Assertion: The uptake of DNA during transformation is an active, energy requiring process.
Reason: Transformation occurs in only those bacteria, which possess the enzymatic machinery involved in the active uptake and recombination.

Both Assertion (A) and Reason(R) are correct and R is the correct explanation of A.

Transformation does not involve passive entry of DNA molecules through permeable cell walls and membranes. It does not occur "naturally" in all species of bacteria, only in those species possessing the enzymatic machinery involved in the active uptake and recombination processes. Even in these species, all cells in a given population are not capable of active uptake of DNA. Only competent cells, which possess a so called competence factor are capable of serving as recipients in transformation.