Chapter 12 Lesson 2 "Food Chains and Food Webs"

Materials:

• Lesson 2 scramble
• Food Chains and Food Webs
• A Food Chain Lab (Optional)

Objective:

• Students will distinguish between producers and consumers
• Students will trace a food chain from producer through three levels of consumers
• Students will explain how a food chain is related to a food web
• Students will understand the importance of decomposers in communities.

Anticipatory Set: Students will be shown three organisms on a computer screen. Students will explain which organisms eat the other organisms. After the students give this information the instructor will then add other organism to the picture to form a food web by removing the black square. Here is the image to start with if you have Photoshop or Fireworks you will be able to move the different pieces around on the computer screen.

Teacher Input: Teacher will introduce two types of food chains. The first is a bear food chain that is comprised of links of fish. The second is more of a circular food chain that shows a cat at the top but then it becomes food for decomposers. The teacher will explain both food chains while using the terms food chain, producer, and consumer. There are different types of consumers. Show the students a picture of a herbivore and explain that some consumers eat only plants, sum such as this wolf eat only animals, and others will eat almost anything and are known as omnivores. omnivore 2.

The teacher will then pose the question, "As you move from one level of the food chain to the next does the number of organisms increase or decrease?" Here is an example. If the students look out there window they may see hundreds of willow trees. They have to look harder to find moose feeding on those willow trees. There may be one moose for every 10,000 or more willows, further still there may be only a few wolves for every 100 moose calves. This is known as the Pyramid of numbers. Explain it further to the students using this diagram.

In the beginning of class you took a food chain and added more organisms to make it very complicated. Show them the thing they created at the beginning of class. When all the food chains in a community are linked like this it is known as a food web. Here are some different types: discuss them with your students: Arctic Marine, boreal forest, grassland. Ask, "Why do consumers usually eat a variety of foods and not just one particular thing?

Most of this lesson we have looked at energy and materials moving up a food chain. What happens when it gets to the top? Does it all just get stuck? Show the students this picture and explain the role of decomposers.

Guided Practice: Students may complete their lesson 2 Scramble while the lesson is being taught.

Independent Practice:Students should complete Food Chains and Food Webs and Read Lesson 2 from pages 306-310. If time permits students have the opportunity to complete the Lab, A Food Chain Lab (Optional).

Check for Understanding:Students should take the quiz on lesson 2.

Duration:

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

Alaska Content Standards Addressed in this lesson:

• SCI A-9 Students will understand the transfers and transformations of matter and energy that link living things and their physical environment, fro molecules to ecosystems. (Flow of Matter and Energy)
• SCI A-14 Students will understand
  • the interdependence between living things and their environments:,
  • that the living environments consists of individuals, populations, and communities: and
  • that a small change in a portion of an environment may affect the entire environment (Interdependence);

• SCI A-15 Students will use science to understand and describe the local environment (Local Knowledge);
• SCI D- 1. apply scientific knowledge and skills to understand issues and everyday events;