Essential requirement of an artificial medium in which explant is being regenerated is that medium must provide a carbon source such as sucrose and also inorganic salts, vitamins, amino acids and growth regulators like auxins, cytokinins, etc.

(i) Single Cell Protein (SCP) is protein rich microbial biomass which can be used as food and feed. SCP has all essential amino acids. Fat content is low. Both autotrophs and heterotrophs are used as SCP. Amongst autotrophs. Spirulina has become an important food supplement which is used in various forms including tablets. It has 60% protein, all minerals, vitamins and unsaturated fats. Amongst heterotrphs, yeast and mushrooms are being raised as SCP. There is an increasing use of low cost organic matter (saw dust, paddy husk and or organic wastes) for raising SCP like Fusarium graminearum and common mushrooms.
(ii) Soil. Microbes take part in formation and maintenance of soil. (a) They add organic matter to freshly formed soil.The process is called humification. (b) They act as scavengers and remove orgainc remains. (c) Microbes take part in biogeochemical circulation. (d) Some microbes act as biofertilizers and biopesticides.

A. Mellifera or European' bee is very common all over  Europe. Its Italian variety has been introduced in India and cross between Indo-Italian swarm yields higher amount of honey.
Merits of A. mellifera are :
(a) It has high honey collection capacity and yields more honey.
(b) It is stingless, hence easy to handle.
(c) It breeds at faster rate.
(d) It has less tendency for swarming, hence stays in given beehive for long periods and breeds very well.