Flow of energy through living organisms

[Misr]

Hi there ,


[quote name = "An extract from my book"]

The pyramid of mass
Represents the relation between the masses of living organisms if food chain

Disadvantages :
It does not take in to consideration amount of food during a long period of time.



so my problem is that line :

"Disadvantages :
It does not take in to consideration amount of food during a long period of time."

Can u rephrase this in a better way and explain it to me??

Also



The pyramid of energy:
has no disadvantages as it considers the rate of food production and its total weight.


so , why??

Thanks very much