Answer:
It is lost most often as heat.
Step-by-step explanation:
For example, grass photosynthesis, converting light energy from the sun to chemical energy for it to use. To begin with the grass is unable to make use of all the light energy available, only what it can absorb. Now when this grass is eaten by a cow for example, if the grass absorbed x amount of energy from the sun, the cow is likely to only be able to take a tenth of x. At any trophic level, only around 10% can be passed to the next level. The other 90% is generally lost as heat from respiration, movement and other metabolic processes.
Hope this helps!