Every normal person can wonder how the water travels from the roots towards the top of tall plants. Well, it is just science.
Water travels through some long, thin tubes that run up from the roots to the stems and leaves; these tubes are called xylem. It runs in these vessels through a process called capillary action. The combination of transpiration and capillary action delivers the water from the bottom to the top of a plant.
In leaves, there are pores called stomata. These pores allow the leaves to breathe. All the excess water is excreted through them, and the wind helps to pull it out. But, because this causes a decrease in pressure – As a result, water gets pulled up in the tubes of the tree (xylem). This mechanism is called “capillary action”.
Capillary action occurs because water has the properties of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances). These properties produce the sticky nature of water. To understand this, let’s take an example that if you dip a paper towel into a glass filled with water, it climbs onto the paper towel.
But, the process of capillary action depends on atmospheric pressure levels. These levels on the surface of the water can raise the water in a hollow tube up to a height of 33 feet only. Whereas, some trees are up to ten times taller. So, it is obvious that ‘pumping’ of water in such cases is done by some other forces.
Following are the two processes that are responsible for carrying out water flow in taller trees:
In an actively growing plant, water is continuously evaporating from the surface of leaf cells that are exposed to air. This water is replaced by additional absorption of water from the soil. Water spreads through the plant from the soil to the leaf cell surfaces where it is converted from a liquid into a gas through the process of evaporation.
The cohesive properties of water allow the column of water to be ‘pulled’ up through the plant as water molecules are constantly evaporating from the leaf surface.
Let’s understand the chemistry behind the cohesive properties of water as they play a crucial role in the process of water transport.
Each molecule of water is made of one atom of oxygen and two atoms of hydrogen. Water molecules are not found singly or in small isolated groups. But, its one molecule attaches to the second and the second to the third and so on.
Due to this bonding property, a drop, a lake, a river, or a sea is formed. This natural bonding is the result of the neutral charge of water. Between the two atoms of hydrogen, there is hydrogen bond with a positive electric charge. Whereas at the other end, the charge is negative. Wherever asymmetrical electrical charges of two molecules meet, bonding is bound to take place due to mutual attraction.
2. Root Pressure
This is the force that helps to drive fluids upward into the water-conducting vessels.Root hair cells take up minerals by active transport. This is because the soil has higher water content than the cell sap of root hair. Therefore, water diffuses into the root hair.
The root hair cells then get higher water concentration than the adjacent cells of the cortex. As a result of this, water diffuses into the cortical cells. After a long chain, water is forced into the xylem tubes.
This root pressure is primarily generated by the osmotic pressure of the root cells. You can easily appreciate it from exudation of fluid when the stem is cut off just aboveground.
The chemical attraction is another force which assists this process. Roots of the tree absorb salts in the soil which make the water inside saline in nature. As salt content in the rainwater is low, it flows towards saline water of the roots. This is just a simple principle of chemical attraction that ensures the efficient water flow in trees.
To summarize, we can say that the roots of tall trees, such as the coconut palm tree, push the water upwards with the help of a vessel system along with some special forces.