Aquaporins are integral membrane proteins. These form pores or channels in the membrane. The water can flow more rapidly through these pores to inside of the cell, as compared to the process of diffusion.

These are plumbing systems of the cells. These selectively conduct water in and out of the cells, while preventing the passage of ions and other solutes.

A. Stress hormone ABA (Abscisic Acid) gives signals to stomata to get closed, whenever there is scarcity of availability of water to the plant. This prevents the loss of water through transpiration by leaves. It also increases the tolerance of plants to various kinds of stresses.

B. It (ABA) is released or transported from stem apices to leaves.

Plants can get rid of excess water by increasing the transpiration rate but upto a certain limit. Prolong water logged conditions for roots may lead to the death of the plant (as they can not respire).

Difference between diffusion and translocation in plants is as follows

Diffusion	Translocation
It is the movement of solute from higher concentration to lower concentration.	It is movement of organic compounds mineral salts from one part of the plant to another.
No energy consumption involved.	It is energy consuming process.

Difference between diffusion and facilitated diffusion is as follows

Diffusion	Facilitated Diffusion
In diffusion, molecules move in a random fashion, the net result being substances moving from regions of higher concentration to regions of lower concentration.	The diffusion of substance against a concentration gradient, which is facilitated by the proteins is known as facilitated diffusion without expenditure of ATP energy.
Diffusion is a slow process and is not dependent on a 'living system'. No expenditure of energy takes place.	The porins proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allow molecules up to the size of small proteins to pass through.