Which process is performed by microorganisms used in the production of Single Cell Proteins $(SCP)$?

Single cell protein is an alternative protein source for animal and human nutrition formed from certain beneficial microorganisms like

Give information about $SCP$.

What does Single Cell Protein $(SCP)$ help to reduce?

Which approach of genetic engineering is considered important for reducing environmental pollution?

Consider the following statements $(I-IV)$ and select the option containing the correct answer.
$I.$ The unicellular $Spirulina$ can produce large quantities of food rich in protein,minerals,and vitamins.
$II.$ Based on body weight,the microorganism $Methylophilus$ $methylotrophus$ can produce much more protein in a day than a cow.
$III.$ Common button mushrooms are a rich source of Vitamin-$C$.
$IV.$ $A$ variety of rice has been developed that is rich in calcium.