Agar-agar is made from marine red algae (Gelidium, Gracilaria, Gigartina). It is used in the preparation of several types of food.

(i) Alum, glass, soda, potash, alginic acid and soap are made from seaweed kelp.
(ii) Ice-creams, jellies, paints, varnishes, shampoos and cosmetics are made from olgin of brown algae and gelatin of red algae.
(iii) Soap, paper, photography, rayon etc. are made from algae agar.
(iv) Polymers like starch and polyhydroxy-alkanoates are formed naturally in algae. Bioplastics are made from all these polymers.
(v) Carrageenan from algae (Chondrus crispus) is used in food processing, rayon, pharmaceutical industry, leather industry, toothpaste and dyes.
(vi) Algae (Furcellaria) furcellaran is used in making jam-jelly, preserving fish and meat and in toothpaste and pharmaceutical industry.
(vii) Algae (Gleopeltis furcata) is used in pulp and paper industry and for making glue.
(viii) Iodine and potash are produced from Laminaria algae.

Chlorella is used in space research to purify the polluted air of spacecraft. Chlorella fulfills the oxygen demand in space.

Agar agar is made from Gelidium, Gracilaria, Pterocladia etc., Goiter medicine is made from Sargassum and Laminaria and Chloreline antibiotic is made from Chlorella. Galactans are produced from the red algae Callophyllis variegate and Agardhiella tenera. Galactans are used to prevent HIV. Oral cancer drugs are made from algae containing beta-carotene, which has antioxidant properties.

Diatomaceous (Navicula) algae bodies accumulate at the bottom of water bodies to form diatomaceous earth or diatomite. Soil age is determined by carbon dating the shells of diatoms deposited in the soil layer. Diatomite is used to make water filters, boilers, blast furnaces, metal polishes, toothpastes, etc. Diatomaceous earth was used to make dynamite.

Seaweed is used as a source of potash fertilizer. Such as Spirulina, Scytonema, Oscillatoria, Anabaena, Nostoc etc.
10. Determining the location of spy submarines: Blue-green algae contain pigment particles called phycobilin protein. These pigment particles (C-phycoerythrin, C-phycocyanin) absorb the diffracted rays from spy submarines. The location of the spy submarine is determined by the amount of absorbed radiation.

Biofuel or Biodiesel is made from algae. So algae are called second generation biofuels. Botryococcus braunii algae is being used to make biofuel. Attempts are being made to produce biofuel from Chlorella and Scenedesmus algae. Recently, researchers are trying to produce third generation biofuels from microalgal biomass. Some micro-algal species Kirchneriella lunaris, Ankistrodesmus fusiformis, Ankistrodesmus falcatus, Chlamydocapsa bacillus, Chlorella, Scenedesmus etc. have been taken for biodiesel production.

Areas of the sea where there is a large amount of algae are found to have a large number of fish. The location of the fish is determined by satellite. As a result, a large amount of fish can be caught in a short time.

Algae produce oxygen and absorb carbon dioxide. As a result, the purity of the atmosphere is preserved. Algae is used to treat sewage. Nitzschia (diatom) algae are used in water purification. Chlorella algae are used in air purification and sewage removal. As a result, environmental pollution is prevented.

Algae produce oxygen in the process of photosynthesis. Algae produce 60% of Earth’s oxygen.