Our Lungs Our Air Our Health
Activity 5 (Explore): Seeing Ozone's Effects on
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In this activity, students examine ozone damage to leaves as a way to understand what happens to human lungs from exposure to ozone.
Activity Objectives & Materials
Approximate Time: 45-60 minutes
Students will understand that gases in the air (ozone in particular) can damage the delicate parts of living things
Ozone damaged-leaves (pictures or actual leaves)
Leaf underside wet mount slides (optional)
Projector & speakers
Leaf investigation lab sheet
DCI: LS 2.A: Interdependent Relationships in Ecosystems
SEP: Constructing Explanations
CCC: Cause & Effect
We know that Tatiana and Calvin have trouble breathing sometimes. It is worse when they exercise, and it’s also worse when they’re outside a lot. Why do you think this is?
Guide student discussion around the idea that environmental factors (like pollen, dust, air pollution, etc.) can affect our respiratory system.
1. Frame the Activity
Tell students that when scientists identify an “effect” like an asthma attack, they are often curious about what is causing it. Remind students about Activity 1 when they discussed what might be causing Tatiana and Calvin’s asthma attacks, and what might be causing asthma rates to be higher in some places. If they think that something in the air is causing it to be harder for Tatiana and Calvin to breathe, then they need to learn more about how things in the air affect living things. They can’t cut open Tatiana’s lungs, so instead they’re going to look at plants to see how gases in the air affect them. Hand out the Leaf Investigation Lab sheets to students.
2. Introduce Ozone-Damaged Leaves
Show students what ozone-damaged plant leaves look like. You can do this by taking them outside, bringing leaves inside, or showing them pictures like the tulip poplar leaf below.
Have students make observations of what they see and write them on the observation (right) side of their sheets.
3. Ozone Damage Discussion
Ask students if they think the leaves are heathy. Why or why not? (you may want to show them healthy leaves for comparison). Ask students if they think the spots are a cause of something or an effect (they should say effect). Have them write “effect” on their papers next to where it says “observations.” Then ask them what they think might be causing this effect. Have them write the potential causes on the “cause” side of their sheets. These don’t need to be correct (they should be hypotheses such as acid rain, insects, diseases, etc.). Ask students if they think gases in the air can cause damage like this.
4. Take A Closer Look
Tell students that you are going to look more closely at the cells on the underside of the leaves. If microscopes are available, have students look at peelings from under the leaves. If not, show them photographs of the undersides of the leaves through a microscope like the one shown below
Have students write their observations in the space on their lab sheets. Make sure students see and describe the stomata (little “mouths” on the leaf undersides).
Teacher Tip: This part of the activity is a another good place to reinforce students’ understanding of cells, and where they fit into the hierarchy of cells-tissues-organs-organ systems. You can also make a connection to red blood cells, which students learned about in Activity 3,
5. Stomata Discussion
Ask students a variety of questions to help them build understanding of stomata. Students may want to take notes on their lab sheets. Possible questions & answers:
What do stomata look like? (they look like lips, little mouths, donuts, etc.) NOTE: the stomata are the pores (the holes) in the middle. The “guard cells” are the sides.
What structure is a stoma made of? (it is a hole with two curved cells on the sides).
What do you think the function of a stoma and guard cells is? (to let things in and out of the leaves, and to keep things from getting in or out when they close)
What do you think can get in and out of the undersides of leaves? (gases like oxygen, carbon dioxide)
What gas do plants need to grow? (Carbon dioxide)
Teacher Tip: Don’t get bogged down in teaching students about stomata. The goal here is to help them understand that ozone can damage the inside of living things
6. Return to Cause and Effect
Go back to students’ original hypotheses about what might be causing the damage to these leaves. See if they have a better sense of what the correct cause is and why other causes are unlikely (ex. insect damage looks like little bites taken out of leaves). After discussion, tell students that damage like this is caused by something getting inside the leaves. In this case the leaves have ozone damage. Ask if any students have heard of ozone before.
7. Ozone and Plants Reading
Have students read the paragraph about ozone on their handout and answer the questions below the text. Answers:
Ozone is a gas
Ozone near the surface is harmful to living things
Ozone high up in the atmosphere is good for living things
Ozone prevents plant leaves from performing photosynthesis well
Additional media: In the fluorescence photograph shown, the plant leaves on the right were grown with elevated ozone levels, and the leaves on the right were grown under normal conditions
Source: Originally Kim, M.S., McMurtrey, J.E., Mulchi, C.L., Daughtry, C.S.T., Chappelle, E.W., and Chen, Y.R. Steady-state multispectral fluorescence imaging system for plant leaves. Applied Optics, 40:157-166. 2001; reprinted in NASA Earth Observatory
To read more about the research behind this photograph, check out this article where it appeared on NASA's Earth Observatory website.
8. Ozone Gardens Video (optional)
9. Connecting the Dots: Trees, Lungs, and Ozone Damage
Show students the picture below and ask them what they see. They will likely say this is a tree, but it’s actually an upside-down casting of human lungs.
Take a moment to point out to students where the trachea, bronchi, and alveoli are in the casting. Ask them where in the picture oxygen goes from the lungs to the circulatory system (at the very tips of the bronchioles, where the alveoli are). Then have them think about a tree. Where does the carbon dioxide and the oxygen come in and out of trees? It is in the leaves, which are at the very tips of tree branches. Ask students when it comes to breathing, how are human lungs like trees?
Focus the discussion to reach these key points:
Both trees and human lungs take in and releases gases they need to survive.
Both trees and human lungs transfer gases at the tips of long “branches”.
Next, ask students how human lungs are different from trees when it comes to breathing. Focus the discussion to reach these key points:
Trees take in and release gases directly from their leaves. Humans need to breathe the gases into their lungs first from outside their bodies.
Humans have alveoli where the gases are transferred in and out. Trees have stomata where gases are transferred in and out.
Finally, remind students where the ozone damage is in trees. Then have them consider where ozone damage might be in a human. Give them time to discuss with a partner before moving to the formative assessment.
Clarification: There are many similarities and differences between plant leaves and human lungs, especially the fact that they are where the organism has maximum surface area for gas exchange. Use the analogy to foster student understanding, but don’t push it too far because it will get unnecessarily complex and may lead to students misconceptions.
Extension: If time permits, have students make a Venn diagram showing how trees and human lungs are alike and different in terms of how they take in and release gases they need to survive.
10. Return to the KWL chart
Have students take out the KWL charts they created in Activity 1 and display the class KWL chart you made. Have students identify anything new they’ve learned that helps them to understand the phenomenon. For example: your heart rate and your breathing rate are connected. Add any new learning to your chart while they add it to theirs.
11. Formative Assessment
Have students write a hypothesis based on what we learned today about why they think Tatiana and Calvin have a hard time breathing when they go outside. Their hypothesis should include something about how gases (like ozone) can affect the insides of living things. Key points:
Tatiana and Calvin may have irritated or damaged lungs because of ozone. Ozone is a gas that is a kind of air pollution. Ozone can get into living things and damage them. If it got into Tatiana and Calvin’s lungs, it may be hurting them.
Differentiation: Discuss the formative assessment question before having students write out their answers.