Why is less energy available at higher trophic levels?

Think of a trophic level as a group of organisms in a feeding position, and of biomass as the living material that can be eaten. Energy reaches an organism in food, but not all of that energy becomes new biomass. Organisms use energy for functions such as respiration, and some is released as metabolic heat. Also, some food is never ingested or assimilated, so energy leaves as waste. That leaves less energy stored in biomass to support the next level. [S1]

A simple diagram is:

Food energy at one level
        |
        +--> used for organism functions; some released as heat
        +--> not ingested or assimilated; leaves as waste
        |
        +--> remaining energy stored as biomass
                    |
                    +--> available to the next trophic level

The arrows show pathways, not amounts. Energy that is used or leaves as waste is not necessarily passed on as biomass to the next level.

Yes. Read the vertical sequence as feeding levels and the side arrows as energy that does not become biomass available to the next level:

                 less energy available
                         ↑
Secondary consumers  -- energy in biomass --> next level
        ↑                          |
Primary consumers    -- energy in biomass --> next level
        ↑                          |
Producers             -- energy in biomass --> next level
                                      |
                 At each level: energy used for functions,
                 some released as heat; some food not
                 ingested or assimilated leaves as waste

This is a qualitative diagram: it shows the pattern and pathways, not a measured scale. The horizontal arrows mean that biomass at one level can support organisms at the next level; they do not mean all the energy at that level is passed along. In a clearer drawing, you can make each upward arrow narrower to suggest that less energy is available, but label the widths “illustrative,” not measured.

Use the data the worksheet gives, and say whether your drawing is conceptual or based on measurements. If no data are given, draw a qualitative pyramid with a broad producer base and progressively narrower levels above it. Add a note such as “width represents relative energy available; no numerical scale shown.”

If a percentage is supplied, identify it as an example tied to its ecosystem. For instance, OpenStax describes a Silver Springs example with about 14.8% transfer efficiency between its first two trophic levels, but that figure is not a universal percentage. The source also notes that estimates and measurement vary with the ecosystem and available observations. [S1] That example alone does not establish a transfer percentage for a different ecosystem, or for every step in a food chain.

Copy and adapt this:

Less energy is available at each higher trophic level because not all food energy becomes biomass. Organisms use energy for their functions, some is released as metabolic heat, and some food is not ingested or assimilated and leaves as waste. The remaining biomass can support the next level. The amount transferred varies, so this diagram is qualitative rather than a universal percentage.

For a measured pyramid, replace “qualitative” with a description of the data and its source. Keep the levels and units consistent with the assignment. The source explains why energy available as biomass decreases, but it does not supply a universal percentage for every ecosystem. [S1]