The Food Web

Unit 4: Ecosystems

Lesson 2: Exploring Ecosystems- Food Web

5E Lesson Planning:

I plan most of my science lessons using the BSCS 5E Lesson Model: Engage, Explore, Explain, Elaborate, and Evaluate.For a quick overview of the model, take a look at this video.

I use this lesson model because it peaks the students' interest in the beginning during the "Engage" portion and allows for the students to actively participate in the investigations throughout the subsequent steps. The “Evaluate” component of the 5E Lesson Model can be used in many ways by the teacher and by the students.

A great resource for lesson plan frameworks and explanations is the Community Resources for Science. The 5E Lesson Planning sheet and 5E Lesson Prompts come from this website. 

Unit Overview:

In this Unit students will learn about ecosystems and the transfer of energy through ecosystems. The lessons in the unit are primarily based on our local ecosystem- the Santa Monica Mountains. This area is known as a Mediterranean Ecosystem or Biome and we will learn about the plants, animals, climate, and human impacts on this area. 

Lesson Overview:

In this lesson, students will create Food Webs based on the previous lesson's Food Chains that they created. They will also make a card representing an organism in a Food Web and we will create a model of a Food Web.

Materials Needed:

• Science Notebook
• Pencils
• Colored Pencils or Crayons
• Blank index card (one per student).
• Yarn or string.

Next Generation Science Standards:

The NGSS standards that will be covered in this unit/ lesson are:

5-PS3-1. Use models to describe that energy in animals’ food (used for body repair, growth, motion, and to maintain body warmth) was once energy from the sun.

5-LS1-1. Support an argument that plants get the materials they need for growth chiefly from air and water.

5-LS2-1. Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment.

Disciplinary Core Ideas:  This lesson aligns to the Disciplinary Core Ideas of

PS3.D: Energy in Chemical Processes and Everyday Life  The energy released [from] food was once energy from the sun that was captured by plants in the chemical process that forms plant matter (from air and water). (5-PS3-1)

LS1.C: Organization for Matter and Energy Flow in Organisms  Food provides animals with the materials they need for body repair and growth and the energy they need to maintain body warmth and for motion. (secondary to 5-PS3-1)  Plants acquire their material for growth chiefly from air and water. (5-LS1-1)

LS2.A: Interdependent Relationships in Ecosystems  The food of almost any kind of animal can be traced back to plants. Organisms are related in food webs in which some animals eat plants for food and other animals eat the animals that eat plants. Some organisms, such as fungi and bacteria, break down dead organisms (both plants or plants parts and animals) and therefore operate as “decomposers.” Decomposition eventually restores (recycles) some materials back to the soil. Organisms can survive only in environments in which their particular needs are met. A healthy ecosystem is one in which multiple species of different types are each able to meet their needs in a relatively stable web of life. Newly introduced species can damage the balance of an ecosystem. (5-LS2-1)

LS2.B: Cycles of Matter and Energy Transfer in Ecosystems  Matter cycles between the air and soil and among plants, animals, and microbes as these organisms live and die. Organisms obtain gases, and water, from the environment, and release waste matter (gas, liquid, or solid) back into the environment. (5-LS2-1)

Crosscutting Concepts:

Systems and System Models  

• A system can be described in terms of its components and their interactions. (5-LS2- 1)

Energy and Matter  

• Matter is transported into, out of, and within systems. (5-LS1-1)  

• Energy can be transferred in various ways and between objects. (5-PS3-1)

Science & Engineering Practices:

Developing and Using Models:

Modeling in 3–5 builds on K–2 experiences and progresses to building and revising simple models and using models to represent events and design solutions.  Use models to describe phenomena. (5-PS3-1)  Develop a model to describe phenomena. (5-LS2-1)

Engaging in Argument from Evidence

Engaging in argument from evidence in 3–5 builds on K– 2 experiences and progresses to critiquing the scientific explanations or solutions proposed by peers by citing relevant evidence about the natural and designed world(s).  Support an argument with evidence, data, or a model. (5-LS1-1)

I start this lesson by asking the students what they think the difference is between a Food Web and a Food Chain. I list their responses on the board. Since we have already learned about the Food Chain, the students have more responses about this concept.

I remind the students that a food chain only shows one direction of energy flow based on one organism. For example, energy comes from the sun, to green plants, to animals that eat plants, and to animals that eat other animals. Green plants use the sun’s energy directly to make food. When animals eat green plants and other animals eat those animals, the energy moves from one living thing to another along the food chain. (Students will learn more about how the amount of energy passed along from each "trophic" level decreases in later grades but it is helpful to introduce this concept to the students). 

We also review the vocabulary Animals that eat plants are called herbivores, animals that eat both plants and animals are called omnivores, and animals that eat only other animals are called carnivores. All members of a food chain depend on the energy from the sun that green plants transform into food energy. I also remind the students that the green plants are producers and that the animals that eat the plants and other animals are the consumers.

I then show them this page: Food-Chains-Food-Web that explains the difference between the 2.

I then ask the students to compare and contrast Food Chains and Food Webs in their Science Notebooks using a Venn Diagram.

This is one of my favorite activities to explain the food web (and a classic). I have the students prepare different cards that include plants and animals from our local Mediterranean Ecosystem since we will be doing more activities with these organisms in a later lesson. I also make a card with a picture of the Sun. I have labeled each card and have handed each student a different one. 

I tell the students to draw a picture of the organism that is on the cards using photos from the Santa Monica Mountains National Recreation Area website. I will also laminate  them later to make them last a long time. These cards can also be made into necklaces by and attaching a loop of yarn and  the students can wear during the activity (and the other students can see the picture).

I tell the students that they are now going to make a food web. I take them outside (weather permitting) or to a larger indoor space on campus since they will need to make a large circle. I have distributed the organism cards ahead of time and the students are wearing these as we get in the circle. The student who is the Sun stands at the center of the circle.

I then explain to them that we will be using a ball of yarn (or string) and say that the ball of yarn represents sunbeams, or energy from the sun. I ask the student representing the sun to hold the end of the yarn tightly and toss the ball to someone who can use that energy (a green plant). When the student representing the green plant catches the ball of yarn, he or she should hold a piece of the yarn and throw the ball to someone else who could use the energy. For example, the sun might throw the yarn to the grass, the grass to the grasshopper, and the grasshopper to the meadowlark. After the yarn reaches a carnivore, I cut it off to represent one food chain. (I also explain that humans, bears, raccoons, etc. are omnivores and can end a food chain, or they could be eaten by a carnivore.) I remind the students to keep holding onto the yarn and that they might be holding more than on strand during this activity.

I then ask how can all these other plants and animals get the energy they need? (The students should respond- through a Food Chain.)

I return the yarn to the sun to start another chain. This time the sun might throw its energy to the grass, the grass to the mouse, and the mouse to a great horned owl. I cut the yarn, throw it back to the sun, and have the sun start another chain. We continue making chains until every student holds at least one strand of yarn.

I then ask the following questions (students should answer what is in parentheses) :

• Have we made food chains? (Yes, lots of them!)
• What do all of our food chains together look like? (A food web.)
• What is the difference between a food chain and food web?
• (A food web is made up of several food chains. A web is more complicated than a chain because it has connections among the chains.)
• Who is holding the most pieces of yarn? (The sun.) Why? (Because each food chain starts with the sun.)
• Who else is part of many food chains? (Green plants)
• What would happen if the green plants died? (Nothing else in the Food Web would survive).

Here are a few photos of the activity:

I then ask the students/organisms:

• How could we show what could happen if one kind of plant, such as all the grass  died? I have the student representing grass pull out his or her pieces of yarn and sit down.
• If all the grass is gone, who may have trouble getting enough food?  We identify all the animals that were in food chains that included grass. Whoever had yarn pulled out of their hands might have trouble getting enough food without the grass.
• What happened to our food web? (It is much thinner, less complex, and less strong.)
• Why should we be concerned about each kind of plant or animal? (Because other plants and animals in the food web may depend on it.)

To evaluate the activity/lesson, we go back to the classroom and I  tell the students to get out the Food Chains they created in the previous lesson and ask them to think about other organisms that can be included in a Food Web for the animal they chose. I then have them draw a food web for that organism based on our activity. 

An example of a drawing could look like this:

Here are some student Samples: