Transfer cells, a type of companion cell, differ from Ordinary companion cells in such a way that they have:
Dense cytoplasm
Few or no plasmodesmata
Much folded walls
Abundant mitochondria
There are three types of companion cells: ordinary companion cells, transfer cells and intermediary cells. All three cells have dense cytoplasm and abundant mitochondria. Ordinary companion cells have smooth walls and few or no plasmodesmata connections to cells other than the sieve tube. Transfer cells are like ordinary companion cells, but have many folded walls that are adjacent to non-sieve cells, allowing for larger areas of transfer. Hence, the correct answer is option 3.