Ecosystems Curriculum

Section 4: Lesson Plan — Using Time-Lapse Video to Reveal the Cycle of Decay

Materials

• Time-Lapse Video

Prep Step

• Review understanding goals and background information.
• Read the lesson plan.
• Either download the video or arrange to show them to students on-line.
• Set up a VCR and television monitor for viewing the time-lapse clips.

Analyze Thinking

Step 1: Gather Students' Ideas and Questions

Many people don't realize that organic matter is recycled. Ask: "What are some of the reasons that it is hard to realize that matter is recycled?" Collect ideas. If no one introduces the issue of time, bring it up.

Ask, "How long do you think it takes for something to decay? ...a few days? ...a week?" Explain that it takes time for decay to occur. Just how quickly depends on the conditions for decay. Think about how quickly things "spoil" in the summer. What about it the winter? Gather students' thoughts about differences in how long in takes for something to decay in summer versus winter. Explain that the process of decay can happen so slowly and gradually that sometimes people may not notice that it is happening—that a fallen log, for example, is rotting and actually turns into a part of the soil that can be used by plants to grow.

RECAST Thinking

Step 2: Explain the Time-Lapse Decay Activity

Tell your students that you are going to see some film footage that shows decay happening over time. The films have been accelerated to show decay happening at a much faster pace than normal.

Step 3: View the Time-Lapse Videos

Show the first few moments of the film. Stop the film. Ask, "What do you predict will happen to the strawberries that look normal and ripe?" Gather ideas.

Tell your students to watch carefully to what happens to the strawberries. Discuss what is occurring and how it happens. Make sure the students realize that eventually the decaying fruit turns into part of the soil. Explain these videos were captured over time and that normally decay happens slowly and gradually so the process is sometimes not noticeable until the object is visibly moldy or rotten. However, microbes are all around, all the time, feeding on dead matter and doing their job, which is decomposing matter and recycling it.

Explore Causality

Step 4: Time Delays Make it Hard to See Causal Patterns

Explain to your students that it can be hard to detect the cause of something when there is, or appears to be, a long time delay between cause and effect. Not noticing effects because of time delays is especially a problem when considering how we interact with our environment. Offer a few examples:

• In Florida, lots of water was used to irrigate and grow sugar cane. It lowered the water table and then suddenly, sink holes started appearing, and the fresh water became brackish. This means that it mixed with salt water. This water is "toxic" to sugar cane.
• Nitrogen used to be an ingredient in detergents. However, when the detergent in untreated waste water gets into natural bodies of water, this nitrogen, which is also a fertilizer, accumulates and causes algal blooms, which throw the ecosystem out of balance and cause fish to die.
• DDT is a chemical that in small quantities does not appear to hurt anything. However, when amounts of it build up in the environment, its damaging effects become clear. When birds eat enough bugs poisoned with DDT, the shells of their eggs become too thin and baby birds die, lowering the size of some bird populations. After this was discovered, DDT was banned.

Ask students if they can think of any additional examples. Collect students' ideas and discuss.

Step 5: Show How Time Delays Affect Our Ability to Think About Decay

Explain that time delays also make it harder to realize that decay is going on. It is harder to understand the cyclic pattern because of time delays and causes that can't be seen. It can be hard to imagine that a piece of fruit or a bunch of leaves can become part of the soil. Have students think back to their own ideas before this unit. Ask them the following questions:

• Did you realize that decay is cyclic? What did you think?
• Did you realize that decay is going on all of the time?
• Did you realize how important decay is to an ecosystem?

Students can answer these questions on paper or in their journals.

Explain that cycles of decay are happening all the time. Even though it takes a long time, matter is always being broken down. Usually we only see different points in the process but cannot observe the process over time. By speeding up the decay, it is easier to see the portion of the decay cycle that goes from dead matter to soil. The results of the decay process help green plants grow.

Review, Extend, and Apply

Step 6: Review the Understanding Goals

Discuss the Understanding Goals with students to be sure that they understand them.

Step 7: Extend the Concept

Ask: "What would happen if things decayed very quickly? How would things be different? Think about the tropics where things decay much more quickly as an example." Gather students' ideas.

Why would organisms decay faster in places like the tropics than in places like New England? Tropical rainforests are moist and very warm, two conditions that support decay and decomposition. In New England, the weather can be very cold and dry. This slows decomposition. Think about your bathroom when you take a shower. The hot, moist conditions are perfect for mold to grow. It's the same way in rainforests. Here's a comparison to illustrate their difference: A leaf on the rainforest floor takes about six weeks to decompose, but a leaf in a New England pine forest takes about SEVEN years!