Chapter 9 Lesson 1, "Gases in the Atmosphere"

Materials:

• Worksheet, "Gases in the Atmosphere"
• Optional Worksheet, "Surveying Air Quality"

Objective:

• Students will identify the gases in the atmosphere.
• Students will describe the oxygen-carbon dioxide cycle.
• Students will describe the nitrogen cycle.

Anticipatory Set:* At least 30 minutes prior to class the teacher will cut and apple into three or four pieces. Put all but one piece in a plastic bag. Leave one exposed to the air. When students come in explain to them what you did. Next ask why they think the one piece of apple is brown. Have them hypothesis what will happen if you remove another piece from the bag. Reexamine the piece after 5 or to minutes.

Apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The oxidation reaction basically forms a sort of rust on the surface of the fruit. You see the browning when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals.
The reaction can be slowed or prevented by inactivating the enzyme with heat (cooking), reducing the pH on the surface of the fruit (by adding lemon juice or another acid), reducing the amount of available oxygen (by putting cut fruit under water or vacuum packing it), or by adding certain preservative chemicals (like sulfur dioxide).
On the other hand, using cutlery that has some corrosion (as is seen with lower quality steel knives) can increase the rate and amount of the browning by making more iron salts available for the reaction.

Teacher Input:* What do you need most in order to survive? If you take this away you would die within just a couple minutes. What do you call the air that surrounds the earth? How much of the atmosphere is oxygen? Many different gasses are found in the atmosphere. Have the students name as many as they can while the teacher lists them on the board. Next ask the students what the most common gas is in the atmosphere. What is the third most common? Show the students this pie chart of the composition of the atmosphere. (1, 2)

Does the composition of the atmosphere change? How do we know. (ice core sample 1, 2, 3)

Explain how a lot of gases move in and out of different organisms places in the atmosphere. Show the nitrogen cycle. explain how most nitrogen compounds are produced by bacterial action 90% Some other nitrogen compounds can be produced by lightning. As it passes through the air molecules of N2 are broken apart and then the nitrogen is free to react with other types of molecules. The rain then washes these compounds down into the soil where it can be taken up by plants.

Explain the oxygen cycle. What process turns carbon dioxide into oxygen? Why is the sun in the picture? What process turns oxygen into carbon dioxide?

Guided Practice:* Go through the questions with the students on page 207. Give one question to each site.

Independent Practice:* Students will complete the Gases in the Atmosphere worksheet.

Check for Understanding:* Students will complete a quiz on Lesson one, Gases in the Atmosphere.

Duration:

30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).

Alaska Content Standards Addressed in this lesson:

• SCI A-1 Students will understand models describing the nature of molecules, atoms, and sub-atomic particles and the relation of the models to the structure and behavior of matter (Structure of Matter);

• SCI A-15 Students will use science to understand and describe the local environment (Local Knowledge); and: