The correct answer is option 'B', which states that plastic bags do not form a part of the constituents of an ecosystem. Let's understand why this is the correct answer by examining each option and its relevance to an ecosystem.

a) Biotic constituents:
Biotic constituents refer to living organisms that are a part of an ecosystem. These include plants, animals, fungi, bacteria, and other microorganisms. Biotic factors play a crucial role in the functioning of an ecosystem as they interact with one another and with the abiotic (non-living) factors in their environment. They are responsible for energy transfer, nutrient cycling, and maintaining the overall balance within the ecosystem.

b) Plastic bags:
Plastic bags are man-made objects that are not living organisms and therefore do not fall under the category of biotic constituents. They are non-biodegradable and pose a significant environmental threat due to their persistence in the environment. Plastic bags can cause harm to wildlife through ingestion or entanglement, contribute to pollution in water bodies, and take hundreds of years to decompose. While plastic pollution has become a global concern, plastic bags themselves do not form a part of the natural ecosystem.

c) Abiotic constituents:
Abiotic constituents refer to the non-living components of an ecosystem. These include physical factors such as sunlight, temperature, water, air, soil, minerals, and chemicals. Abiotic factors play a vital role in determining the structure and function of an ecosystem. They influence the distribution of biotic components, provide habitats, and affect the overall productivity of the ecosystem. Examples of abiotic factors include sunlight for photosynthesis, temperature for metabolic processes, water for hydration, and soil for nutrient availability.

d) All of these:
This option is incorrect because it suggests that all the mentioned constituents (biotic, plastic bags, and abiotic) are not part of an ecosystem. As explained above, biotic and abiotic constituents are integral to an ecosystem, while plastic bags are not naturally occurring components of an ecosystem.

In conclusion, plastic bags do not form a part of the constituents of an ecosystem. They are man-made objects that pose environmental threats but are not living organisms and do not contribute to the natural functioning of an ecosystem.