Question

Capillarity theory was proposed by
(a) Unger
(b) Sachs
(c) Boehm
(d) Mac Dougal

Answer 1

Hint: Capillarity theory was proposed to explain how water and minerals traveled across long distances i.e. from the root of the plant to its stem against the force of gravity. This theory suggests that the xylem vessels are like capillaries and thus water rises up in them.

Complete Step by Step Answer:
The capillarity theory was proposed by Boehm in 1809. He proposed that water rose up in them because of the thin diameter of the xylem vessels as is seen in capillary tubes. The thinner the vessel, the more will be the rise of water in it. There forces responsible for the rise of water are:
- Adhesion: The mutual attraction between the molecules of water i.e. attraction between the same substances.
- Cohesion: The attraction of water molecules to the polar surfaces of the tracheary elements.
- Surface tension: The attraction between water molecules is more in the liquid state as compared to the gaseous state.
So, the correct option is ‘Boehm’.

Additional information: Water, minerals, and food are moved in plants through a process known as mass or bulk flow system. This mass flow occurs on the basis of the pressure difference between two points. This pressure difference can be of two types ie.e positive hydrostatic pressure gradient (a garden hose) and negative hydrostatic pressure gradient (suction in a straw) .
The positive hydrostatic pressure is xylem is caused by root pressure.
And the negative hydrostatic pressure is caused by a process known as transpiration pull. This is because as water keeps evaporating due to transpiration, there is tension created in the xylem to pull more water upwards.

Note:
- Water and minerals are mainly transported through xylem vessels and tracheids.
- Phloem is responsible for transporting food and a variety of organic and inorganic solutes.
- Root pressure is caused by actively absorbing water and minerals from the soil.