 
Roots: Nature's Drillers
 In order to survive, plants need to carry out photosynthesis, and for that they need the water and minerals they take from the soil. To meet these needs, they require the roots which drill under the ground. The job of the roots is to spread rapidly underground like a net and draw up water and minerals. As well as this, plant roots, despite their delicate structure, enable plants which can weigh up to tons to hold on to and fix themselves in the soil. The soil-gripping nature of roots is most important, because it prevents landslides and the fertile upper layers of soil being washed away by the rain, and other unwanted occurrences that can adversely affect human life.
Roots need no equipment for all this. They have no engine to provide the power to start the process of water-drawing. Neither is there any equipment to pump the water and minerals to the stem, meters away. But roots can spread over a wide area and draw water. So, how do they do it?
The Pressure System in Plant Roots
When the internal pressure in root cells is lower than the outside pressure, plants take in water from outside. Another way of putting it is that they take water from outside only when they need it. The most important factor establishing this is the amount of pressure produced by the water in the roots. This pressure has to be balanced with that outside. For this to happen, the plant needs to take in water from the outside when the amount of internal pressure falls. When the opposite happens, when the inside pressure is higher than the outside, the plant gives off water from inside itself by means of its leaves to re-establish the balance.
If the level of the water in the soil were slightly higher than normal, the plant would continually take in water, because the external pressure was higher, and this would eventually damage it. If it were a little lower, on the other hand, the plant cell could never take in water from the outside because the external pressure would be low. It would even have to give off water to maintain the pressure balance. In either case the plant would dry up and die.
This shows to us that plant roots contain a balance-control mechanism to enable them to regulate the level of pressure needed at a precise moment, neither more nor less.
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