Explanation:
The label A represents mitochondria.
The mitochondria is also called the powerhouse of the cell which converts glucose to energy rich molecules of ATP.
Label B represents nucleus.
Nucleus contains the genetic material or DNA, RNA , nucleolus, chromatin fibres and proteins. It contains the chromosomes which control the hereditary characteristics.
Label C represents lysosome.
Lysosomes contain digestive juices which breaks down large cell parts and large molecules and helps in intracellular digestion.
Label D represents rough endoplasmic reticulum having ribosomes.
The rough endoplasmic reticulum provides surface for protein synthesis. It is also used to transport cellular contents from one cell to another.
The answer to your question is actually quite simple. If there was a sudden decrease of Fungi the environment would be filled with more dead things. Not just that, but it would also smell terribly. Just think of it like this: Fungi is basically like garbage collectors. They will recycle the stuff that you dont need and or want.