Filtered water, a branch away?

• In India, more than one in ten households still lack sufficient and clean drinking water, according to the 69th round of the National Sample Survey.
• Filter water using plant xylem is new research. 
• In this tests conducted with deionised water in which bacteria and dyes were introduced, the xylem filter effectively removed both when subjected to pressure.
• Xylem is a transport tissue in vascular plants that conducts water and dissolved nutrients upwards from the roots. 
• Tracheids, which are cells in the xylem, are shorter and have smaller diameters in conifers, thereby offering higher resistance to flow but a greater cross-sectional area of the stem to conducting xylem tissue. 
• This likely makes it the most suitable xylem tissues for filtration at the micron or larger scale.
• This filter should work with real-world water samples as long as it is not highly turbid. 
• Turbidity tends to clog filters, and this one is not an exception.
• The researchers prepared the xylem filter by removing the bark of pine tree branches and then inserting it into a tube. 
• The pressure that was used for this study suggests that it is easily achievable using a gravitational pressure head. 
• The device construction therefore seems to be simple, considering that the wood might have to be replaced often. 
• “The idea is that these filters should be inexpensive enough to dispose off rather than attempt to clean them.

Challenges-

• It is important to note that these filters are still in their nascent stages. 
• Identifying locally available sources of xylem, testing the flow through xylem of different plants, improving the rejection of viruses up to nanoparticles are some of the challenges that lay ahead.

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Information About XYLEM:

Xylem is one of the two types of transport tissue in vascular plants (phloem is the other).

Its basic function is to transport water, but it also transports some nutrients.

Structure

• The most distinctive xylem cells are the long tracheary elements that transport water. 
• Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels.
• Xylem also contains two other cell types: parenchyma and fibers.
• Xylem can be found:

1. in vascular bundles, present in non-woody plants and non-woody parts of woody plants
2. in secondary xylem, laid down by a meristem called the vascular cambium in woody plants
3. as part of a stelar arrangement not divided into bundles, as in many ferns.

• In transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only.

Main function – upwards water transport

The xylem transports water and soluble mineral nutrients from the roots throughout the plant.

 It is also used to replace water lost during transpiration and photosynthesis. 

Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. 

The transport is passive, not powered by energy spent by the tracheary elements themselves, which are dead by maturity and no longer have living contents.

 Two phenomena cause xylem sap to flow:

• Transpirational pull: the most important cause of xylem sap flow is the evaporation of water from the surfaces of mesophyll cells to the atmosphere. This causes millions of minute menisci to form in the mesophyll cell wall. The resultingsurface tension causes a negative pressure or tension in the xylem that pulls the water from the roots and soil.
• Root pressure: If the water potential of the root cells is more negative than that of the soil, usually due to high concentrations of solute, water can move by osmosis into the root from the soil. This causes a positive pressure that forces sap up the xylem towards the leaves. In some circumstances, the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is highest in the morning before the stomata open and allow transpiration to begin.