Urea Cycle Living organisms excrete the excess nitrogen resulting from the metabolic breakdown of amino acids in one of three ways. Many aquatic animals simply excrete ammonia. Where water is less, plentiful processes have evolved that convert ammonia to less toxic waste products which require less water for excretion. One such product is urea, which is excreted by most terrestrial vertebrates; another is uric acid, which is excreted by birds and terrestrial reptiles. Accordingly, living organisms are classified as being either ammonotelic (ammonia excreting), urotelic (urea excreting) and uricotelic (uric acid excreting). Some animals can shift from ammonotelism to urotelism or uricotelism if their water supply becomes restricted. Urea is synthesised in the liver by the enzymes of the urea cycle. It is then secreted into the blood stream and sequestered by the kidneys for excretion in the urine.The urea cycle reactions were elucidated by Hans Krebs and Kurt Henseleit. Thi...
LIVING CELL Introduction The cell is the basic structural and functional unit in all living organisms. Living forms vary in size but they are all made up of cells. In unicellular organisms, the cell is the organ. As an organism grow in complexity, the cells increase in number and similar cells aggregate into tissues and organs with specialized functions. The shape of the cell is often determined by its function and the size of the cell is determined by the optimum dimensions that will enable it to perform its duties more effectively . The human body is composed of a multiple of specialized tissues which inturn consist of vast clusters of cells differentiated into specialised chemical factories which perform various biochemical reactions. Types of cells Two general types are recognised in nature. They are prokaryotic and eukaryotic cells. Prokaryotic cells Prokaryotes were the first cells to arise in biological evolution. They are very small and simple having only a single membran...
Buffers of blood The important buffers present in blood are · Bicarbonate buffer · Phosphate buffer · Protein buffer · Hemoglobin buffer Bicarbonate buffer It is the most important buffer in blood plasma and consist of bicarbonate [HCO 3 -] and carbonic acid [H 2 CO 3 ] This buffer is efficient in maintaining the pH of blood plasma to 7.4 against the acids produced in tissue metabolism (eg) phosphoric acid, lactic acid, aceto acetic acid and b -hydroxy butyric acid. These acids are converted to their anions and the bicarbonate is converted to carbonic acid a weak acid. CO 2 thus formed is expirated through lungs during respiration. Phosphate buffer The phosphate buffer consists of dibasic phosphate...
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