Lower metazoa-pattern of feeding and digestion in porifera and coelentrata notes & explanation MSC .

PATTERNS OF FEEDING AND DIGESTION IN LOWER INVERTEBRATES All living organisms require the presence of energy to do various activities of life. They get this energy from the nutrient they ingest. The nutrient is also needed for the growth and development of the body. The nutrition refers to sum total of all the processes concerned in the conversion of nutrients into the body stuffs to supply energy for various metabolic activities. The nutrition involves ingestion, digestion, absorption, assimilation and egestion (defaecation). The digestion includes conversion of non-diffusible foods into diffusible foods with the help of digestive enzymes. The animals having tissues/organs grade body organization, no pores in the body wall and obvious mouth and digestive cavity are grouped as metazoan. On the basis of differentiation of germ layer and formation of coelom, metazoans are grouped as: (1) Porifera (2) Coelenterata (3) Ctenophora (4) Platyhelminthes (5) Nematode (6) Nemertinea (7) Entoprocta (8) Acanthocephala (9) Gastrotricha (10) Nematomorpha and (11) Rotifera FEEDING AND DIGESTION IN PORIFERA Sycon (=Scypha) is a filter feeder. It shows intracellular digestion. Food of Scypha includes bacteria, protozoans, diatoms and minute organic particles and dead organic matter present in the water. In radial canal these get attached to the outer surface of collar of choanocytes and slowly drawn in the cytoplasm forming a food vacuole. The medium of food vacuole is first of all acidic and then it becomes alkaline. Digested food containing trypsin, pepsin, rennin,erepsin, lipase, amylase, invertase are secreted from choanocytes and poured into the food vacuoles. Food may be incompletely digested in choanocytes and then passed in to the wandering amoebocytes. These amoebocytes carry digested food from one cell to other cell. Phagocytosis occurs by pinnacocytes and porocytes. In other sponges, the food as it passes through incurrent canals goes to amoebocytes directly. The digested food is stores there as glycogen, fat and glycoprotein. FEEDING AND DIGESTION IN COELENTERATA The coelenterates are radially or biradially symmetrical tentacles bearing metazoan without head, organ or system. They are diploblastic and possess nematocysts, enteron (=gastrovascular cavity), opening by the mouth. The enteron may be simple sac like, branched or divided by septa. Digestion is both intrecellualr and intracellular. Obelia exhibits metagenesis with dominant poylp and medusa stages. These stages differ structurally and functionally. Nutrition in polyp stage: Polyp (=hydranth, gastrozoid or feeding stage) is chiefly carnivorous feeding on crustaceans, nematodes, worms etc. The prey is seized and taken to mouth with the help of 24 solid tentacles arranged in a circle around the base of hypostome. The tentacles are armed with nematocytes. The garstrodermal cells secrete digestive juices which disintegrate the food. The enzymes are proteolytic enzymes, succinic dehydrogenase, DPNH diphorase, TPNH diphorase, esterase, acid phosphatase, alkaline phosphatase, ATPase, Gluocse-6- phosphatase etc. Now these foods are transferred to amoeboid cells where intracellular digestion occurs. In the presence of proteolytic enzymes, digestion of protein occurs in coelenterons. Now pseudopodia are emerged from broader parts of muscular cells by which semi digested foods come in contact of food vacuole by phagocytosis. The medium of food vacuole is firstly acidic and then becomes alkaline in which digestion is completed except the digestion of starch. Nutrition in medusa stage: Obelia has an alimentary canal of mouth, gullet, stomach, radial canal and circular canal. Prey, feeding processes and digestion resemble these of polyp. However, prey is digested exclusively in the stomach. Sometimes, tentacular cells also ingest food particles. FEEDING AND DIGESTION IN CTENOPHORA The ctenophores are planktonic carnivorous. Their processes roughly resemble coelenterates. The food is captured either by rapping in a mucous sheet on the collobalsts of extended tentacles or moved into the mouth by ciliary action or simply by ingesting thorough open mouth while swimming with oral end foremost. Digestion begins extracellularly in pharynx and completed intracellularly in the gastrovascular canals. The ciliated portion helps in circulating the food into the canals o the canals. More details notes link :- http://maharajacollege.ac.in/fileuplo... Thanks Please subscribe