6. How do scientists account for the decrease in available energy from one trophic level to the next higher trophic level?
A. The energy is available to organisms at lower trophic levels.
B. The energy of the sun cannot be fully exploited by producers.
C. The energy is stored in energy-dense molecules for decomposers.
D. The energy is used by organisms for life functions or is lost as heat.

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area