Types of plant transport - class-XI

Pholem is the food-conducting tissue.

Roots concentrate minerals against their concentration gradient (from low concentration in soil to high concentration in the root) using active transport, which requires energy (ATP).

Water held tightly by soil particles around them is called as hygroscopic water. It is held in a very thin film and is not available to plants. Plants are able to absorb capillary water, which is present in the capillary spaces between soil particles. Run away water is also not available to plants. 

Absorption of mineral elements from the soil involves active transport by the cells. Minerals may also be absorbed as ions rather than salts.

Water transport is a physical process and not a physiological process. It does not require living cells and protoplasm. The driving force is the transpiration pull generated by loss of water through leaves. This is the reason why xylem tracheids and vessels are dead on maturity. Food transport is a physiological process and requires living cells similarly stomatal movement also is a physiological process and requires living cells.

In 1991, the Nobel prize in medicine or physiology was given to Erwin Neher and Bert Sarkmann for the discovery of single ion channels in cells. They were able to develop a technique that registers very minute variations in electric currents that passes through a single ion channel. This new method helped them to watch the activity of a single molecule.  

The minerals are mainly absorbed by roots which are in direct contact with the soil. Absorption of water is known as water uptake. Short distance transport of water takes place from cell to cell  across the membranes involving physical processes such as diffusion, osmosis and water potential differences. Long distance transport involves complex processes such as root pressure and transpiration pull. transport There are two processes by which mineral absorption takes place:

Ion channels are special proteins through which ions flow along the concentration gradient. These channels are important, because the membrane is made up of bilayer of lipids and will not allow transport of water soluble ions. However lipid soluble components can dissolve in membrane lipids and can be transported across the membrane without special carrier or transport proteins.
But all ions cannot pass through same transport protein because volume of each ion will be different. There are different transport proteins for transport of different ions.

Active transport processes move substances against their concentration gradient, which requires energy in the form of ATP. Passive processes, such as diffusion or osmosis, occur spontaneously without the expenditure of metabolic energy.

The absorption of ions, involving use of metabolic energy is called active absorption. Energy is generally obtained from ATP.Therefore active absorption is linked to hydrolysis of ATP

Active transport is typically unidirectional because it involves specific pumps or carrier proteins that move solutes against a gradient in one specific direction. While some systems may have multiple transporters, the mechanism of a single active transport pump is inherently directional.

Active transport, which is the movement of ions or molecules across a cell membrane in the direction opposite that of diffusion, that is, from an area of lower concentration to one of higher concentration, requires the assistance of a type of protein called a carrier protein, using energy supplied by ATP. So, the correct option is 'ATP'.

The mechanism used for the translocation of sugars from source to sink is called the pressure flow hypothesis. As glucose is prepared at the source, it is converted to sucrose. This is moved into the companion cells and then into the living phloem sieve tube cells by active transport. Again active transport is necessary to move the sucrose out of the phloem sap and into the cells which will use the sugar converting it into energy.