Final answer:
Water-soluble substances pass through the plasma membrane via integral proteins, which can be channels or carriers facilitating the movement of these polar molecules.
Step-by-step explanation:
The passage of water-soluble substances through the plasma membrane is made possible by integral proteins in the membrane.The structure of the plasma membrane is integral to its function in regulating the entry and exit of materials. Lipid-soluble substances can easily move through the hydrophobic lipid bilayer, but water-soluble substances, which are polar, cannot do so as readily. This is where integral proteins play a critical role. These proteins are embedded in the plasma membrane and may form channels that provide a hydrated path for polar and charged substances to pass through or function as carriers that specifically bind to substances and facilitate their diffusion across the membrane.
Transport proteins, which are a type of integral protein, can be categorized into channels and carriers. Channels, like aquaporins, allow for a high rate of water passage, serving as a tunnel through which water molecules can traverse. Carriers change shape to move a bound substance across the membrane, enabling the selective transport of various substances.