Primary consumers derive their energy by consuming producers, which are primarily plants or algae.

These primary consumers, commonly referred to as herbivores, play an essential role in the food chain. They obtain their energy from producers—organisms capable of generating their own food through photosynthesis. This remarkable process involves converting sunlight, water, and carbon dioxide into glucose, a sugar that serves as a vital energy source. Examples of producers include plants, algae, and certain types of bacteria.

When primary consumers feed on these producers, they access the energy stored in the glucose. This occurs through digestion, a process in which food is broken down into smaller molecules that can be absorbed and utilized by the body. The energy extracted from this food is then employed for various physiological functions, including growth, reproduction, and movement.

It’s important to understand that not all the energy from a producer is transferred to a primary consumer. A portion of the energy is lost as heat during digestion, while some is utilized by the producer for its own metabolic processes. Typically, only about $10\%$ of the energy from the producer is passed on to the primary consumer.

This energy transfer is a fundamental aspect of the food chain or food web. In this system, energy flows from one organism to another, beginning with the sun and culminating with apex predators. Primary consumers serve as a crucial link in this chain, connecting the energy-rich producers with other consumers within the ecosystem. Without primary consumers, the energy available to other organisms would diminish, potentially disrupting the balance of the entire ecosystem.