Answers to Review Questions
1. Autotrophy is the use of sunlight (photosynthesis) or inorganic chemicals (chemosynthesis) to fix CO2 and synthesize energy storage compounds containing carbon-carbon bonds.
Photosynthesis occurs in archaea, bacteria, protists, algae, and plants. Heterotrophy is the consumption of organic matter to obtain energy. The organic matter includes both living and dead organisms. Living organisms vary in their mobility, and their consumers (predators) have adapted ways to improve their efficiency in capturing their food (prey). Dead organic matter can be eaten and digested internally by multicellular heterotrophs or externally broken down by enzymes excreted into the environment and then absorbed by archaea, bacteria, and fungi.2. CAM plants open their stomates to take up CO2 at night, when the humidity of the air is higher than it is during the day. They store CO2 in the form of a four-carbon organic acid, then release it to the Calvin cycle during the day. The storage of CO2 allows the stomates to be closed during the day, when the potential for transpirational water loss is greater.
3. Live animals are a higher-quality food source, but they are rarer and thus harder to find, and they may have defense mechanisms that require expenditure of energy to overcome. Plant detritus is abundant in many ecosystems, so little energy needs to be expended in locating it, but its food quality is low.