Question

Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs. What are microbes referred to as? How do the microbes fulfill their energy requirements? 

Answer 1

On the basis of nutrition, organisms are classified as autotrophs and heterotrophs: Autotrophs are further categorised into photoautotrophs and chemoautotrophs, while heterotrophs may be parasite pred or a saprophyte etc. 
Microbes are saprotrophs and derive nourishment or energy from dead organic matter 0: remain of plants and animals and this digestion is extracellular.