Final answer:
In deep areas of the ocean devoid of sunlight, plants and other organisms utilize chemosynthesis, a process that relies on chemical energy to produce food, to sustain their energy needs.
Step-by-step explanation:
Plants that live in very deep areas of the ocean, where sunlight cannot reach, use a process called chemosynthesis instead of photosynthesis for their energy needs. In the absence of sunlight, these organisms rely on the oxidation of inorganic molecules, such as hydrogen sulphide or methane, to produce organic compounds. A prime example of this process occurs around deep-sea hydrothermal vents where chemoautotrophic bacteria use chemical compounds flowing from Earth's interior to synthesize food. These bacteria are then the foundation of a unique ecosystem, providing energy to a variety of organisms like giant tubeworms and other deep-sea creatures.