Quiz Key – each question worth 2 points

1. This is partially correct because of ecological efficiency. If humans eat vegetables instead of meat, there are fewer steps in the process of energy transfer from the sun to humans. However, it is only correct if the land on which cows are grazing could have been used to grow vegetables eaten by humans. If they are grazing on land that can only sustain grass, etc., then in this case meat increases the food supply because that is the only way that land can be used to produce human-edible food, provided it is grazed sustainably.

2. Entropy states that energy is lost with each transfer, moving from order to disorder. Since only 10% of the energy is transferred at each trophic level, very little of the original energy from the sun actually makes it to the highest trophic levels. Thus, there aren’t enough herbivores to support many carnivores due to low ecological efficiency.

3. Decomposers break down dead organic matter and release the nutrients in forms usable by other organisms. In addition, they decompose organisms such as tidal grass (i.e., Spartina), which cannot easily be eaten by other herbivores. Thus, the energy in the Spartina becomes available to other organisms mainly because they can eat dead plants which are rich with microbial decomposers. Decomposers are also responsible for many human foods, such as cheese, wine, etc.

4. Nitrogen fixation is the conversion of free nitrogen (N2) in the atmosphere to ammonia or nitrates by certain strains of bacteria. Since nitrogen is essential to life and is unusable to most organisms as free oxygen, fixation is necessary to make it available for use by the vast majority of organisms on the planet.

5. Humans tend to disrupt the flow of biogeochemical cycles. Humans don’t change the stocks, they alter the rate of flow between stocks. There are many examples.