the article and talk about why it was beneficial to its survival. Write down your answers.

The Athel tamarisk plants excrete a mixture of salts. The salts allow the plant to harvest water from air at a lower humidity level than is usually possible for plants that use water-attracting leaf structures. This adaptation likely increases the Athel tamarisk’s likelihood of survival in a dry, arid environment. Students may also indicate that the composition of the plant’s salt excretions may depend on the salts available in the soil. 

3. Draw a molecular diagram of the interaction between the salts and the water from the humidity in the air. Use your knowledge of the composition of the salts, or ionic crystalline substances such as sodium chloride, gypsum and lithium sulfate, named in the article. Feel free to look up information as needed.  

Student diagrams will vary but should show the ions or chemical composition of the salts on the surface of the plant leaves and how water molecules from the air are attracted to the ionic compounds. The oxygen atoms in the water molecules will be attracted to the positively charged ions in the salts, and the hydrogen atoms in the water will be attracted to the negatively charged ions in the salts. Then, water’s hydrogen atoms will be attracted to the oxygen atoms of other water molecules, eventually creating water droplets that dissolve the salts. 

4. Using your knowledge of intermolecular attraction and electrostatic, or Coulombic, attraction forces, explain why this plant adaptation might be more successful at collecting water from the air than an adaptation related only to leaf structure.

In ionic crystalline substances, or salts, atoms have gained or lost electrons through bonding to create positive or negative ions. Water, or H₂O, is a covalently bonded molecule with a partial negative charge on the highly electronegative oxygen and partial positive charges on the two hydrogens. The partial charges in water molecules would likely be attracted more strongly to the full charges on the ionic solids than to other partial charges within a leaf, which is likely composed of mostly covalently bonded, or organic, molecules. Therefore, when water molecules from the air bump into the salt crystals, they may be more likely to cluster around them than if they bumped into a bare leaf.     

5. Explain why you think the humidity level would impact the amount of water that could be collected on a plant. Draw a quick diagram using water molecules to represent two different relative humidity levels: 50 percent humidity and 80 percent. Why might this plant harvest more water at lower humidity levels compared to other plants that lack this adaptation?

Lower humidity means there are fewer water molecules in the air than at a higher humidity, so fewer collisions and opportunities for attraction would occur between water in the air and the plant leaves. If there is a more electrostatically attractive substance on the leaves, it’s more likely that water would stick to the plant leaf at lower humidity levels.  

6. What other questions do you have about how the Athel tamarisk uses this process to get water?

Student answers will vary but questions may include: How does the plant take in the water from its surface? How much of the water that the plant adsorbs is lost to evaporation? What other plants might use a similar strategy and how might their approach differ from this plant?