Which polysaccharide, found in red algal cell walls, is a useful solidifying agent?
1) chitin 2) cellulose 3) phycoerythrin 4) agar
The correct answer and explanation is:
The correct answer is 4) agar.
Agar is a polysaccharide found in the cell walls of red algae, particularly in species of Gelidium and Gracilaria. It is commonly used as a solidifying agent in microbiological media and in food production. Agar is a gelatinous substance that has the unique ability to remain solid at a wide range of temperatures, which makes it especially useful for creating solid surfaces for growing bacteria and other microorganisms.
Agar is primarily composed of two polysaccharides: agarose and agaropectin. Agarose is the component responsible for its solidifying properties, forming a gel when dissolved in boiling water and then cooled. This ability to form gels has made agar a versatile tool in laboratories and kitchens. In microbiology, agar is used to create a stable, non-nutritive medium for growing cultures of bacteria, fungi, and algae. Its ability to remain solid at body temperature (around 37°C) allows for the growth of organisms without the medium melting.
In food production, agar is also used as a thickening agent and in the making of jellies and desserts. Agar has several advantages over gelatin, another commonly used gelling agent. It is plant-based, which makes it suitable for vegetarians and vegans. Additionally, it has a higher melting point than gelatin, so it remains firm at higher temperatures, making it useful in certain types of confectionery.
In contrast, chitin is found in the exoskeletons of arthropods, cellulose is a major structural component of plant cell walls, and phycoerythrin is a protein found in the pigment complex of red algae that helps in photosynthesis. These substances do not have the same gelling or solidifying properties as agar.