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Ecosystems and Their Interconnectivity

1. A habitat only refers to where it lives. A niche, however, also takes into consideration its role in the environment: what it eats, how it reproduces, if it is prey for other organisms, when it sleeps, and so on.

2. The graph depicts the competitive exclusion principle. Both species are initially growing well, but at day 4, resources become limiting and species A outcompetes species B. Species B eventually dies off, leaving only species A to occupy this particular niche.

3. Each step in a food chain depicts the transference of energy as one organism eats another. The second law of thermodynamics states that every time energy is converted from one form to another (such as an herbivore eating plants and then transforming the energy of the plants’ tissues into ATP), the process is not 100% efficient. In fact, only a measly 10% of the plants’ stored energy is able to be used by the herbivore. That means that, eventually, the available energy will become too small to support another step in the food chain (another trophic level).

4. Photosynthesis is the only process through which carbon dioxide is removed from the atmosphere. Once it is locked into tissues (thanks to food chains), carbon dioxide is released back into the atmosphere through cellular respiration and decomposition. Burning of fossil fuels also releases a massive amount of carbon dioxide.

5. The competitive exclusion principle states that two different species cannot occupy the same ecological niche. The survivor is the one who was able to outcompete the other.

6. The first trophic level must be a producer (autotroph) because every chain is built upon the energy provided by the sun. The only type of organism able to harness photons of sunlight are autotrophs, either photosynthetic plants, protists, or bacteria.

7. Earth is a closed system in regards to matter, but an open system in regards to energy.

8. The first step of the nitrogen cycle is nitrogen fixation, when nitrogen gas is fixed into organic molecules. The two means of nitrogen fixation are lightning and nitrogen-fixing bacteria.

9. a. Denitrifying bacteria remove nitrogenous compounds from the soil. If the numbers of denitrifying bacteria in the soil decrease, the amount of nitrogen that remains in the soil would increase.