11th Class

Chloroplast (The site of photosynthesis) : Chloroplast are green plastids which function as the site of photosynthesis in eukaryotic photoautotrops. Photosynthetic unit can be defined as number of pigment molecules required to affect a photochemical act, that is the release of a molecule of oxygen. Park and Biggins (1964) gave the term quantasome for photosynthetic units is equivalent to 230 chlorophyll molecules. Chloroplast pigments : Pigments are the organic molecules that absorb light of specific wavelengths in the visible region due to presence of conjugated double bonds in their structures. The chloroplast pigments are fat soluble and are located in the lipid part of the thylakoid membranes. There is a wide range of chloroplastic pigments which constitute more than 5% of the total dry weight of the chloroplast. They are grouped under two main categories : (1) Chlorophylls : Chlorophyll 'a' is found in all the oxygen evolving photosynthetic plants more...

  Class 1. Chondrichthyes (The Cartilaginous Fishes) (Gk. chondros = cartilage; ichthys = fish) General characters. (1) Mostly marine and predaceous. (2) Body fusiform or spindle shaped. (3) Fins both median and paired, all supported by fin rays. Pelvic fins bear claspers in male. Tail heterocercal. (4) Skin tough containing minute placoid scales and mucous glands. (5) Endoskeleton entirely cartilaginous, without true bones. Notochord persistent. Vertebrae complete and separate. Pectoral and pelvic girdles present. (6) Mouth ventral. Jaws present. Teeth are modified placoid scales. Stomach J-shaped. Intestine with spiral valve. (7) Respiration by 5 to 7 pairs of gills. Gill-slits separate and uncovered (except, chimaeras). Operculum absent. No air bladder and lungs. (8) Heart 2–chambered (1 auricle and 1 ventricle). Sinus venosus and conus arteriosus present. Both renal and portal systems present. Temperature variable (poikilothermous or more...

(Gk. platys = broad or flat; helmin = worm) Brief History : Aristotle mentioned tapeworms, but scientific studies of flatworms began only in the 18th century. It was Gegenbaur (1859) who placed these in a separate group and suggested the present name of the phylum. General Characters (1) They are dorso-ventrally flattened like a leaf. (2) They show organ grade of organization. (3) They are acoelomate animals. The cavity in platyhelminthes is filled with mesenchyme or parenchyma. (4) They are triploblastic animals. The cells of the body wall are arranged in three layers.They are the ectoderm, the mesoderm and the endoderm. (5) They are bilaterally symmetrical animals. The body of the animal can be divided into two equal similar halves through only one plan. Animals with this symmetry have definite polarity of anterior and posterior ends. (6) Some members have segmented body. The segmentation in platyhelminthes is called pseudometamerism. (7) more...

(Gk. Porus = Pore; ferre = To bear) Brief History : Robert Grant (1825) finally proved that sponges are animals, and coined the name ‘Porifera’ for these. Schulze (1878), Butschli (1884), Sollas (1884) and Delage (1898) separated sponges from other metazoans on the basis of embryological studies, and suggested a separate group, “Parazoa” for these. General Characters   (1) All the sponges are aquatic, sedentary, asymmetrical or radially symmetrical. First multicellular organisms and have cellular grade of organization. (2) They are diploblastic. Ectoderm is formed by pinachocyte and endoderm is formed by choanocyte. Both layers are called pinachoderm and choanoderm. A gelatinous noncellular mesenchyme present in between them. (3) Mesenchyme contains free amoebocytes and skeletal elements. (4) Different types of amoebocytes are : Archaeocytes                :   undifferentiated totipotent cells. Chromocytes                 :   with pigment granules. Thesocytes                     :   with reserve more...

(1) Hydra belongs to class Hydrozoa of phylum coelenterata. (2) Trembly (1744), a Swiss biologist discovered Hydra. Linnaeus (1758) gave the name Hydra, a Greek word, means ‘Water serpent’ based on its ability to regenerate its lost parts. (3) Hydra is a solitary polyp found in freshwater (stagnant). Among coelenterates Hydra is one of the smallest polyps. (4) It is colourless carnivorous coelenterate having radial symmetry. (5) Hydra is a diploblastic and has tissue grade of organization with division of labour on morphological basis. (6) Chlorohydra viridissima is called green hydra. It is green because of symbiotic association with a unicellular green algae Chlorella vulgaris. Algae live in the musculonutritive cells of Hydra. (7) Hydra has a cylindrical body with 6-10 hollow tentacles. It help in locomotion and food capture, so analogous (correspond functionally) to pseudopodia of Amoeba. (8) Mouth is situated more...

(1) Dugesia (Planaria) is found commonly in freshwater ponds, lakes, streams and shallow rivers. (2) Planaria are gregarious, i.e., they live in groups. (3) The head bears a pair of lateral projections called auricles. (4) The mouth opens on the mid ventral surface near the middle of the animal. (5) The pharynx is a tubular structure that can be everted beyond the mouth. (6) Planarians have remarkable power of regeneration. (7) If an individual is cut transversely into two parts, the anterior fragment will regenerate a new tail and a posterior piece will develop a new head. (8) Neoblast cells found in planarians which is help in regeneration.         (1) Fasciola hepatica, commonly known as sheep liver fluke is an endoparasite of sheep more...

(1) Ascaris lumbricoides, the common roundworm belong to the class Rhabditea of the phylum Nemathelminthes. It is the most common endoparasite in the small intestine of human beings. It is monogenetic, i.e., without any secondary host. The worm is more common in children. (2) The body is elongated, unsegmented, cylindrical with tapering ends and four streaks-two lateral, one ventral and one dorsal. (3) Sexes are separate with sexual dimorphism. Male is smaller than female with curved tail, two penial setae (copulatory organs) and cloaca. Female is with straight posterior end of the body and posterior transverse anus and separate gonopore situated ventrally 1/3 from the anterior end. In both the excretory pore is situated mid-ventrally, a little behind the mouth. Ventral surface of male bears fifty pairs preanal and five pairs postanal papillae. These more...

(1) The common Indian earthworm, Pheretima posthuma belong to the class oligochaeta of the phylum Annelida. It is found in every part of the world. It lives in damp soil and burrow in lawns, fields, garden etc. rich in humus. Earthworm is nocturnal i.e., active during night. (2) The generic name Pheretima was first used by Kinberg in 1867. Our knowleage of Pheretima is mainly due to the work of Karm Narayan Bahl (1926). (3) Body is cylindrical, bilaterally symmetrical, elongated with metameric segmentation. Earthworm shows both external and internal segmentation. The number of segments is about 100-120, the length is about 150 mm.     (4) Earthworm is brown or clay-coloured. This is because of the pigment porphyrin. Numerous granules of more...

(1) Cockroach belong to the class insecta of the phylum Arthropoda. (2) Two species of cockroaches commonly found in India are? Periplaneta americana and Blatta orientalis. Periplaneta americana is the largest and most common species. The generic name periplaneta was given by Burmeister in 1838. (3) Cockroaches are nocternal and cursorial (running). It is cosmopolitan in distribution, but cockroach are more abundant in warm, humid areas. (4) Body is divided into head, thorax and abdomen. Head is derived by the fusion of six embryonic segments. The part of head between and behind the eyes is epicranium (vertex). The front of head capsule is made up of three unpaired flattened sclerites called frons, clypeus and labrum. (5) The thorax consists of three segments-prothorax, mesothorax and metathorax. Thorax bears three pairs of jointed appendages and two pairs of more...

References of classification of organisms are available in Upanishads and Vedas (1500 B.C. to 600 B.C.). However, earliest human activity can be traced back to early, middle and late stone age (400,000 B.C. – 200,000 B.C.). About 740 plants and 250 animals have been mentioned in Vedic literature. Few significant references in old literature are, (1) Chandyogya Upanishad : Here the animals have been classified into three categories – (i) Jiraja (Viviparous) e.g. mammals. (ii) Andaja (Oviparous) e.g. birds, reptiles, insects and   worms. (iii) Ubhija (Vegetal origin) e.g. small animals. (2) Susruta Samhita (600 B.C.) : Here organisms were classified into, (i) Sthavara in which immobile organisms like plants were kept. (ii) Jangama in which mobile organisms like animals were placed.