Relato de la sesión de prueba y feedback del alumnado

3. Let students follow the procedure step-by-step and to answer guide questions.

4. Note that the graph does not contain information about the gases that make up each layer in the atmosphere. Students can get these information from the description of the layers in the text. To put the information together, let students organize the data from the graph and the text that describes the features of each layer. They will then be able to compare the layers of the atmosphere and tell the basis for dividing the layers. Making a table to organize data about an event or phenomenon from varied sources is also a higher- order thinking skill.

What is the basis for dividing Earth’s atmosphere into layers?

Activity

1

Grade 7 Science: Teacher’s Guide (Second Part) 101

Grade 7 Science: Earth and Space 232

Answers to Questions in Activity 1

Q1. Based on the graph, the five layers of the atmosphere starting from the ground or Earth’s surface are: troposphere (about 10 km), stratosphere (about 40 km), mesosphere (about 30 km), thermosphere (about 415 km), and exosphere (cannot be determined from the graph).

Q2. In the troposphere, the temperature decreases as the altitude (height of the atmosphere) increases.

In the stratosphere, at heights around 10-20 km above the ground, the temperature is almost the same. From about 20 to 50 km above, the temperature increases.

In the mesosphere, the temperature decreases as height increases.

In the thermosphere, from heights about 87 to 100 km, the temperature change is small; it increases gradually from about 100 to 110 km. From 110 km to the end of the layer the temperature steadily increases with height.

The gradual increase in temperature with altitude continues to the exosphere.

(_Note: Though it is not necessary to explain to students at this point the reason for the variation in temperature, it is good for you to know that these variations are due to changes in the chemical and physical characteristics of the atmosphere with altitude.)

Q3. In the lower part of the stratosphere, the temperature increases with height. The same is observed starting from the thermosphere up to the exosphere.

Q4. In the troposphere, the temperature decreases as height increases (from about 15 degrees Celsius to minus 45 degrees). A mountain climber will feel the temperature difference as he or she moves from the ground, up. The temperature also decreases in the mesosphere (from minus 5 to about minus 90 degrees Celsius).

Take note that the temperatures are global averages. The atmospheric temperature of countries above the poles is different from the temperature above the equator.

Q5. (Let students repeat the trends described above.)

Q6. The layers of Earth’s atmosphere is divided based on temperature differences

Q7. Overall, the graph shows that the closer the atmospheric layer is to the Sun, e.g. thermosphere and exosphere), the hotter the temperature.

However, if one studies the temperature in the lower layer, the reverse trend is observed. For example, in the troposphere, the temperature close to Earth is higher than the temperature above the ground. Ask students to guess what the reason is.

(FYI: The main reason why temperature decreases with altitude in the troposphere is that it is heated from below. The atmosphere is predominantly transparent to sunlight, so the Sun heats the ground directly. The ground warms the bottom layers of the atmosphere by radiation and by convection. This will be discussed in the next section.

The situation is like water heated in a pan on the stove--the water is hottest at the bottom and coolest at the top.)

In general, the variations are also due to changes in the chemical and physical characteristics of the atmosphere with altitude. However, students may not yet be ready to discuss this.

Q8. What other information about Earth’s atmosphere can you derive from the graph?

Let students notice the zigzag portion on the vertical axis (thermosphere layer). Let them explain why this is not a straight line.

A sample table of data about the Earths’ atmosphere may look like

The students are now ready to study some global atmospheric phenomena.

Grade 7 Science: Teacher’s Guide (Second Part) 103

Grade 7 Science: Earth and Space 234

What is the Greenhouse Effect?

The most abundant gases in the Earth’s atmosphere are nitrogen (78%) and oxygen (21%). The remaining 1% is a mixture of carbon dioxide, water vapor, and ozone. These gases not only produce important weather features such as cloud and rain, but also have considerable influence on the overall climate of the Earth, through the greenhouse effect and global warming.

In the Philippines, greenhouses are used by commercial plant growers or plant lovers. If there is a greenhouse in your locality, use it as a springboard for the lesson. Introduce the concept of greenhouses by asking students what they know about it.

Teaching Tips

1. A week before the lesson, ask students to gather 1.5 L or 2.0 L softdrink plastic containers. Use these to construct your own model greenhouse while students do their own. Then try out the activity before you ask students to do it.

2. Each group needs two thermometers. If thermometers are not enough for, say, six groups (12 thermometers are needed), have at least two pairs of setups to allow comparison of data. Check the thermometers first if they are working before distributing to students.

3. The activity procedure is easy to follow. Put the setups in diffferent locations. The temperature readings reported in different locations might not be the same. What is important is that the temperature in the bottle with windows is lower (cooler) than the temperature in the bottle without. They should be able to derive this information from the activity. Use the result of the activity to introduce the greenhouse effect clearly stating what bottles A and B represent.