Gelidium and Gracilaria are red algae used in industry. Which of the following commercial products obtained from these algae is widely used to grow microbes in laboratories and in preparations of ice creams and jellies?

Introduction / Context:
Many marine algae are important sources of industrial products used in food, microbiology and pharmaceuticals. Red algae such as Gelidium and Gracilaria are especially significant in this regard. This question asks which commercial product derived from these algae is used to grow microbes and in preparations of ice creams and jellies. Understanding this link between biology and industry is valuable in both biology and chemistry education.

Given Data / Assumptions:

• Gelidium and Gracilaria are species of red algae.
• They are processed to obtain a polysaccharide product.
• The product is used as a solidifying agent in microbiological media.
• The same product is also used in food as a gelling or stabilising agent.

Concept / Approach:
From red algae such as Gelidium and Gracilaria, a jelly like substance called agar is extracted. Agar is a mixture of polysaccharides that dissolve in hot water and form a firm gel on cooling. In microbiology laboratories, agar is used as a solidifying agent in culture media to grow bacteria and fungi. In the food industry, agar is used in desserts, jellies, and as a stabiliser in ice cream. Other options like Chlorella and Spirulina are microalgae used as protein rich food supplements, not as gelling agents, and gymnosperms are seed plants, not algae.

Step-by-Step Solution:

Verification / Alternative check:
Biology and biotechnology textbooks state that agar is obtained mainly from certain red algae such as Gelidium and Gracilaria. In every microbiology laboratory, agar plates and agar slants are standard tools for culturing microbes. Nutrient agar, MacConkey agar, and many other media rely on agar as the solidifying agent. Food science references also mention agar as a vegetarian substitute for gelatin in desserts and as a stabiliser in products like ice cream. These cross disciplinary references all point to agar as the correct commercial product derived from these red algae.

Why Other Options Are Wrong:

• Chlorella: A unicellular green alga used as a protein rich food supplement, not as a gelling agent.
• Spirulina: A filamentous cyanobacterium (blue green alga) also used as a health supplement, not used for agar production.
• Gymnosperms: A group of seed plants, including conifers, unrelated to marine red algae and not a commercial product.
• Alginates: These are extracted mainly from brown algae such as Laminaria and are used as thickening agents, not specifically as the product named in the question.

Common Pitfalls:
Students may confuse different algal products such as agar and alginates or may mix up the specific algae from which each is obtained. Another mistake is to focus only on food uses and ignore microbiological uses. A helpful approach is to remember that agar comes from red algae and is used to grow microbes, whereas alginates come from brown algae and are used to thicken products like toothpaste and ice cream. Chlorella and Spirulina are more associated with health foods and tablets.

Final Answer:
The commercial product obtained from Gelidium and Gracilaria and used to grow microbes and prepare jellies and ice creams is Agar.