Final answer:
The statement regarding phytoplankton as photosynthetic microorganisms that are vital to larger marine organisms like whales is true. They are key producers in water ecosystems and importantly impact global energy flow and oxygen levels.
Step-by-step explanation:
The statement that phytoplankton are microscopic organisms performing photosynthesis and serving as a significant food source for larger organisms such as whales is true. Phytoplankton are classified among the producers in the aquatic ecosystems and are essential for the oceanic food webs. As part of the plankton group, they are primarily categorized as either bacteria or algae. They live in the photic zone of bodies of water, where sunlight penetrates, allowing them to carry out photosynthesis. Energetically, they are crucial, capturing approximately half of the energy that flows through the Earth's biosphere. Furthermore, their abundance and health influence the availability of oxygen within aquatic environments, especially since they need to remain suspended in the upper water columns to access light effectively. Lastly, phytoplankton diversity can be influenced by environmental factors, like temperature and nutrient availability, which in turn affect larger marine ecosystems.