In the diagram, the association illustrated demonstrates

The diagram shows a cross-section of a structure that represents a lichen, which is a symbiotic association between a fungus and an alga. The fungus provides a suitable environment for the alga to grow, while the alga produces food through photosynthesis to share with the fungus. This type of relationship is known as mutualism, where both organisms benefit from the association. Mutualism is the correct answer (Option D).

In contrast to mutualism, the other options represent different types of relationships between organisms:

Parasitism (Option A): In a parasitic relationship, one organism (the parasite) benefits at the expense of the other organism (the host). The host is harmed by the relationship, while the parasite benefits.

Commensalism (Option B): This is a relationship where one organism benefits, while the other is neither harmed nor benefits. The organism that benefits is called a commensal, and the organism that is not affected is the host.

Saprophytism (Option C): This is a relationship in which an organism feeds on dead or decaying organic matter. Saprophytes, such as some fungi and bacteria, play a crucial role in breaking down and recycling nutrients in ecosystems.