Identify the correct statements regarding mass flow hypothesis.
(A) Mass flow is faster than diffusion.
(B) Mass flow is the result of pressure difference between the end points.
(C) Different substances involved in mass flow move at different paces.
(D) Mass flow can result through either a positive or a negative hydrostatic pressure gradient.
Choose the correct answer from the options given below :

Statement A, B and D are correct.
A. Mass flow is generally faster than diffusion. This is because mass flow involves the bulk movement of substances driven by pressure gradients, while diffusion involves the random movement of particles at the
molecular level.
B. Mass flow is indeed the result of a pressure difference between the source and sink points in a system. The
pressure gradient created between these two points drives the movement of substances in a bulk flow manner. Mass flow in the phloem tissue occurs due to the pressure gradient created by the loading of sugars (source) and their unloading or utilisation (sink) in different parts of the plant. The high concentration of sugars in the source region creates a high hydrostatic pressure, while the low concentration in the sink region leads to a lower hydrostatic pressure. This pressure difference results in the mass flow of sugars through the phloem, transporting nutrients and other substances to where they are needed in the plant.
C. Different substances involved in mass fl ow move at different paces is not correct. According to the mass
flow hypothesis, substances being transported through the conducting tissues move together as a mass, maintaining a relatively constant ratio. The movement is not based on
the individual substances moving at different rates. 
D. Mass flow can occur due to either a positive or a negative hydrostatic pressure gradient.