Unit 4: Light at the Head of the Food Chain January 7, 2002
Preparation
 Objectives
  • Explore the role of light in photosynthesis.

  • Explain how light energy is converted into chemical energy.

  • Describe the role of plants (producers) in the food chain.
Vocabulary Preview
  • electrons
  • food chain
  • herbivore
  • photons
  • photosynthesis
  • producers
  • trophic level
Materials
  • No special materials required.
Suggested Time

The unit is divided into two class periods. Allow approximately 20 minutes for each online SimLibrary activity.


Feature Article
Winter Light

Teacher Resources
Overview
Unit 1:  Nature of Light
Unit 2:  Visible Light & Color
Unit 3:  Light & Matter
Unit 4:  Light at the Head of the Food Chain
Unit 5:  Light: A Literary Approach
Glossary
Web Links
Class One:
Light in Photosynthesis

1) Show students a photograph full of plants, such as the one included below. Write on the chalkboard the statement, "This photo represents a power plant." Ask students to explain the statement.

2) Sunlight (photo) + food production (synthesis) = photosynthesis. Define photosynthesis: the conversion of the Sun's energy into chemical energy found in carbohydrates. Ask students to refine the explanations given in #1.

3) Light is a key ingredient in photosynthesis. The energy from photons of visible light promote electrons to a higher energy level in atoms. (See Unit 1: Nature of Light).

4) For ideas about teaching about the absorption spectra, see Unit 2: Visible Light and Color, Class Two: Colored Light.

Related Activities
An Overview of Photosynthesis
 Students can do this activity to learn about the importance of the photosynthetic process.
The Role of Light in Photosynthesis
 This activity enables students to follow the changes in the rate of photosynthesis over a period of a day.
Light Dependent Reactions in Photosynthesis and
Calvin Cycle Reactions in Photosynthesis
 High school biology students can do the more in-depth activities to explore the inputs and outputs of the light reactions, including the role of ATP and NADPH. In the second activity, they examine the light-independent reactions in photosynthesis.

Class Two:
Plants in the Food Chain

1) Ask the vegetarians in the classroom what percentage of their diet is supplied directly by plants. Ask them what percentage of their diet is supplied indirectly by plants. Ask the carnivores the same two questions.

2) Define food chain: an illustration of feeding relationships in an ecosystem using a single representative for each of the trophic levels. Ask students what species are in the bottom rungs of the food chain. Ask if they can explain why.

Explain that plants are the bottom rung in the food chain. They are known as producers because they produce food via photosynthesis for the herbivores (plant eaters) in the chain. Carnivores higher up the chain eat prey, who might be dependent on the producers. If there were no plants turning sunlight into chemical energy, there would be no food to feed the animals (and humans) of the world.

3) Have students summarize the relation between light and the food web by drawing a schematic of the pathway of light from the Sun to the fried chicken on their dinner table.

Related Activities
Exploring Food Chains and Food Webs
 This activity introduces food chains and how populations in an ecosystem affect one another. They describe the effects using a graph of population vs. time.
Enter Predator
 This activity introduces trophic levels in a food web. Students explore the relative biomass ratios of producers, primary consumers, and secondary consumers in the food pyramid.