Tissue level organization vs organ level organization

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Tissue-level organization Vs organ-level organization max. 4 The tissue level of organization occurs in Hydra. Cells are grouped in coherent masses for performance of one or more special functions e.g. musculo-epithelial tissue, nervous tissue . The tentacles may be given the status of organs , consisting of several types of tissues (musculo-epithelial cells, sensory cells, interstitial cells, nematoblasts, endoderm cells) coordinated for performance of one or more functions (food capture, conveyance of food to mouth, looping movements). Division of labours among cells lead to formation of organs specialised for more sophisticated functions in tapeworm and earthworm e.g. ovary and testis in tapeworm, nephridia in earthworm. In tapeworm, in adaptation to its parasitic mode of life, there is no alimentary canal. Digested food of the host is absorbed over whole surface. The nervous system is reduced . A very large number of proglottides are produced. The oldest proglottis is the most posterior . Every mature proglottis contains a full set of male and female reproductive organs . Acoelomate Vs coelomate max.4 Movements of body wall occur independently of peristaltic movements of gut wall and digestive processes. The coelom provides a large cavity in which organs can be developed and can perform their functions without interference from other organs. Location of these organs in coelom necessitates excretory and reproductive ducts to convey products to exterior. Coetomic fluid gives support , protection and assistance with locomotion . Development of coelom has necessitated a blood-vascular system for transport of digested food and oxygen. Proglottis Vs metamerism max. 2 The earthworm exhibits metameric segmentation. Typically every segment is exactly similar. Although the segments are partitioned from one another, they are coordinated and do not function as independent units . The main advantage of segmentation is that it provides an opportunity for specialization in certain segments without interference with others. In contrast to the proglottis of tapeworms, in earthworm there is a definite number of segments. There is no region capable of permanent proliferation of segments. The oldest segment is the most anterior.
The continuous proliferation of proglottids ,in tapeworm enhances the animals chance of survival due to production of large numbers of eggs.
Radial symmetry Vs bilateral symmetry max. 2 Any appropriate significance in relation to body symmetry. 'e.g. radial symmetry in relation to the sessile life of some coelenterates max.(20) Back to top HKALE 1995 Biology Paper I HKALE 1995 Biology Paper I Paper I Section A (*spelling mistakes of these terms, no mark) 1. prokaryotes eukaryotes no distinct nucleus / lack nuclear membrane distinct nucleus / with nuclear membrane 1 single circular DNA molecule in cytoplasm / no chromosome chromosomes present 1 lack membraneous organelles membraneous organelles present 1 infolding of the cell membrane forms mesosomes for respiration mitochondria for respiration 1 (4) Mark deduction : No table, minus 1

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