Comparison of different transport mechanisms

This statement is partially true. Transpiration pull is the major factor which facilitates movement of water in xylem. But there are other factors at play. The cohesion-adhesion and surface tension gives high capillarity to water molecules which enables it to reach a certain height in plant's xylem. Transpiration pull has an augmentative effect on the surface tension push. So in totality it is cohesion-adhesion-surface tension and transpiration pull which does the whole function of transporting water to greater heights in plants

Root pressure can provide only modest push during water transport in plants. The main role of root pressure is in re-establishing the continuous chain of water molecules in the xylem. The continuous chain often breaks due to enormous tension created by transpiration pull.

(a) Cohesion: Mutual attraction between water molecules is called cohesion.
(b) Adhesion: Attraction of water molecules to polar surfaces is called adhesion.
(c) Surface Tension: Water molecules are attracted to each other in the liquid phase more than to water in the gas phase. This gives a liquid an ability to acquire the least possible area and explains the spherical shape of raindrops.
These properties give water high tensile strength, i.e., an ability to resist a pulling force, and high capillarity, i.e., the ability to rise in thin tubes. In plants capillarity is aided by the small diameter of the tracheary elements - the tracheids and vessel elements.

Evaporation from the leaf sets up a pressure gradient between the outside air and the air spaces of the leaf. The gradient is transmitted into the photosynthetic cells and on the water-filled xylem in the leaf vein. This facilitates movement of water from xylem to the guard cells of stomata

Significance of transpiration:
1.Transpiration pull facilitates movement of water from roots.
2.Transpiration supplies water for photosynthesis
3.It pulls minerals from soil.
4.Helps in cooling of plants.
5.Maintains shape of plant cells

Desert plants have a different mechanism of photosynthesis and it is called C₄ pathways. The evolution of the C₄ photosynthetic system is probably one of the strategies for maximising the availability of CO₂ while minimising water loss. C₄ plants are twice as efficient as C₃ plants in terms of fixing carbon (making sugar). However, a C₄ plant loses only half as much water as a C₃ plant for the same amount of CO₂ fixed.

Membrane proteins provide sites at which movement of certain molecules takes place. These molecules have hydrophilic moiety and hence it is difficult for themto cross a membrane. They need assistance of membrane proteins to cross the membrane. This is called facilitated diffusion.

(i) Sugars and amino acids are transported by phloem tissue, i.e., ' .part B which are found alternating between the central core of xylem tissue.
(ii) Direction of Transport'.

I - Uniport transport
II - Antiport transport, 
III - Symport transport.

The rate of transpiration will be maximum when the soil is humid and atmosphere is dry because of following reasons.
(i) Availability of more water in the soil is necessary for the absorption of water by the roots in order to carry it up to the xylem. Thus, lack of water decrease transpiration and over all health of the plants. Whereas, more water in soil increase transpiration.
(ii) In dry climates, transpiration is increased. Water is forced to diffuse more rapidly in to the air due to the concentration difference between the environment outside the plant. Low humidity  creates a vapour gradient between the plant and the air.In dry air, there is lack of water, forcing water to be pulled from the plant to the atmosphere increasing transpiration. Therefore, in humid climates, transpiration is less affected by diffusion.

Turgor pressure maintains rigidity of a plant cell, i.e., it keeps plants upright and stiff.
It also plays an imporant role in plant cell growth whereby the cell wall undergroes irreversible changes in volume and structure.
It also influences the opening and closure of stomata by influencing the turgidity of guard cells.

If a pressure greater than atmospheric pressure is applied to pure water or a solution, its water potential increases. It is equivalent to pumping water from one place to another. Pressure can be built up in a plant system when water Enters a plant cell due to diffusion against the cell wall. It makes the cell turgid, this increases the pressure potential. Pressure potential is usually positive and denoted by \({ \Psi }_{ p }\).