In an ecosystem, the least efficient energy transfer link is from the

Analyze the question: It asks which link in an ecosystem's energy flow transfers energy with the lowest efficiency, meaning the smallest percentage of energy is passed on.

Concept: Energy enters an ecosystem as sunlight. Plants (producers) capture only a very small fraction of it through photosynthesis. After that, each trophic transfer follows the "10% rule" (roughly 10% of energy passes to the next level).

Step-by-step comparison:

• Sun to producers (B): Only about 1% or less of the solar energy reaching the Earth is converted to chemical energy by photosynthesis. Much of the light is reflected, absorbed as heat, transmitted, or falls on non-photosynthetic surfaces, and it is also limited by the wavelengths chloroplasts can use.
• Producers to primary consumers (D): About 10% is transferred.
• Primary to secondary consumers (C): About 10% is transferred (sometimes up to 10-20%).
• Secondary consumers to decomposers (A): Decomposers receive energy from dead remains and waste at all levels. This is not a typical low-efficiency feeding step.

Comparing the figures, about 1% (sun to producers) is lower than about 10% for the consumer links. So the least efficient link is the first one.

Tip: Remember "1% in, 10% along." Only about 1% of sunlight is captured by producers, then roughly 10% passes at each later trophic level. When a question asks about the "least efficient" step, think of the sun-to-producer link first.