According to research it is specified that ground tissues transport water and nutrients from roots to the upper parts of plants. Further it also store surplus sugar and also provide physical support to plant to make it firm and stand.
But ground tissues does not produce Sugar.
Reference: Paquette, Alice J., and Philip N. Benfey. "Maturation of the ground tissue of the root is regulated by gibberellin and SCARECROW and requires SHORT-ROOT." Plant physiology 138.2 (2005): 636-640.
Ten Percent Rule: What happens to the other 90% of energy not stored in the consumer's body? Most of the energy that isn't stored is lost as heat or is used up by the body as it processes the organism that was eaten