What it shows
In a paddy field many food chains join into a web. A hanging mobile with threads showing who eats whom makes it easy to see how energy passes from rice plants to the top animals.
The science
Producers, such as rice and algae, make food by photosynthesis using sunlight. Herbivores such as grasshoppers and caterpillars eat producers, and carnivores such as frogs, snakes, egrets and eagles eat other animals. Energy moves up the chain, but most is lost as heat at each step, which is why there are fewer top predators than plants. Decomposers like fungi and bacteria break down dead plants and animals and return minerals to the soil.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A bamboo hoop, an embroidery ring or a cut-out cardboard circle
- Card cut-outs of: rice plant, algae, grasshopper, caterpillar, fish, frog, water snake, egret, eagle, fungus and a bacteria cluster
- Coloured threads in two colours
- A paper punch or a pin
- Glue and markers
- Colour labels
Safety
For this project: An adult must use scissors and the pin or punch. Keep thread out of reach of very small children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Draw and colour each organism on card, 8 cm tall, and write its name on the back.
Group them into producers, herbivores, carnivores and decomposers and decide which animals eat which.
Hang the producers along the bottom of the hoop and the top predators from the top row with the other animals between.
Use one colour of thread to join each plant or animal to the one that eats it, and make the thread pass over the hoop to show direction.
Use a second colour to connect dead things and the decomposers at the bottom.
Hang the finished mobile from the ceiling and label the arrows with "eaten by".
Find and write down at least four different food chains, such as rice, grasshopper, frog, snake and eagle.
Remove one animal card, such as the frog, and discuss what would happen to the animals above and below it.
What you should see
A hanging web shows linked food chains in a paddy field, and removing one organism shows which others are affected.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What are producers?
Green plants and algae that make food using sunlight.
2What do decomposers do?
They break down dead matter and return minerals to the soil.
3Why are there fewer eagles than grasshoppers?
Energy is lost at each step of the chain, so less is left for the top.
4What happens to grasshoppers if frogs disappear?
Their numbers may rise, which could damage the rice.
Take it further
Draw a second food web for a pond or a forest near you and compare the producers and top predators.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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