What is a hydrogen bond and why is it not a true bond

Hydrogen bond: It is a type of bond which exist between hydrogen atom and other atom having high value of electronegativity. Those atoms having high electronegativity values has the capability to attract the shared pair of electron towards itself. Hydrogen atom have very low value of electronegativity, so the shared pair of electron goes farther from it and nearer to high electronegative atom such as oxygen in water molecule. This bond is very weak than covalent bond.

It is not true bond due to weak force of attraction between atoms.

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.