An ecosystem includes all of the living and non-living factors interacting in an area. A food web represents the feeding relationships between all of the organisms in the ecosystem. While it is not an organism, the sun is often included in food webs because it supplies energy for almost all producers on earth, with the exception of those found in a few deep sea ecosystems. In the sample food web included below, the green bubbles represent producers which are organisms who produce their own food through photosynthesis. The orange bubbles represent the primary consumers that eat producers. The red bubble represents a secondary consumer that gets energy by eating primary consumers. The purple bubble represents a tertiary consumer that gets energy by eating primary and secondary consumers. Tertiary consumers are also often the top predators in an ecosystem meaning that they do not have any predators. The turquoise bubble represents decomposers who get energy by breaking down dead matter and recycling nutrients back into the environment. To be technically correct, there should be an arrow from each organism to the decomposers because all organisms are broken down and recycled once they die. However, for ease of viewing the food web, just a few arrows from different trophic levels are included here.
(For more information about food webs and trophic levels see: http://www.seagrant.sunysb.edu/ifishny/pdfs/lessons/inclass/middleschool/FoodWebs-background.pdf)
The engineering design process will help students as they are creating their mobiles. There are many different, but essentially similar versions of the process. For one version and some background information see: http://www.nasa.gov/audience/foreducators/plantgrowth/reference/Eng_Design_5-12.html
The version that I like to use with my students is from PBS kids:
Basically, the students should be comfortable brainstorming ways to tackle a task or solve a problem. Then, they need to be able to design and build based on their ideas and to try out their design to see if it solves the initial problem. If not, students should be able to develop alternative solutions or ways to improve their design. Then, they need to be comfortable revising and redesigning to improve upon their solution. Once they have developed and built the best solution possible, they should be able to communicate their final result and the process used to get to it to others.
The type of mobile that each group creates will depend a lot upon the skill and experience level of the students in that group. For struggling students or those with basic hands-on skill levels, a simple coat hanger design (described in the procedure below) works well and allows the students to at least demonstrate their science knowledge. However, this design might be too easy for more accomplished or artistic students. If you think your students will feel comfortable making a more advanced mobile using wire such as the mobile pictured here, the website below provides some guidance.
Since this activity is quite open-ended, it is excellent for a differentiated classroom. Students with higher abilities can be free to develop and create their own designs, while you can guide struggling students more closely.