OBJECTIVE: to look at the flow of energy through food-chains and food-webs.
TIME: 30 - 45 minutes
YOU WILL NEED: book illustrating marine plankton; ball of yellow wool. Plants, animals and their physical surroundings should not be studied in isolation from each other.
There is no need to get hooked up on naming things. Instead, look for examples of how things are interacting and depending on each other when you are out there on the reserve.
Before the Activity
Introduce the terms: producer and consumer; primary and secondary; and herbivore, carnivore, omnivore, detritivore and decomposer.
The best time to introduce the idea of food-chains or webs is just after the group have eaten something so that they can relate to what has just been eaten.
All food-chains start with the sun. Ask the question: "Give me the name of a food you've just eaten which doesn't originate from the sun's energy?"
Ask the children to make a chain to work out where their food originated from.
For example: milk... cow - grass - sun
crisps... potatoes - sun
sausages... pork or beef - pig or cow - plants - sun
The sun is the source of energy for all living things.
(It has now been discovered that some deep ocean communities are powered by sulphide gases, but all terrestrial food-chains are powered by the sun.)
The simplest way of looking at interrelationships between plants and animals is to look at a food-chain showing the feeding relationships, and the flow of energy between plants and animals from the sun.
All life is interdependent, and ultimately dependent on the sun. Many larger animals eat more than one thing, so they fit into several food-chains. These food-chains link together to form a food-web.
A simple seashore food-chain
Take a walk on the beach. Use it as a final activity after watching the birds or seals on the shore or looking at the life in the sand.
Talk about the plants and animals in the sea that you can't see - plankton (have some pictures to show them). Animal and plant plankton are microscopic wildlife floating in the sea, in millions, providing food for many sea-living creatures i.e. from barnacles to whales.
Look at the shells on the beach - these are all empty, but once held animals within them. What did they feed on? What fed on them?
When you have discovered enough creatures (alive and dead!) to form a food-chain, divide the children into small groups. In their small groups they each chose what they will be (not forgetting the sun) and link arms or hold hands in the relevant order; forming a food chain.
Ask everyone to spread out into a large circle. Take a ball of yellow wool or string (explain that it represents the sun's energy) and ask a volunteer to be the sun.
Ask: what are the smallest plants in the sea catching the sun's energy? (plant plankton); and the largest plants in the sea (seaweed). Connect both of these to the sun with wool.
What eats plant plankton? (animal plankton, whale, barnacle) Connect these into the web and continue in a similar fashion for seaweed. Continue through the food-web until everyone is linked up.
Remember to ask what happens to the plants and animals when they die. What are the advantages of being a scavenger?
When everyone is linked up, you can demonstrate some of the problems human activity has brought to natural food-webs - anything affected has to lie down or pull the strings it holds, anything that feels the string being pulled also lies down and so on.
Look at, and discuss, the effect of: oil pollution affecting plankton; over-fishing small fish; disease affecting mussels, or salmon.
- Recreate the food-chain or web as a wall display, or a 3D representation. Provide everyone with an A4 sheet to write down the food-chain or web for themselves.
- Carry out more research on the animals and plants, finding illustrations or information to add to the display.
- Most food-chains have only 3 or4 links, although some may be longer. Set it as a challenge to find the longest.
- Go and visit a local woodland, or investigate the wildlife of the school grounds. Try making up a woodland or school grounds food-chain or web from your own experiences or from research.
Compare the two different environments.