Fuel Garden: Matter and Energy from the Team's Garden to the Track

Grow It, Run On It, Feed It Back

1Yaretzi Moreno runs the 1,600 m for the Cedar Hill Middle School track team. Her coach, Mr. Bjorn Adeyemi, likes to tell the team that training is only half the work, and the other half is fuel. Two years ago, the team started a garden behind the bleachers. They grow beans, kale and sweet potatoes for the team's Friday pasta dinners, and the leftover stems, peels and plate scraps go into a worm bin. The bin's castings, the dark, crumbly waste the worms leave behind, are mixed back into the garden soil.

2Yaretzi's science teacher, Ms. Hollis Nwachukwu, challenged her to model how matter and energy move through this small ecosystem. In the model, the bean plants are producers, the runners are consumers, and the worms and the microorganisms in the bin are decomposers.

3Yaretzi's model has seven arrows. Arrow 1: light from the Sun reaches the bean leaves. Arrow 2: carbon dioxide moves from the air into the bean leaves. Arrow 3: beans move from the plants to the runners as food. Arrow 4: the runners give off carbon dioxide to the air and heat from their bodies. Arrow 5: leftover stems and scraps move into the worm bin. Arrow 6: castings move from the bin into the soil. Arrow 7: water and nutrients such as nitrogen move from the soil into the bean roots.

4To test parts of her model, Yaretzi ran two investigations. First, she set up three closed plastic bins with the same damp shredded-paper bedding at room temperature: one with 1 kg of scraps and 500 g of worms, one with 1 kg of scraps and no worms, and one with bedding only. She measured the carbon dioxide in each closed bin and, after four weeks, weighed the scraps that were left (Table 1). Second, she planted the same bean seeds in two 2 m² garden beds that got the same sun and water, and mixed castings into only one of them (Table 2).

5Finally, Coach Adeyemi asked the team whether it matters for energy if a runner eats beans or chicken. Ms. Nwachukwu gave them a model food path in which each crop stores 10,000 kJ of energy in the parts that are eaten (Table 3 in Section 3).