Transportation Introduction

In unicellular organisms a single cell carries out all the life processes as the cell itself is the organism. In advanced forms like the few-celled algae, protozoa, sponges, etc., the size of the organism ensures that all the cells are not very far from each other. The uptake of materials from the environment is through the general body surface and the transport within the cells is by diffusion and the transport from one part of the body to the other is by cell to cell movement of substances. However, more advanced multicellular forms need a transportation mechanism. The sites of absorption and synthesis are very specific and are separated by a greater distance from the other parts of the body.

The actual movement of materials into the individual cells is by diffusion, osmosis or active transport.

The above processes are common to plants and animals for entry of substances into the individual cells. However, the transport of materials across the plant or animal body occurs by processes broadly called the mass flow system. The mechanism of mass flow is very different in plants and animals because of the basic differences between them. This mass flow system is called the vascular system. Vascular system consists of tubes that transport fluids from one part of the body to another.

Transport in plants relies mainly on physical processes whereas transport in animals utilises muscular energy. Whatever be the actual process of transportation, they are all in some way dependent on the existence of concentration gradient.

Concentration gradient is the difference in the concentrations of a particular substance. The natural tendency is for the substances to move from the region of higher concentration to the region of lower concentration. This is called moving along the concentration gradient. Movement against the concentration gradient (from lower to higher concentration) requires energy. For example, in plants, water is transported from roots (where it is absorbed and therefore more in concentration) to the leaves where it is less in concentration. In animals, oxygen in transported from lungs, where it is in high concentration to the cells of the body where it is in lower concentration.

In plants, the vascular system consists of vascular tissue made up of xylem and phloem. In animals, the vascular system, also called circulatory system, is made up of vascular (connective) tissue - blood and lymph.