Of the thorns or spines and the greeny pigmented hard part of the cactus are the leaves and why?​

The spines of a cactus are exactly not the leaves, but they are the solid hard part that reduces the rate of transpiration, so as to level the water constant in the cactus' body. They are important as it can reduce the animals from eating the cactus.

However, camels have thick jaws and can eat cactus easily .

Hope it helps you...

(Answered by Benjemin)

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.