How does water reach plants from the soil? Can it go aginst the gravitational laws?

Question

I dont think there is any other theory except the suction theory which explains this.

Answer 1

Trees do NOT get water to their leaves using cappilary action alone. Cappilary action could lift water to maybe 10 metres maximum. The tallest trees are over 8 times that height. Cappilary action plays only a small, albeit vital, role in lifting water in trees.

The simple answer is that the tree uses the equivalent of a siphon effect to lift the water. A siphon works because water is cohesive, IOW water sticks to water. That cohesiveness of water in a siphon tube means that as water at one end falls it is able to suck more water up from the other end. Provided that the fall is greater than the rise you are trying to overcome you can use a siphon to lift water to significant heights.

A tree trunk is basically composed of masses of siphon tubes filled with water, but it doesn't have any physical 'fall' component. Instead what the tree uses is the force generated by evaporation. As water enters a leaf it is exposed to the air and allowed to evaporate. Because water is cohesive that loss of water creates a negative pressure that pulls more water into the leaf within the leaf, and that in turn creates a negative pressure that pulls water into the vessel elements of the branch and the trunk. That pressure is sufficiently high to lift water to the tops of the tallest trees.

Which is why trees use such massive quantities of water. Even a small tree will use over 100 litres of water a day and less than 1% of that will be used physiologically. The rest is simply evaporated off to draw more water up the stem. It's an incredibly wasteful process.

This is also the reason why trees in dry environments are invariably shorter than plants in wetter environments. Because the system functions like a siphon the water column in the trunk can never be allowed to break or the pressure inside will immediately drop to zero. It's like getting vapour lock in a fuel line and plants can't re-prime the line. There has to always be sufficient water in the ground to feed the negative pressure required in the column. The taller the tree the greater pressure required and hence the more water required. As a result the maximum height of tree is determined in large part by the amount of water available.

Answer 2

The problem was debated in the botanical circles for a long time and ultimately a theory advocated by Dixon has been accepted by and large. This will be a valid theory till some new and more satisfactory explanation is put forth by some one, as the science is always in the quest of eternal truth..

The theory is known as Dixon’s Theory of Ascent of Sap.
According to this theory not any single factor, but four factors in combination lift the water to great height.
These four factors are explained below in brief.

1) Osmosis Or Endosmosis – This factor is responsible for the lateral movement of water from the soil, across the cortical tissue in to the water conducting xylem elements.
a) Root hair are unicellular living cells, they absorb water from the soil by a process called osmosis and pass it on to the other living cells LATERALLY in the cortex or the middle zone of the root. All the cells involved are living as only a living cell with a cell membrane or plasma membrane can show osmosis.
b) The water thus absorbed, passes through the pericycle and enters the xylem element, which is a dead tissue.
c) No upward movement of water is involved in this phase.
d) The roots are spread far and wide below the soil surface always in the quest of water. This is more so in the case of trees. For any given plant the total surface area of the root system is far far greater than that of the shoot system and that is precisely for water absorption.

2) Transpiration Pull – This factor is responsible for the UPWARD movement of water in the direction of the leaves.
a) The loss of water from the surface area of the leaves is called transpiration.
b) As the leaves transpire water there is a water deficit in the leaves. To make good that deficit the water is pulled up from the adjoining tissue in to the leaves. This is precisely called transpiration pull.
c) If there is no enough water then the leaves begin to wilt and dry. And it is a matter of common observation. That is why the crop plants or pot plants require regular watering.

3) Cohesive Force of Water Molecules – The ability of water molecules to remain clinging together is due to the force of cohesion between them ( i.e. mutual attraction) .
a) When one opens a water tap, water comes in a form of a continuous stream and not in a form of a molecule after a molecule. This is precisely due to the force of adhesion. It is exhibited by many other chemicals besides water.
b) Xylem elements in a plant / tree form a CONTINUOUS system of water pipes through out . It forms an interconnected network with in the plant / tree. It is because of this , there is a continuous water column
(even though highly branched) within the plant body.
c) Due to the ‘Transpiration Pull ‘ this water column is constantly pulled in the direction of the leaves like a massive rope being winched UPWARDS!
d) This water column will not break no matter what the height of the tree is . This is because the cohesive force of water molecule will require more than 120 atmospheric pressure to break it!

e) Thus water can rise easily to a height of 400 feet.
f) The tallest tree in the world, the Red wood giant or Sequoia semiperviens is about 384 feet!

4) Force of Adhesion between water and the walls of the xylem elements—Xylem elements are made up of lignin . There exists a force of attraction between it and the water . This is the force of adhesion.
( i. e. attraction between to dissimilar things.)
This leads to the capillary action and makes the water column continuous and stronger.
Only capillary action cannot account for the rise of water to great height . As Taller trees have wider Xylem ( It is contrary to the expectation.).

Answer 3

There are many other theories which explains how water reach plants from soil like:-
1. Capillary force theory.
2. Relay pump hypothesis.
3. Root pressure theory etc.

Answer 4

Plants use capillary action to draw water up from the soil. In a sufficiently thin tube, adhesive forces between a fluid and a solid (the walls of the tube) can overcome cohesion within the fluid as well as gravity, causing the fluid to bulge upwards and flow into the tube.

Answer 5

Ive heard that their soil can in fact grow earth plants, they might have to add extra nutrients and stuff though.... There is interesting this video about colonization of mars that will hapen in the somewhat near future I dont know the name of it but just search for it on youtube or google its a pretty big project

Answer 6

acc. 2 the dixon and jolly theory there is a continous column of xylem in the whole plant wid no space for air bubbles to enter. and this is enough to create a pressure wid whicvh water has been experimenttally shown to carry water to 60 m height thru a continous column of cappilaries.when the water is being continouslylost thru the process of transpiration this contanous column conducts water to heights against gravitational pull.

Answer 7

Plants have roots in the SOIL. That is how they get their water (and nutrients). To over simplify, if you put a straw in a glass of water and suck, you will pull the water into yourself regardless of gravity. Plant roots do this in a manner more like osmosis called capillary action, but I think you can get the idea.

Answer 8

there are 3 ways by which water reaches the plants from the soil.one by root pressure, two by cohesion theory or transpirational pull and three by capillary action.it can go against the gravitational laws.

Answer 9

No water mainly reach at top by transpiration pull passively and agaist a potensial gradient actively by the release of salt in xylem.

Answer 10

Diffusion. The water is absorbed by the dirt in the area and it spreads out evenly from the source of the water in every direction. - theory 1

Another theory is that the dirt as it mixes with the water displaces the water similar to the way an ice cube would in a glass of water. - theory 2

But the most reasonable is that rain falls and as the water drains into the ground it gets to the roots.