Fungi are heterotrophic because they lack chlorophyll. Chlorophyll is the green pigment found in plants that allows them to produce their own food through photosynthesis. Since fungi do not have chlorophyll, they cannot produce their own food like plants do. Instead, they obtain their nutrients from other organisms, either living or dead. This means that they have to feed on organic matter to survive, making them heterotrophic. Therefore, we can say that fungi are heterotrophic because they lack chlorophyll and cannot produce their own food through photosynthesis, so they must obtain nutrients from other sources.