Final answer:
Option (b), Microbial plastics are primarily composed of polyhydroxyalkanoates (PHAs), which are polyesters produced naturally by microorganisms like bacteria for energy storage, and not of polysaccharides, polyaromatic hydrocarbons, nor xenobiotics.
Step-by-step explanation:
Microbial plastics, also known as bioplastics, are primarily composed of polyhydroxyalkanoates (PHAs). These are polyesters produced in nature by numerous microorganisms, such as bacteria. PHAs are synthesized by these microbes as a form of energy storage and can be used to produce plastics that are biodegradable.
Options such as polysaccharides and polyaromatic hydrocarbons represent different classes of compounds; polysaccharides are carbohydrate polymers and are commonly found in the extracellular matrix of biofilms, while polyaromatic hydrocarbons are organic compounds containing multiple aromatic rings and are not typically used to make plastics.
Xenobiotics, on the other hand, refer to substances that are foreign to a biological system, often derived from human activities, and include materials such as pesticides, drugs, and various industrial chemicals. While microbes can degrade these xenobiotics via bioremediation, they are not used to make microbial plastics.