Which organisms form the base of the food web by converting inorganic carbon into organic matter?

• A. Primary Producer
• B. Primary Productivity
• C. Nutrient
• D. Oceanic Zone

Answer: (A)

Primary producers form the base of the food web because they take inorganic carbon, like CO2 or bicarbonate, and convert it into organic matter through photosynthesis (and, in some environments, chemosynthesis). In oceans, phytoplankton are the main examples: they use sunlight to drive carbon fixation, turning CO2 into sugars that become the food for everything higher up the chain. This step is essential—the energy and organic material entering the ecosystem come from these autotrophs, so the rest of the organisms depend on them for nourishment.

The other options refer to a rate of production (how fast organic material is made), a substance that organisms need (nutrients), or a region (an oceanic zone), none of which describe the organisms themselves that fix carbon.