What primarily limits the length of a food chain?

• A. The color of primary producers
• B. The inefficiency of energy transfer along the chain
• C. The number of predator species
• D. The amount of sunlight

Answer: (B)

Energy transfer between trophic levels is inefficient, so only a portion of the energy stored by producers makes it to higher levels. Much of the energy is lost as heat through metabolism, movement, and waste, so the amount available declines at each step. This cumulative loss creates an energy bottleneck, meaning there isn’t enough energy to support many successive levels. As a result, food chains tend to be short—typically only three to five trophic steps—because the energy needed to sustain higher predators drops too quickly.

The other options don’t set this limit in the same way. Sunlight supplies the initial energy for the entire system but doesn’t by itself determine how many levels can be supported. The color of producers and the number of predator species don’t dictate the maximum number of steps in a chain; they’re not the primary factor shaping chain length.