dear student,
The transfer of energy in an ecosystem across the food chain is always unidirectional because once the solar energy is converted into the chemical energy by the producers, it cannot be reverted to the sun and the consumers are not capable of fixing the solar energy into the chemical forms. So, at each trophic level, energy is lost as respiratory losses which reduces the amount of energy available to the next trophic level. It cannot be given back to the previous trohic level. This makes the pyramid energy to appear upright.
Hence, the correct answer is 'Always upright'
regards,
team Askiitians
