In this article we will discuss about the translocation and digestion of food in plants.
Translocation and Storage of Food:
Water with dissolved mineral matters is absorbed and conducted upwards through the xylem elements to the leaves. Leaves are, in fact, the organs where complex organic food matters are mostly synthesised. Food matters are consumed particularly by the actively growing regions in simple soluble forms.
As plants manufacture in excess of immediate need, the surplus food moves to the storage regions, to be stored up for future use. When necessary the stored food becomes available for nutrition.
As the seat of manufacture is quite away from growing region and storage region, there must be arrangement for translocation of food. This transport takes place through the complex tissue, phloem, the sieve tubes taking the most active part. For storage, simple soluble food matters are converted into their complex insoluble forms and they remain as such.
The parenchymatous cells of pith, pith rays and cortex store food matters. Many plant organs are specially adapted for the purpose. Modified roots like radish, carrot, sweet potato, ginger, potato and other modified stems, fleshy leaves, bulbils, inflorescence of cauliflower store food matters.
The seeds invariably have accumulated food in cotyledons or endosperm, what is converted into simple forms to be utilised by the growing embryo during germination.
Digestion and Assimilation of Food:
Food matters mostly remain stored up in the plants in complex insoluble forms. For utilisation and translocation they are changed into simple soluble matters. Digestion is the process of converting complex insoluble food matters into their soluble and diffusible forms, so that they may be properly utilised. Thus starch is converted into sugar, proteins into amino acids and fats into fatty acids and glycerine.
Digestion may be intracellular or extracellular. In the former type, what is, in fact, common in plants, digestion takes place inside the cell. In extracellular digestion food matters are digested outside the cell and the products are used by the cell. The insectivorous plants and some fungi have extracellular digestion.
Digestion is really a process of hydrolysis, a chemical process, when complex matter is rendered simple by addition of water. It is mainly accomplished by the digestive juices, enzymes, which are complex organic colloidal substances secreted by protoplasm.
They have the power of greatly accelerating the rate of breaking down complex food matters into their simple form without themselves being used up during the process.
Thus they are organic catalytic agents. Action of enzyme is specific, i.e. each enzyme acts on one specific group of substance. Enzymes catalysing starch into sugar have no action on proteins or fats. Enzyme reactions are sometimes reversible.
Those which catalyse breaking down of starch into sugar are also instrumental in synthesis of starch out of sugar. A few common enzymes are: diastase, which converts starch ultimately into sugar; protease, which breaks down proteins into amino acids; and lipase, which catalyses fats into fatty acids and glycerine.
The digested foods are mostly transformed into protoplasm. This process involving an actual incorporation of non-living matters into the living substance is known as assimilation. It is the final stage to find the ultimate goal of constructive metabolism. The process of actual transformation is not clearly known. Assimilation results in production of more protoplasm that is needed for growth and repair.