This is a thought puzzle. Place the following items on a sheet of paper so that they show levels of interaction. Which is the most important item? Which items are dependent on others? Here are the pieces:

• People are starving.
• Commercial fertilizer production requires temperatures of 900°C.
• Geneticists have developed plants that grow very rapidly and require high amounts of nitrogen to germinate during the normal growing season.
• Fossil fuels are stored organic matter.
• The rate of the nitrogen cycle depends on the activity of bacteria.
• The Sun is expected to last for several million years.
• Crop rotation is becoming a thing of the past.
• The clearing of forests for agriculture changes the weather in the area.

Why do some farmers use legumes in a rotation of crops? How are legumes related to bacteria and the nitrogen cycle? What happens if farmers do not use legumes in a rotation of crops? If new varieties of crops require more nitrogen where will the nitrogen come from? What is the source of the energy used to produce the high temperatures needed to produce fertilizer? How is the sun related to fossil fuels? How is food production related to starvation?