Question

how can you prove bark cell are impervious to gas and water

Answer 1

Take two pieces of cinnamon bark.
Place one in water and other in open air.
Leave it for two days.
We observe that the two barks placed in water and air neither swell nor shrink.
Therefore bark cells are impervious to gases and water.

Answer 2

BARK CELLS ARE MOSTLY IMPERVIOUS TO WATER AND GASES DUE TO DEPOSITION OF A MATERIAL CALLED SUBERIN. HOWEVER, THERE ARE PORES AT SOME LOCATIONS IN THE BARK CALLED LENTICELS THAT ALLOW ECHANGE OF GASES.    THERE IS NO SPECIFIC EXPERIMENT TO PROVE THIS. HOWEVER, BY STUDYING THE ANATOMY OF PLANTS, IT HAS BEEN PROVED THAT THEY ARE IMPERVIOUS TO WATER AND GASES.