Food chains and food webs: Instructor Guide
This lesson is designed to introduce standard B-3.6: Illustrate the flow of energy through
ecosystems (including food chains, food webs, energy pyramids, number pyramids,
and biomass pyramids).
The lesson and associated activity is a different way for students to take notes without copying
from a book or overhead. The students fill in blanks on their worksheet as the teacher
lectures about the topic. At points during the lecture, the students get involved to make a
food chain and a food web from organisms found in a South Carolina salt marsh.
Materials: Ball of yarn (represents energy), index cards with name and picture of salt marsh
organisms (enough for each student), student worksheet
Part 1: Food chains
Here is one example of a food chain using salt marsh organisms:
I had students come to the front of the room and form a line. I handed the ball of yarn (energy)
to the sun and had the students pass the ball along to illustrate the flow of energy from one
organism to the other (each student holds on to the yarn as it is passed). I then drew the food
chain on the board and labeled the trophic levels, primary producers, primary consumers, etc.
Part 2: Food Webs
For this section, the ball of yarn (energy) started with the sun and was passed down through
multiple food chains to create a large, complicated web involving all the students and organisms
in the salt marsh. The students really enjoyed throwing the ball around the room from one
organism to the next and figuring out predator/prey relationships. This was also a good way to
talk about decomposition and nutrient cycling.
Once the food web was complete, I discussed what happens when humans get involved by
removing certain organisms. I made up the scenario that humans removed all of the shrimp,
crab, fish, and oysters for food and destroyed the plants for marinas and construction. Any of the
organisms that humans removed let go of the yarn. Then any organism that relied on those that
disappeared also dropped the yarn to illustrate the collapse of ecosystem.
As a class, we drew the food web on the board.
See example below of a salt marsh food web. I organized this way to make Part 3 easier to draw.
Fungi and bacteria are off to the side as decomposers and nutrient cyclers. Oyster and mussels
are also off to the side for being filter feeders.
Part 3: Ecological Pyramids
The drawing above is easily transformed into an ecological pyramid (see below).
I also included terms such as primary producers, heterotrophs, consumers, etc.