Q.The small pores present on woody stem surface with bark and which carry out gaseous exchange are ______.

Gaseous Exchange in Plants

Unlike animals, plants do not have specialised respiratory organs or a system to transport gases over long distances. Gaseous exchange in plants is comparatively simple, for several reasons:

• Each plant part (root, stem, leaf) largely takes care of its own gas-exchange needs; there is little transport of gases from one part to another.
• Most cells of a plant have at least a part of their surface in contact with air — through stomata (leaves and green stems), lenticels (woody stems), and the general surface of roots — because of loose packing of parenchyma cells with large intercellular air spaces.
• The rate of respiration in plants is much lower than in animals, so their oxygen demand is modest and can be met by simple diffusion.
• Being non-motile and having a high surface-area-to-volume design, diffusion over short distances suffices.

Therefore oxygen diffuses in and carbon dioxide diffuses out directly across these surfaces without any breathing mechanism, blood or respiratory pigment. Living cells of bark are supplied through lenticels. …