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Excretory Products and Their Elimination: Solutions
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Important Notes on Excretory Products & Elimination
Types of Nephrons
- Juxtamedullary Nephron – About 15% of total nephrons, Glomeruli are found in inner region of cortex, large in size, long loop of Henle and found deep in medulla, associated with vasa recta control plasma volume when water supply is short.
- Cortical Nephron – About 85% of total nephron mainly lie in renal cortex, glomeruli found in outer cortex, short loop of Henle, extends very little in medulla. They do not have vasa recta.
- The animals which excrete ammonia are called ammonotelic and excretion of ammonia is known as ammonotelism e.g. Amoeba, sycon, hydra, liver fluke, tapeworm, Leech, Prawn, bony fishes etc.
- Ureotelism: Excretion of urea is known as ureotelism and the animals which excrete urea are ureotelic animals for example Mammals, many terrestrial amphibians and marine fishes and sting rays etc.
- Uricotelism: Excretion of uric-acid is known as uricotelism and the animals are called uricotelic for example most insects, land snails, lizards, snakes and birds.
- Nephrons: The structural and functional unit of kidneys. Each kidney contains about one million of nephrons.
- Structure of Nephron: A nephron consists of Glomerulus, Bowman’s capsule, PCT (Proximal convoluted tubule). JG A (Juxaglomerular Apparatus) and the collecting duct.
- Glomerular Filtration: The filtration of blood in glomerulus, about 1100-1200 ml of blood is filtered by the kidney per minute.
- Glomerular Filtration Rate (GFR): The amount of filtrate formed by the kidney per minute is called GFR. In a healthy individual it is about, 125 ml/minute, i.e. 180 litres per day.
Steps of Urine Formation
- Glomerular Filtration – Blood is filtered by glomerulus through three membranes i.e., endothelium of blood vessel, filtration slits of Bowman’s capsule and basement membrane between these two layers. This filtration is called ultrafiltration as all constituents of plasma comes into filtrate except proteins.
- Reabsorption – 90% of filtrate is reabsorbed by the renal tubules by active or passive mechanism. It is evident by the fact that out of 180L of filtrate formed per day only 1.5 L of urine released.
- Secretion – Tubular cells secrete H+, K+, ammonia into the urine. It maintains acid-base balance of body fluids.