Energy flow in ecosystems
The only source of energy for life on Earth is the Sun. Producers (autotrophs) turn solar energy into chemical energy in photosynthesis and make organic matter. Herbivores that eat plants are first-order consumers; predators that eat them are second-order consumers; animals that eat those are third-order consumers. When plants and animals die, reducers break them down. A food chain is a sequence of organisms in which each is food for the next; each link is a trophic level. For example: plant → grasshopper → frog → stork. From one link to the next only about 10 percent of matter and energy passes on; the other 90 percent is used for the organism’s life processes (movement, heat, growth). So each next level is about 10 times smaller than the previous, and stacking the trophic levels gives an ecological pyramid: the most producers at the bottom and the fewest predators at the top. A chain is rarely longer than 4–5 links.
Game “The 10 percent rule”: give the producers 100 beans (or paper bits). The “herbivores” may take only 10 of them, the “predators” take 1 from the herbivores. Record the results in a table and draw a pyramid. Extra: make a food chain from cards (plant → grasshopper → frog → stork) and name each link “producer”, “first-order consumer”, “second-order” and so on. Safety: do not use edible items for the game; keep small beans out of mouths.