Useful actions of algae - class-VIII

• Gelidium and Gracilaria are also types of red algae. Agar, a commercial product is also obtained from these algae are used to growing microbes and in preparation of ice cream and jellies.
• Porphyra and Laminaria are some species of algae which are used as food.
• Algin a colloidal substance derived from marine brown algae and used as emulsifiers or thickeners. It is used in many foods, such as ice cream, jam, yogurt, and some other dairy products.
• Carrageenan is also used to thicken, emulsify and preserve foods and drinks. It comes from red algae. 
• So, the correct answer is " A - (ii), B- (iii), C - (i),  D - (iv) ".

Algae have great economic importance to man as it is a rich source of protein and some algae may be used as future food apart from this, it is also true that algae enriches the soil and can be a good source to make the soil fertile. Algae are being commercially used by man in many ways. Red algae is used to produce edible gelatin. Thus, the correct answer is option D.

Agar is a jelly-like substance, obtained from algae and discovered in the late 1650s or early 1660s. Agar is derived from the polysaccharide agarose, which forms the supporting structure in the cell walls of certain species of algae, and which is released on boiling. These algae are known as agarophytes and belong to the Rhodophyta (red algae) phylum. Agar is actually the resulting mixture of two components: the linear polysaccharide agarose, and a heterogeneous mixture of smaller molecules called agaropectin.The gelling agent in agar is an unbranched polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidium and Gracilaria. For commercial purposes, it is derived primarily from Gelidium amansii. In chemical terms, agar is a polymer made up of subunits of the sugar galactose.

Chlorella is an alga with extremely important health benefits. It contains nearly 50% of proteins. It also contains certain essential amino acids. But because of its hard cell wall, it cannot be digested easily. So, it is available in the form of food supplements as tablets, capsules etc.

The majority of blue-greens are aerobic photoautotrophs, their life processes require only oxygen, light and inorganic substances. At the onset of nitrogen limitation, during bloom conditions, certain cells in Anabaena evolve into heterocysts, which convert nitrogen gas into ammonium, which is then distributed to the neighboring cells of a filament. In addition, blue-greens that form symbiotic (mutually beneficial) relationships with a wide range of other life forms, can convert nitrogen gas into ammonium.

In addition to their ecological roles as oxygen producers and as the food base for almost all aquatic life, algae are economically important as a source of crude oil and as sources of food and a number of pharmaceutical and industrial products for humans. The taxonomy of algae is contentious and subject to rapid change as new molecular information is discovered. The study of algae is called phycology, and a person who studies algae is a phycologist.

Some dieters say that blue green algae helps satisfy appetite and supplies good nutrition while dieting. Some dieters say that bluegreen algae Spirulina, a well-known example, is a group of 1,500 species of microscopic aquatic plants. The two most common species used for human consumption are Spirulina maxima and Spirulina platensis. Spirulina is particularly rich in protein and also contains carotenoids, vitamins, minerals, and essential fatty acids. Blue-green algae (Spirulina) is a concentrated source of nutrients compared to most foods, but it is expensive compared to other supplemental sources of protein, vitamins, and minerals.

Algae is a collective term for all those chlorophyll bearing organisms which are thalloid. So, during photosynthesis by taking in ${CO _2}$ and giving out ${O _2}$ they purify the atmosphere

• All of the above organisms are the genus of cyanobacteria which are used for fixing nitrogen in the nitrogen cycle.
• So the correct answer is 'All of the above'.

Chlorella is widely known in biological studies for its efficiency in photosynthesis, making it a candidate for oxygen regeneration and food production in closed environments like space crafts.

Algae are primary producers that can be cultivated as a sustainable food source, which is a significant area of research for future human nutrition.

Unicellular algae chlorellin which contained in chlorella. 

Agar or agar-agar is a jelly-like substance, obtained from algae. The gelling agent in agar is an unbranched polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidium and Gracilaria. For commercial purposes, it is derived primarily from Gelidium amansii. In chemical terms, agar is a polymer made up of subunits of the sugar galactose.

Laminaria is a type of seaweed that is native to Japan. Laminaria contains iodine, an element that the body needs to make thyroid hormones. It is also a rich source of iron and potassium. Despite serious safety concerns about Laminaria, some people use Laminaria as medicine. Laminaria is used for weight loss, high blood pressure, as a bulk laxative for constipation, and for treating radiation sickness. It is also used for preventing cancer. Laminariales (kelps) are a major biogeochemical pump of iodine. "Laminaria" species of kelp is the species highest in iodine content. 

Synechocystis is a cyanobacterium (often grouped with algae in general contexts) known for its ability to produce tocopherol (Vitamin E).