Page 3 - 11-Bio-13 Gaseous Exchannge

13. Gaseous Exchange eLearn.Punjab

GASEOUS EXCHANGE IN PLANTS

Plants like animals also get their energy from respiration. In plants, in contrast to animals, no special
organ or system is present for gaseous exchange as they exist in higher animals. Every cell of plant
carries out exchange of gases according to its needs. The transport system of plants which includes
conducting tissues i.e. xylem and phloem is not involved in the transport of gases in the plants.
In most cells of mesophyll which are specialized for photosynthesis, there are present large air
spaces. These air spaces are directly involved in gaseous exchange. Stomata are the main sites of
exchange of gases in plants. Stomata are largely present in the leaves and in young stem. In older
stems, cork tissue is present which is formed of dead cells. The cork tissue has special pores called
lenticels which are involved in gaseous exchange. Land plants get their oxygen directly from air which
enters through stomata. Enormous number of stomata are. present on the leaves. It is estimated
that there are 12000 stomata per square centimeter of leaf surface in Tobacco plant. These stomata
lead to the intercellular spaces (spaces between cells) of mesophyll tissue. The air spaces are
comparable to honey comb. These
air spaces may comprise up to 40%
of the total volume of the leaf. The
exchange of gases between and the
moist surface of mesophyll cells
takes place promptly (Fig 13.1). The
roots of the land plants get their
oxygen from the air existing in the
spaces between the soil particles.
Aquatic plants obtain their oxygen
by diffusion from dissolved oxygen
in water.

Fig. 13.1 Stomata on leaf surface V: 1.1

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