SUMMARY
Division of labour is demonstrated by how cells, tissues, organs, and organ systems divide up the work in a way that assures the survival of the organism as a whole. A tissue is described as a collection of cells and intercellular molecules that carry out one or more bodily activities. Epithelia are tissue sheets that line the surface of the body as well as its cavities, ducts, and tubes. Epithelia have a single unoccupied surface that faces a bodily fluid or the environment. Junctions connect their cells physically and functionally. Various connective tissue types in the body link together, support, strengthen, protect, and insulate other tissue. Protein fibres and a variety of cells organised in a ground substance make up the soft connective tissues. Soft connective tissues consist of protein fibres as well as a variety of cells arranged in a ground substance. Cartilage, bone. blood, and adipose tissue are specialised connective tissues Cartilage and bone are both structural materials Blood is a fluid tissue with transport functions. Adipose tissue is a reservoir of stored energy. Muscle tissue, which can contract (shorten) in response to stimulation. helps in movement of the body and specific body parts. Skeletal muscle is the muscle tissue attached to bones Smooth muscle is a component of internal organs. Cardiac muscle makes up the contractile walls of the heart. Connective tissue covers all three types of tissues. Nervous tissue exerts greatest control over the response of body. Neurons are the basic units of nervous tissue. Soft connective tissues consist of protein fibres as well as a variety of cells arranged in a ground substance. Cartilage, bone. blood, and adipose tissue are specialised connective tissues Cartilage and bone are both structural materials Blood is a fluid tissue with transport functions. Adipose tissue is a reservoir of stored energy. Muscle tissue, which can contract (shorten) in response to stimulation. helps in movement of the body and specific body parts. Skeletal muscle is the muscle tissue attached to bones Smooth muscle is a component of internal organs. Cardiac muscle makes up the contractile walls of the heart. Connective tissue covers all three types of tissues. Nervous tissue exerts greatest control over the response of body. Neurons are the basic units of nervous tissue. Earthworm. Cockroach and Frog show characteristic features in body. organisation In Pheretima posthuma (earthworm), the body is covered by cuticle All segments of its body are alike except the 14, 15 and 16" segment, which are thick and dark and glandular forming clitellum. A ring of S-shaped chitinous setae is found in each segment. These setae help in locomotion. On the ventral side spermathecal openings are present in between the grooves of 5 and 6, 6 and 7,7 and 8 and 8 and 9 segments. Female genital pores are present on 14th segment. and male genital pores on 18" segment. The alimentary canal is a narrow tube made of mouth, buccal cavity, pharynx, gizzard, stomach, intestine and anus. The blood vascular system is of closed type with heart and valves. Nervous system is represented by ventral nerve cord. Earthworm is hermaphrodite. Two pairs of testes occur in the 10 and 11 segment, respectively. A pair of ovaries are present on 12 and 13 Intersegmental septum. It is a protandrous animal with cross- fertilisation. Fertilisation and development take place in cocoon secreted by the glands of clitellum. The body of Cockroach (Periplaneta americana) is covered by chitinous exoskeleton. It is divided into head. thorax and abdomen. Segments bear jointed appendages. There are three segments of thorax, each bearing a pair of walking legs. Two pairs of wings are present, one pair each on 2 and 3 segment. There are ten segments in abdomen. Alimentary canal is well developed with a mouth surrounded by mouth parts, a pharynx oesophagus, crop, gizzard, midgut hindgut and anus. Hepatic caecae are present at the junction of foregut and midgut. Malpighian tubules are present at the junction of midgut and hindgut and help in excretion. A pair of salivary gland is present near crop. The blood vascular system is of open type. Respiration takes place by network of tracheae. Trachea opens outside with spiracles. Nervous system is represented by segmentally arranged ganglia and ventral nerve cord. A pair of testes is present in 4-6 segments and ovaries in 26th segments. Fertilisation is internal. Female produces 9:10 ootheca bearing developing embryos. After rupturing of single ootheca sixteen young ones, called nymphs come out The Indian bullfrog. Rana tigrina, is the common frog found in India. Body in covered by skin. Mucous glands are present in the skin which is highly vascularised and helps in respiration in water and on land. Body is divisible into head and trunk. A muscular tongue is present, which is bilobed at the tip and is used in capturing the prey. Nervous system is organised into central, peripheral and autonomic. The organs of urinogenital system are kidneys and urinogenital ducts, which open into the cloaca. The male reproductive organ is a pair of testes. The female reproductive organ is a pair of ovaries. A female lays 2500 3000 ova at a time. The fertilisation and development are external. The eggs hatch into tadpoles, which metamorphose into frogs.
