Transportation of Food and Water

Transportation in plants

Transportation means the movement, movement of anything. But here we are describing the movement in the plant body. Ether the movement of food or movement of water in the plant body. First of all, we describe here the transport of water in plant.

Transport of Water

For many years ago in botany, it has been studies, the process by which water raised to considerable height in plants. The result of this research is “cohesion-tension theory”.

According to this theory, the force which carries water and dissolved many useful materials for plant goes upward through xylem is Transpirational pull. This process creates a pressure difference that pull water and salts & minerals up from roots. when the leaf losses water, the concentration of water of its mesophyll cells drops. This drop causes pressure difference and water moves upward by osmosis from the xylem of leaf into mesophyll cells. When one molecule of water moves up in the xylem of leaf, it creates a pulling force that continues all the way to root. This force of water is called Transpirational pull. It causes water to move transversely from root epidermis to cortex and pericycle.

Reason of creational Transpirational pull

1. Water is held in tube(xylem) that has small diameter
2. Water molecule adhere to the wall of xylem tube (adhesion)
3. Water molecule cohere to each other (cohesion)

Transportation of Food

In transportation of food phloem is responsible throughout the plant body. that’s why it is called “food street” of plant. The glucose formed during the photosynthesis in mesophyll cells is used in respiration and excess of it is converted into sucrose. In most plat food is transport into sucrose form. “Pressure-flow mechanism” hypotheses describe the transportation of food in plants in pressure flow mechanism, food moved from sources to sinks. Sources including the exporting organs, typical mature leaf or storage organ. Sinks are the area of active metabolisms e.g. roots, developing fruits.

At source, food(sugar) is moved by active transport into sieve tubes of phloem. Due to pressure of sugar in sieve tubes, their solute concentration increases and water enter them from xylem (via osmosis). This result in higher pressure of water in these tubes, which drive the solution of food toward sink.

At sink end, food is unloaded by active transport. Water also exits from the sieve tubes. The exit of water decrease pressure in sieve tubes, which causes a mass flow from the higher pressure at the source to the now lowered pressure at the sink.