Which of the following is not used single cell protein (SCP)?

The correct answer is Option (4) → Gracilaria

Single cell protein (SCP) is protein-rich food made by growing microbes on a large scale.

Option (1) Methylophilus methylotrophus — Used as single cell protein. This bacterium multiplies so fast that 250 g of it can make about 25 tonnes of protein in a day.

Option (2) Chlorella — Used as single cell protein. A unicellular green alga, grown as a protein-rich food supplement.

Option (3) Spirulina — Used as single cell protein. This blue-green alga grows on waste water, straw, molasses and even sewage, and gives food rich in protein, minerals and vitamins.

Option (4) Gracilaria — Not used as single cell protein. Gracilaria is a multicellular red alga (a seaweed), used as a source of agar, not grown as SCP.

Note: This question is from Chapter 9, Strategies for Enhancement in Food Production, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 9, Strategies for Enhancement in Food Production):
Single Cell Protein (scp) – “… Microbes are being grown on an industrial scale as source of good protein. Blue-green algae like Spirulina can be grown easily on materials like waste water from potato processing plants (containing starch), straw, molasses, animal manure and even sewage, to produce large quantities and can serve as food rich in protein, minerals, fats, carbohydrate and vitamins. Certain bacterial species like Methylophilus methylotrophus, because of its high rate of biomass production and growth, can be expected to produce 25 tonnes of protein.”