Food Chain or Food Web?

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SWBAT distinguish between a food chain and food web.

Big Idea

This lesson guides students through the intricacies of distinguishing between a food chain and a food web. As well as, learning the importance of both in the ecosystem.

Setting the Stage

5 minutes

This lesson is a precursor to the Over Fishing our Oceans lesson.  It builds background knowledge and adds more understanding of the lesson.  In the next lesson it will become important for the students to understand that fish in the ocean do not eat all other fish and that some only sustain on plankton (seaweed).  Without this understanding, the next lesson will seem a bit confusing.  

Food chains and food webs are not clearly or directly connected to any standard within the NGSS, however, in the Framework for K-12 Science Education, LS1.C  focuses on Organization for Matter and Energy Flow in Organisms.  It explains that grade band K-2 should focus on the need all animals have for food in order to live and grow.  It also defines that by the end of Grade two, all students should understand this.  

Thus the need to explore and explain the food chain and food webs. 


10 minutes

While the children are at their tables, I bring each team a set of pictures.  (Slide one of the Food Chain pictures cards).  I explain that I am not going to tell them how to sort or organize the pictures. I am curious to see what they will do with the pictures. The children are comfortable with my directions and beginning sorting.  

I allow them to puzzle the situation out and struggle.  I do not offer any suggestions. I simply allow them to work through the cards.  When I see that they are not able to make any order with the pictures, I invite them to the rug with me.

I show them the book Dory's Story and I begin reading. I allow the language to sink in.  I read it slowly and emphasis the connections each time a new one is introduced in the story.  

The language of the writing is beautiful and simple at the same time.  I continue to read and finish the entire book.  When I have finished reading the book, I ask the children if they notice anything special that happens in the story?  

Many of the children will pick up on the connection between the pictures they were working with and animals in the story.  

A few students will have background knowledge and bring up the language of a food chain.  I ask them to hold on to that thought.  When students have prior knowledge about a subject, I acknowledge their knowledge, but I also want to hold on to sharing it before the complete lesson can be taught.  More so with science.  Students may have misconceptions that I want to be cautious about sharing and having to correct later for other students.  When the lesson addresses a major concept like this (one that will be used in many lessons later in their learning), I want to make sure that all the students have an even and clear understanding of the learning.  I do not want to cloud the learning with too many ideas. Especially, an idea or misunderstanding that is not correct.  

If a student does share the knowledge of a food chain, I ask the child to hold on to that information.  I explain to them how powerful it can be to know something before others do.  I ask that they wait until we have completed the lesson and then we will check what they know.  



10 minutes

I send the children back to their tables and explain that I want them to sort the cards a second time. This time, they have no struggles organizing the pictures.  They do it quickly and can even explain their rationale behind their thinking. 

After the students have worked through the first set of pictures, I give them a second set of cards (Slide two of picture cards).  I explain that because they were able to sort the first set out, I would like them to sort this set out.  However, I will not offer any suggestions, I want them to work on their own within their teams.  The second set of cards are not a food chain, but a food web.  This will prove to be much more difficult because there is no easy way to organize them to depict the connections the animals have to one another. I anticipate this will cause the children some uncomfortable feelings because it will not be easy or obvious. 

I allow the children to work through the cards until I see them become stumped. I don't want to let them get to the point of frustration, just to the point they are not sure what to do.  It is a fine line.  If they become frustrated, they will not want to continue.  


10 minutes

When I feel the children are at the point that they need to have an explanation, I get their attention and direct them to look at the screen.  The Food Chains or Food Webs power point is ready to go and Slide one is on.  

Instantly, the children make their connections.  Especially, any of those children who have prior knowledge that I asked to hold on to their knowledge.  

I begin with Slide two and show the children the blank slide.  I have the pictures sequenced so they come in on a click.  The first picture to arise, is the phytoplankton, followed by the shrimp and the rest of the animals.  The food chain on the screen follows the food chain that is used in the book we read (Dory's Story).  At this point, I have not really explained to the children what phytoplankton is.  I am waiting to dig deeper into this description until we have mastered the understanding of the food chain and food webs.  

While I am working through the slide and the order of the animals in the food chain, I notice some children reorganizing their pictures to match what they see on the screen. 

I move to Slide three and read the definition of a food chain.

I move to Slide four and the animals are on the screen.  I have timed the arrows to only come on the screen on my click.  I did this so I could talk through the connections to the children.  It begins with the purple arrows.  The children will instantly see the connection to the Whale lesson

After the purple, comes the blue, red, green and then yellow.  Using the arrows makes it more visual and less confusing to see which animals eat the other animals.  

Slide five. Then shows a box with just the arrows inside.  I put this in to show web like connections. My expectations will be that the children will notice that the web is much more complicated than a simple food chain.  


10 minutes

When we have finished discovering the differences between the food chain and the food web, I read another book to the children; The Sea That Feeds Us.  It is another fantastic book about food chains and webs, but does a marvelous job of explaining the phytoplankton and it's essential role in the ecosystems.  

I read this book after the previous work has been taught to hold the emphasis on the phytoplankton. Without it, the rest of the animals would not be able to sustain.  If this concept is taught early on, it may not have the impact in learning that I want it to have.  



10 minutes

To see what the children understood from the lesson, I ask them to open their journals and use their pictures to draw and sketch out a model of a food chain.  I allowed them time to complete their sketches.  While they were busy working, I circulate throughout the classroom observing the models in action.  

When the children begin to finish up, I tell them to prepare for the food web.  They have the pictures in front of them and they are able to begin to put them in an organization that makes sense.  I put up the screen that has the arrows, but no animals on it.  

I do this because while I am sure they can connect the animals, I know that it could be challenging to remember the arrows and how to draw them.  I explain to the children that they are able to do document their model in any way that makes sense to them.