Final answer:
The vesicular transport model has issues such as the requirement of energy in the form of nucleotide triphosphate hydrolysis and the complexity of the molecular interactions involved in processes like endocytosis and exocytosis.
Step-by-step explanation:
The issues with the vesicular transport model primarily involve its complexity and the energy requirement. One key issue is that it requires nucleotide triphosphates to be hydrolyzed to provide the energy for transporting macromolecules like proteins and large particles across the cell membrane. In processes such as endocytosis and exocytosis, other molecular players like clathrin can be involved in receptor-mediated endocytosis, which indicates that vesicular transport is not simply a matter of vesicles fusing with the plasma membrane but also involves a series of complex molecular interactions.
Another concern is that vesicular transport may sometimes include a form of motion known as hop diffusion, which requires extra kinetic energy and stands in contrast to the Brownian motion suggested by the classic fluid mosaic model of cell membranes. This additional requirement for energy highlights the active nature of vesicular transport.
Methods of Vesicular Transport
There are two primary types of vesicular transport: endocytosis, which brings substances into the cell, and exocytosis, which moves them out. Within endocytosis, there are also different mechanisms, such as phagocytosis, which engulfs large particles, and pinocytosis, which ingests fluids with dissolved particles.