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WHAT ARE THE EVIDENCES FOR EVOLUTION? NEET (part-1)

7.3 WHAT ARE THE EVIDENCES FOR EVOLUTION? Evidence that evolution of life forms has indeed taken place on earth has come from many quarters.  Paleontological evidence . Fossils are remains of hard parts of life-forms found in rocks.  father of Indian paleontology- Birbal Sahani Rocks form sediments and a cross-section of earth's crust indicates the arrangement of sediments one over the other during the long history of earth.  Different-aged rock sediments contain fossils of different life-forms who probably died during the formation of the particular sediment.  Some of them appear similar to modern organisms.  They represent extinct organisms (e.g., Dinosaurs).  Birds  are the only surviving  dinosaurs . A study of fossils in different sedimentary layers indicates the geological period in which they existed.  The study showed that life-forms varied over time and c...
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Nephron Vs Nephridium (Meta-nephidia & Proto-nephridia)

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  Nephrons  Each kidney has nearly one million complex tubular structures called nephrons (Figure 19.3), which are the functional units. Each nephron has two parts – the glomerulus and the renal tubule. Glomerulus is a tuft of capillaries formed bythe afferent arteriole – a fine branch of renal artery. Blood from the glomerulus is carried away by an efferent arteriole   The nephridium (plural nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidney. Nephridia remove metabolic wastes from an animal's body. In addition to two basic categories ( metanephridia and protonephridia ), other types may exist. Metanephridia A metanephridium (meta = "after") is a type of excretory gland found in many types of invertebrates such as annelids, arthropods and mollusca. (In mollusca, it is known as the Bojanus organ.) A metanephridium typically consists of a ciliated funnel opening into the body cavity, or coelom connected to a duct...
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DIGESTION AND ABSORPTION

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DIGESTION AND ABSORPTION Food is one of the basic requirements of all living organisms.  The major components of our food are carbohydrates, proteins and fats.  Vitamins and minerals are also required in small quantities.  Food provides energy and organic materials for growth and repair of tissues.  The water we take in, plays an important role in metabolic processes and also prevents dehydration of the body.  Biomacromolecules in food cannot be utilised by our body in their original form. They have to be broken down and converted into simple substances in the digestive system.  This process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical methods.  General organisation of the human digestive system is shown in Figure 16.1. 16.1 DIGESTIVE SYSTEM  The human digestive system consists of the alimentary canal and the a...
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