Movement of Water in Plants: Methods of Transportation

Introduction

Transport means for the movement of water, gases and nutrients in plants . Diffusion is a process that takes place without any active participation on the part of the It might be from one section of the cell to another, or from one cell to another, or over short distances, such as from the leaf’s intercellular gaps to the exterior. There isn’t any energy loss. Molecules migrate at random, resulting in compounds shifting from high to low concentration zones. Diffusion is a process that takes a long time. Diffusion rates are affected by concentration gradients, membrane permeability, temperature, and pressure. It is defined as the passive movement of molecules or particles down a concentration gradient, or from higher to lower concentration areas.

Facilitated Diffusion:

Diffusion can only occur if there is already a gradient. Lipid-soluble substances move more quickly through the membrane. The passage of hydrophilic moiety compounds across the membrane is problematic. It must be made easier for them to move. Membrane proteins serve as crossing points for such compounds. Even if proteins assist molecules in dispersing, there must be a concentration gradient.

In assisted diffusion, certain proteins assist in moving things across membranes without using ATP energy. Facilitated diffusion cannot transfer molecules from a low to a high concentration since this would necessitate energy input. The rate of transfer reaches a maximum when all of the protein transporters are employed.

Active Transport:

Energy is used to push molecules against a concentration gradient through active transport. Membrane proteins are responsible for active transport. Pumps are proteins that transport molecules through the cell membrane by using energy. These pumps have the ability to move chemicals from low to high concentrations. When all of the protein transporters are utilised or saturated, the transport rate reaches its maximum.

Active transport is a kind of transport in which ions or molecules move against a concentration gradient, i.e., movement in the opposite direction of diffusion, or migration from a lower to a higher concentration region.

Movements of water in plants 

(a) Water Potential:

The idea of water potential is crucial to comprehend the flow of water. Kinetic energy may be found in water molecules. They move in a random, fast and continual motion in liquid and gaseous form. The larger the water potential, the higher the concentration of water is pure water. As a result, water will flow from a system with a greater water potential to one with a lower one.

(b) Osmosis:

The plant cell is surrounded by its cell membrane and cell wall. Because the cell wall is permeable to water and other compounds in the solution, it does not act as a barrier to movement. Osmosis is the process of water diffusion over a differentially or semipermeable membrane. When a driving force is applied, osmosis occurs. Both the pressure gradient and the concentration gradient affect the net direction and rate of osmosis.

(c) Plasmolysis:

When a cell is put in a solution that is hypertonic to the protoplasm, this happens. Plasmolysis is a reversible process in most cases. Water diffuses into the cell when it is put in a hypotonic solution, causing the cytoplasm to build up turgor pressure against the cell wall.

Water diffuses out of a plant cell when it is immersed in a highly concentrated solution, and turgor pressure is decreased, causing the cell to become flaccid. Additional water loss will cause plasmolysis and, eventually, cytorrhysis (total cell wall collapse).

(d) Imbibition:

Imbibition is a kind of diffusion in which water is absorbed by solids or colloids, creating massive volume increases. Imbibition may be seen in the absorption of water by seeds and dry wood. Because water moves along a concentration gradient, imbibition is also diffusion; seeds and other similar things have very little water, therefore they absorb water quickly. The imbibition of liquids requires a water potential gradient among the liquid ingested and the absorbent. 

(e) Long Distance Transport of Water:

A mass or bulk flow system is used to carry water, minerals, and food. The movement of bulk or en masse material from one site to another as a result of pressure differences between the two points is known as mass flow.

Mass flow is characterized by substances being swept along at the same rate, whether in solution or suspension, as in a flowing river. Translocation refers to the mass transport of substances, such as the movement of water and minerals in plants, via the conducting or vascular tissues of plants

(f) Symplastic movement

The movement of water from cell to cell through plasmodesmata is known as the symplast pathway. It doesn’t make it into the vacuoles of the cells. Plasmodesmata join the cytoplasms of neighbouring cells. Individual cell cytoplasmic streaming facilitates symplastic mobility.

Various methods of transportation

The transportation of gas, nutrients, food and mater, occurs through a variety of mechanisms, here are some of them:

(i) Method of Plant Absorbing Water:

The root hairs, which are found in millions at the tips of the roots, are responsible for the absorption of water and minerals. Root hairs are slender, thin-walled extensions of root epidermal cells that dramatically enhance absorption surface area. Water and mineral solutes are absorbed only by diffusion by the root hairs.

(ii) Water Movement up a Plant:

Root pressure is the positive pressure that pushes water up the stem to tiny heights. Excess water collects in the form of droplets around special openings of veins near the tip of grass blades and leaves of many herbaceous parts during the night and early morning while evaporation is little and extra water is collected in the form of droplets covering specific openings of veins close to the edge of grass blades and leaves of various herbaceous parts. Guttation is the term for water loss in the liquid phase. 

(iii) Transpiration:

The movement of water from roots to leaves is experienced in transpiration. The evaporative loss of water by plants is known as transpiration. In addition to the loss of water vapour by transpiration, the leaf also exchanges oxygen and carbon dioxide through holes known as stomata. Stomata are often open throughout the day and close at night. Each guard cell’s inner wall is thick and elastic as it approaches the pore or stomata opening. Temperature, light, humidity, and wind speed are all elements that influence transpiration.