Answer:
algae
Step-by-step explanation:
If a carbon in a molecule of carbon dioxide from the air is traced into a molecule of glucose inside a fungal cell, the carbon must have gone through an algae in order to get into the fungus.
Fungi generally do not have the ability to fix carbon dioxide through photosynthesis. However, they are able to form a symbiotic relationship with algae through an organism known as lichen.
In lichen, the fungi and the algae enter a mutually beneficial relationship in which the fungi provide moisture and nutrient to the algae and in turn, the algae provide food to the fungi out of the sugar produced from photosynthesis.
Hence, a carbon traced from the air to a fungi most likely passed through an algae as a result of symbiotic relationship between the two organisms.