Relative to prokaryotic organisms, eukaryotes are fairly limited in the ways they obtain carbon and energy. Moreover, the metabolic processes that power eukaryotic cells take place only in specific organelles—aerobic respiration in the mitochondrion (Chapter 7) and photosynthesis in the chloroplast (Chapter 8). Only limited anaerobic processing of food molecules takes place within the cytoplasm.

As noted above, many eukaryotic cells engulf food particles and package them inside a vesicle, which is then transported into the cytoplasm. Within the cytoplasm, enzymes break down the particles into molecules that can be processed by the mitochondria. Many single-celled eukaryotes feed on bacteria or other eukaryotic cells, and animals, in turn, ingest larger foodstuffs, including other animals and plants. In consequence, eukaryotes can exploit sources of food not readily available to bacterial heterotrophs, which feed on individual molecules. This ability opens up a great new ecological possibility—predation—increasing the complexity of interactions among organisms.

The structural flexibility of eukaryotic cells also allows photosynthetic eukaryotes to interact with their environment in ways that photosynthetic bacteria cannot. Unicellular algae (which are eukaryotes) can move effectively through surface waters vertically as well as horizontally and therefore can seek and exploit local patches of nutrients. Diatoms, discussed shortly, go one step further. Large internal vacuoles allow them to store nutrients for later use when nutrient levels in the environment may become low. Plants have evolved multicellular bodies with many different cell types, allowing them to capture sunlight many meters above the ground. That ability gives plants a tremendous advantage on land, as long as their leaves can obtain water and nutrients from the soil in which the plants are rooted.