Explanation
The correct answer is (A) Phytoplankton.
Phytoplankton serves as the primary source of food for marine life. These microscopic, plant-like organisms are found in large quantities in oceans, seas, and other bodies of water. Phytoplankton undergo photosynthesis, utilizing sunlight, water, and nutrients to produce organic matter and oxygen. Their productivity forms the basis of the marine food chain.
Zooplankton (option B) refers to small, drifting animals that consume phytoplankton and are themselves an important part of the marine food web.
Seaweed (option C) is a type of macroalgae that provides habitat and food for some marine organisms but is not the primary source of food for marine life.
Grass (option D) is a terrestrial plant and is not a primary food source for marine organisms.
