Saturday, 7 February 2015

GASEOUS EXCHANGE IN PLANTS

Pants get their energy from respiration. The respiration is, therefore, also important for life of plants. Plants have no special organ or system for exchange of gases. The gaseous exchange is plants occur in cells of every part of the plant i.e. roots, stems and leaves etc according to their energy demands. The conducting system (xylem and phloem) of plants for water and nutrients is not involved in the diffusion of gases to the plants. The air spaces presents between the cells of parenchyma of leaves, stem and roots are involved in the gaseous exchange. In the leave and young stems, gaseous exchange occur through stomata and some exchange of gases also occur through cuticle.

         In woody stem and roots there are dead cells beneath the epidermis which form cork tissue. This tissue has pored called lenticels which are involved in gaseous exchange . the aquatic parts obtain oxygen for their respiration by diffusion from the dissolved oxygen in water. Whereas the land plants get their oxygen from air directly through their stomata which are more abundant on the lower surface than the upper surface of leaves. The roots get their oxygen for gaseous exchange through diffusion from the air existing in the space between soil particles.

Process of respiration:
      The respiration in plants continues day and night. In this process, the oxygen from the airspaces in the leaves and stems diffuses into tissues and cells of the plant after getting dissolved in the film of water present over the cells. In the cells this oxygen oxidizes the carbohydrate and other organic compounds into carbon dioxide and water to produce energy. Some of this carbon dioxide is used in photosynthesis. The rest of the carbon dioxide and some of the water (vapours) collect in the airspace from where they pass out to the exterior through lenticels and stomata. The elimination of carbon dioxide is more evident from the parts without chlorophyll like growing seeds and buds. The water produced in this process also become a part of the already present water in the body of plants.

          As in animal the process of oxidation (respiration) in plants consists of many enzymatic reaction. This process occurs at a faster rate in the parts of the plant having rapid growth like growing seeds, buds, apical meristem of roots and shoots, because these parts require more energy to accomplish the growth process.

       The gaseous exchange in plants is not very evident during the day time as the products of respiration i.e. carbon dioxide and water are the reactants in the process of photosynthesis. So the carbon dioxide and water produced in the respiration are utilized in photosynthesis, occurring in the day light. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant from outside for photosynthesis.

 In the day time the plants therefore, takes in carbon dioxide and expel out oxygen. The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria.

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