Plants have stomata and Ienticles involved in gaseous exchange. In stems the living cells are organised in thin layers inside and beneath the bark. They have openings called Ienticles. Transpiration is the evaporative loss of water by plants. It occurs mainly through stomata in leaves Food transport occurs by the vascular tissue phloem from a source to a sink. Photosynthesis is a physico-chemical process by which they use light energy to derive re synthesis of organic compounds.