Knowledge of Science

Pearl culture   Pearl fisheries-   pearl is a white highly shining globular concretion found within the shell of oyster.The natural pearls are rare due to the mode of formation. Scientist have succeeded in producing pearls of the same substance. This is known as the pearl fisheries. History of pearl industry-   The idea of pearl culture was evoked in Japan and was carried out at South coast of Hansoo in the Bay of Japan. Kokichi Mikimoto is said to be the father of pearl industry in Japan. Pearl producing Molluscs- High quality of pearls are obtained from Pinctada. A number of species of genus Pinctada like P. valgaris, P. chemnitzi, P. atropurpurea are pearl producing molluscs. All these species are marine. Pearl producing places in India- Natural habitat of pearl oysters are ridges of rocks or dead corals at a depth of 18-22 metres at a distance of 19 kilometres from the shore. The pearl oysters are obtained from the gulf of kutch , pak bay and Baroda. Pearl

  Economic importance of protozoa    The protozoans are harmful as well as beneficial. A large number of  them cause serious diseases in man, cattle poultry and fishes. Some of them are beneficial in the sense that they are helpful in sanitation, provide food, make oceanic ooze and heip in the study of various biological processes. Harmful Protozoa  Harmful protozoa are mainly parasitic which live either in or upon the body of other animals and causes diseases. 1) Parasites of Mouth-  Example- Entamoeba gingivalis, Lishmania brasiliensis 2) Parasites of digestive tract-  Example- Entamoeba histolytica, Giardia intestinalis 3)Parasites of blood and lymph-  Example- Trypanosoma gambiense, Leishmania donovani 4) Parasites of urinogenital duct- Example- Trichomonas vaginalis         B eneficial Protozoa 1) Helpful in Sanitation 2)Protozoa as food 3)Symbiotic Protozoa 4)Protozoa in study

        Phylum Protozoa (L.Proto-primitive , zoon- animals)  Diagnostic characters- 1) Microscopic 2)  Unicellular 3) Eukaryotic 4) Body divided into ectoplasm and endoplasm. 5) Terrestrial, aquatic, free living or parasitic. 6) Movement by cilia, flagella, pseudopodia etc. 7)  Nutrition performed by autotrophic or heterotrophic. 8)  protozoans are both harmful or beneficial. 9) All the biological activities are performed by different cell organelles. 10) Reproduction by asexual or sexual reproduction. Example- Amoeba, Paramecium, Euglena , Plasmodium etc.

              Phylum Porifera Natural history-   Sponges belonging to phylum Porifera (L.porus, pores+ ferre,to bear) are sessile organisms with a low degree of individuality and cellular organisation.sponges appear like plants being sessile and attached to rocks,shells and other solid objects. Most sponges are marine distributed from Arctic to tropical seas, living from the low tide line to depths of 6 kilometres.one family (spongillidae) is distributed in fresh water. Many sponges are drab coloured and others are brilliantly red, orange, yellow, violet, black and blue.The sponges have commercial importance being used in bathroom or in automobiles . Diagnostic characters-  1) Cellular grade of organisations. 2) Body bears several pores and hence the name Porifera. 3)Presence of canal system. 4) skeleton of calcareous or siliceous or horny spongin fibres. 5) commonly known as sponges. 6) asexual reproduction by gemmules and sexual reproduction by sperm and ova. Class

Nucleic Acids  The nucleic acid are the hereditary determinants of living beings. They are the macromolecules present in most living cells. Discovery -    It is discovered by Miescher in 1874 from the DNA-protamine complex in salmon sperm nuclei and named nuclein. Later it was found that the nuclein had acid properties and hence Altman in 1899 introduced the term nucleic acid to replace nuclein. In 1880 Fischer discovered purine and pyrimidine bases in nucleic acids. Types-   There are the two kinds of the nucleic acids 1) DNA(Deoxyribonucleic acid) 2)RNA(Ribonucleic acid) Both types of the nucleic acid are present in all plants and animals. Structural components of RNA and DNA-    1) Acid-   Phosphoric acid  2)Pentose sugar- Deoxyribose sugar and ribose sugar 3) Nitrogenous bases-   1) Purines (Adenine and Guanine)                                           2)   Pyrimidines (Cytosine, Thymine and Uracil) Nucleosides-   The nucleosides are the compounds in which

                                            PHYLUM -   MOLLUSCA                                                                      characters-                                                                                                                                 1)unsegmented                                                                                                                                2)presence of shell mantle,visceral mass and foot.                                                                      3)circulatory system open.                                                                                                             4)excretion by paired metanephridia.                                                                                                                                                                                                                                                     EXAMPLE- PILA, UNIO, OCTOPUS,DORIS etc.