Food Chains and Food Webs
Lesson 18 of 23
Objective: Students will know what energy pyramids are and how these models are used to quantify the flow of energy through trophic levels in ecosystems.
Begin with the question, “What is the ultimate source of energy for all life on Earth?” Allow 2-4 students to respond. If differing answers are given, allow students to engage in academic discourse. Act as a facilitator for the discussion. Ensure that the discussion ends with the correct response clearly communicated.
Introduce New Material
Begin by watching a few clips from the Life video series, Life Challenges (or another equally engaging video). Allow students to view 2-3 instances of predator –prey interactions before stopping the movie and asking students to predict what we will be talking about today. Students will likely identify that the lesson involves predators and prey but listen for the student who may indicate that the lesson is about food chains or food webs. Once this stated, ask students, “What travels through food chains or webs?” This question allows students to get to the “point” of the lesson. They might begin with responses like, “food, or water” but eventually someone will correctly identify that energy travels through a food chain.
Introduce the new vocabulary: consumer, ecosystem, equilibrium, food chain, trophic level, population, predator, prey, producer, autotroph, biomass, heterotroph, consumer, primary, secondary, tertiary, quaternary, herbivore, carnivore, detritivore, omnivore, decomposer, and food web. As always, identify those terms with prefixes, suffixes, Greek or Latin root words. Instruct students to add those terms to their Vocabulary Map, an ongoing record of root words and prefixes/suffixes that will help students build their vocabulary and increase literacy. The student example shows how it used.
Inform students that organisms all have roles in the environment. Ask students what role plants play in the environment. Cue them to use the warm-up question as a clue to answering the question. Listen to their comments see if they are able to identify plants as the first organisms to transfer energy from the sun. Listen to students’ responses to the question and emphasize that plants are producers or autotrophs that make their own food.
Introduce the term, consumer. Ask students, “What does it mean to consume?” Listen for responses that indicate that students know that to consume means “to eat”. Remind students that producers, on the other hand, “produce” their own food. Use the terms autotroph and heterotroph interchangeably with the terms producer and consumer so that students will learn that the terms are the same.
Display visual information as you teach and instruct students to take notes using guided notes that you have provided or use a note-taking strategy that you have taught. Guided notes provide greater support for the different learning styles of students.
Make frequent checks for understanding throughout the teaching and note-taking process to identify gaps in students’ understanding of concepts. Ask questions like:
- What is an herbivore?
- How are detritivores different from decomposers?
- What is used to indicate the flow of energy in a food chain or web?
- What do the arrows in a food chain represent?
- What happens to energy as we move from step to step in a chain or web?
Walk around the room to ensure that students are writing down the correct information. At the end of the lesson, allow students to participate in a game, Food Chain Hollywood Squares. This activity helps students reflect on their own learning and also serves as a formative assessment.
Inform students that they will complete a “gizmo” today, using the Explore Learning technology. Gizmos are computer simulations that help students see science in action. The technology is great for helping students take abstract concepts and make them more concrete using hands-on computer based lessons.
Issue the computers so that students have them before you model use of the site for the lesson. Instruct them to log in and access the main site.
Note: Explore Learning is an inquiry-based learning system using online simulations. My school district subscribed to the service a couple of years ago and I have found the lessons to be highly effective in helping my students grasp science concepts. Sign up for a free trial if you are interested in accessing the resources and student exploration worksheet (Food Webs and Food chains) associated with this lesson.
Walk around to monitor that all students are on task, able to access the site and log in with their individual user names. Identify 2-4 students who are skilled computer users and utilize them as a resource to assist other students who are not. Once it is determined that all students have accessed the site, model how to access the lesson and navigate the gizmo. Instruct students to watch and perform each action that you take, using the computers they have at their desks.
Decide beforehand if you will provide copies of the worksheet or if students will complete and submit electronic worksheets. Some students work best with hard copies so make the determination in advance of who will need a hard copy and have copies available for those students. If you decide that students can complete the assignment online, model how to download a “word” copy, type their answers onto the worksheet and submit the assignment electronically.
Point out the vocabulary that is associated with the lesson and answer the “Prior Knowledge Question” as a class, taking responses from 1-3 students to develop an answer for the class. This allows you to hear students’ reasoning, as a formative assessment and it allows everyone to start at the same point once you release them to work independently. If students struggle with the question, spiral back and reinforce key concepts before proceeding.
Model 1-2 of the gizmo warm-up activities for the class. The gizmo warm-up is intended to help students learn how to navigate the controls for the lesson that follows. As you complete each action, instruct students to use their computers to perform the same action. Release students to complete the warm-up activity as you walk around to ensure that everyone is able to navigate the controls for the lesson.
Instruct students to work independently on the computers to complete all parts of the assignment and assessment that follows the simulation. Instruct students to drop the completed gizmo in Edmodo when they complete the assignment or instruct students to complete a hard copy that you provide. Based on students’ particular learning needs and abilities, determine which students will submit electronically and which will not.
Note: Edmodo is a great FREE teacher website that allows teachers to load assignments, send reminders and schedule important dates for students and their parent/guardian to access outside of class. Students join a class that is set up by the teacher and are then able to submit assignments directly to the site. Edmodo also allows students to take quizzes and engage in topic-based chats, as well.
Submission of this assignment electronically serves two purposes. First, utilizing Edmodo helps students learn how to attach and send files electronically. By submitting assignments through Edmodo, students learn how to upload files (a skill they will need as they advance in their high school classes). Second, electronic submission of assignments saves a lot of paper and reduces the amount of time needed to make copies of multi-page documents.
Alternatives to electronic submission include, instructing students to send the completed assignment to a designated email address. If computers are not available in the school setting, instruct students to access a computer outside of class (a local library) to complete the assignment. A lack of computers in the school setting should not be a deterrent to students’ use of technology. Encourage students to utilize available resources in the community ( public libraries) to enhance their technological skills and abilities.
After the completed assignments are received, review the written responses to determine how well students are able to use the simulation to draw the correct conclusions. Look for students’ ability to correctly use the table in #3 to predict how different consumer groups are affected as the environment changes. Then, look at question #7 to assess how well students reason and draw a correct conclusion about what effect a removal of prey would have on an ecosystem. Lastly, assess how well students are able to analyze the data to explain why the population of each organism changed the way it did. One student provided a more complete answer than the other. But, both responses indicate that the students possess a conceptual understanding of the relationships in a food chain.
Also, in an effort to help students build their writing skills, check the responses for correct grammar and spelling. These are not factors for which you need to deduct points but corrective feedback regarding grammatical errors reinforces the need for sound writing practice across the curriculum.
Ask, “What organism is always the first organism in a food chain or food web?” “Why is this important?” These type of open-ended questions encourage students to respond and explain their thinking.
Instruct students to discuss their response with someone in front of or behind them. Walk around and listen to students’ conversations. Correct misconceptions that are overheard and remind students to use the language of the lesson in their responses. Resist the urge to give answers or explanations outright. Use inquiry- based questioning to help guide students to the correct thinking that leads to the correct response.
Based on what is heard in the conversations around the room while walking around, decide whether the learning targets have been met. If students are able to correctly identify that producers are the first organism in a food chain and that producers absorb sunlight energy to make food, the learning targets have been met. If most students ae having difficulty engaging in content strong discussions around the questions, plan to revisit the lesson key points at the start of the next lesson.