Why are fungi genetically closer to animals than plants?
Why are fungi genetically closer to animals than plants?
For a long time in human history, fungi were classified as plants. They are stationary, grow in the soil, and often look leafy or root-like. However, modern DNA sequencing and biochemical analysis have revealed a surprising evolutionary truth: fungi are much more closely related to animals than they are to plants.
Key Evolutionary Reasons
1. Mode of Nutrition
- Plants are autotrophs, meaning they produce their own food through photosynthesis using sunlight, water, and carbon dioxide.
- Animals and Fungi are heterotrophs. They cannot produce their own food and must consume or absorb organic carbon from other organisms. While animals ingest food and digest it internally, fungi secrete digestive enzymes into their environment and absorb the broken-down nutrients externally.
2. Cell Wall Composition
- Plant cell walls are made primarily of cellulose, a tough carbohydrate that gives plants their rigid structure.
- Fungal cell walls are made of chitin—the exact same fibrous substance found in the exoskeletons of insects, crabs, and spiders.
3. Energy Storage
- Plants store their excess energy as starch.
- Animals and Fungi store energy as glycogen.
The Genetic Evidence
When scientists sequence the genomes of various organisms, they look at conserved genes, such as those coding for ribosomal RNA and proteins. Phylogenetic trees built from this genetic data consistently place fungi and animals into a supergroup known as Opisthokonta.
Plants, along with algae, belong to a completely different supergroup called Archaeplastida. This means that animals and fungi shared a common ancestor millions of years after the lineage that led to plants split off on the tree of life.