Living organisms, eating representatives of the previous level, receive energy stored in its cells and tissues. A significant part of this energy (up to 90%) is spent on movement, breathing, heating the body, etc. and only 10% accumulates in its body the form of proteins (muscles), fats (adipose tissue). Thus, only 10% of the energy accumulated by the previous level is transferred to the next level. That is why food chains cannot be very long.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.