What organism is likely to be in the bottom trophic level of a food chain?

Single Celled of some kind depending on the environment.

To determine the organism likely to be in the bottom trophic level of a food chain, it's helpful to understand the concept of trophic levels. Trophic levels represent the positions that organisms occupy in a food chain based on their feeding relationships.

The bottom trophic level, also known as the primary producer level, consists of organisms that produce their own food through photosynthesis or chemosynthesis. These organisms are called autotrophs. They convert energy from the sun or inorganic compounds into organic molecules that can be utilized by other organisms.

In most ecosystems, the primary producers at the bottom trophic level are typically plants or algae. They use sunlight, water, and carbon dioxide to synthesize organic compounds (such as glucose) through the process of photosynthesis. These primary producers form the foundation of the food chain as they provide energy and nutrients for other organisms.

However, in certain environments like deep-sea hydrothermal vents or arctic tundra, where sunlight is limited, primary producers can be non-photosynthetic organisms. In these cases, chemosynthetic bacteria or archaea use chemicals from their surroundings to create organic matter, thereby occupying the bottom trophic level.

Therefore, the specific organism at the bottom trophic level can vary depending on the ecosystem. It can be plants, algae, or even chemosynthetic bacteria/archaea, depending on the availability of resources and the environment in question.