Title EXCRETORY PRODUCTS & THEIR ELIMINATION.pdf ✅

 Digital Pvt. Ltd. www.allendigital.in [ 127 ] 1. Introduction : • Animals accumulate ammonia, urea, uric acid, carbon dioxide, water and ions like Na+, K+, Cl–, phosphate, sulphate, etc., either by metabolic activities or by other means like excess ingestion. These substances have to be removed totally or partially. • Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by the animals. Ammonia is the most toxic form and requires large amount of water for its elimination, whereas uric acid, being the least toxic, can be removed with a minimum loss of water. • The process of excreting ammonia is Ammonotelism. Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic in nature. Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions. Kidneys do not play any significant role in its removal. • Terrestrial adaptation necessitates the production of lesser toxic nitrogenous wastes like urea and uric acid for conservation of water. Mammals, many terrestrial amphibians and marine fishes mainly excrete urea are called ureotelic animals. Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood which is filtered and excreted out by the kidneys. Some amount of urea may be retained in the kidney matrix of some of these animals to maintain a desired osmolarity. Characters Type of animals Excretory matter Ammonotelic Ureotelic Uricotelic Ammonia Urea Uric acid Requirement of water for removal of waste Very large Less than ammonia Least Toxicity Highest Less than ammonia Least Examples Aquatic insects Aquatic amphibia (Tadpoles) Mammals, marine fishes, Terrestrial amphibia (frog) Birds, Insects, Land Snails, many reptiles Excretory Products and their 03 Elimination
NEET : Biology [ 128 ] www.allendigital.in  Digital • Reptiles, birds, land snails and insects excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water and are called uricotelic animals. Ammonotelic Ureotelic Uricotelic Mechanism of excretion produced in the form of By diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions. by metabolism ammonia is converted into urea in the liver and released into the blood which is filtered and excreted out by the kidneys. Uric acid in the form of Paste or pellet Earthworms excrete ammonia when sufficient water is available while they excrete urea instead of ammonia in terrestrial environment. Excretion: Removal of mainly nitrogenous substances from the body which are end product of metabolic activity. OR The process which is concerned with removal of nitrogenous waste materials (e.g., urea, uric acid, CO2, ammonia, salts, excess water etc.) is termed excretion. Homeostasis : Maintenance of steady state (Walter Cannon). Homeostatic mechanism is important for normal life as they maintain condition within a range in which, the animal’s metabolic processes can occur. Ornithine Cycle : Ammonia is converted into urea in the liver. Its also called urea cycle. Excretory Organs in Animals : Excretory organs Protonephridia (Flame cells) Nephridia Malpighian tubules Green glands or Antennal glands Kidneys Examples – Platyhelminthes/ Flatworms (Planaria) – Rotifers – Some annelids – Cephalochordate (Amphioxus) – Annelids (Earthworms) – Most of the insects (Cockroaches) Crustaceans (Prawn) All vertebrates Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e. osmoregulation. 2NH3 + CO2 (Ammonia) NH2CONH2 + H2O (Urea) Most of invertebrates = Simple tubular form Vertebrates = Complex tubular organs called kidneys
Excretory Products and their Elimination  Digital www.allendigital.in [ 129 ] 1. "Homeostasis" term was proposed by - (1) Claude Bernard (2) Walter Cannon (3) Marcello Malpighi (4) Henle 2. Excretion in the from of uric acid and urates in birds is helpful in (1) Conserving body heat (2) Eliminating excess water (3) Conserving body water (4) Eliminating body water 3. Which one of following is the simplest excretory organs ? (1) Alveoli (2) Flame cells (3) Nephridia (4) Kidney 4. In comparison to urea ammonia is (1) Less toxic (2) Toxic (3) Highly toxic (4) None 5. Which excretory material is least toxic ? (1) Ammonia (2) Urea (3) Uric acid (4) All are equally toxic 6. Uric acid is nitrogenous waste in (1) Mammals and molluscs (2) Birds and lizards (3) Frog and cartilaginous fishes (4) Insects and bony fishes 7. (a) The conversion of a protein waste, the ammonia into urea, occurs in (b) Urea is synthesised in (1) Kidneys (2) Lungs (3) Intestine (4) Liver 8. Animals accumulates waste like urea, uric acid, CO2, H2O, ions like Na+, K+, Cl–, phosphate, sulphate, etc. by- (1) Metabolic activities (2) Excess ingestion (3) Either 1 or 2 (4) Excretion 9. Order of toxicity among ammonia, urea and uric acid (from lower to higher) is - (1) Uric acid < urea < ammonia (2) Uric acid < ammonia < urea (3) Urea < uric acid < ammonia (4) Ammonia < urea < uric acid 10. Match the following columns – Column I Column II A. Ammonotelic 1 Aquatic invertebrates B. Ureotelic 2 Reptiles C. Uricotelic 3 Birds 4 Amphibians 5 Mammals (1) A-4, 5 ; B-3 ; C-1, 2 (2) A-1, 2 ; B-3 ; C-4, 5 (3) A-1 ; B-4, 5 ; C-2, 3 (4) A-2, 3 ; B-1 ; C-4, 5 11. Among ammonia, uric acid and urea, which one needs the least amount of water to excrete - (1) Ammonia (2) Uric acid (3) Urea (4) Both 2 and 3 12. Ammonia produced by metabolism is converted into the ...A... in the ...B... in ureotelic and released into the blood, which is filtered and excreted out by ...C... (1) A-Uric acid, B-Spleen, C-Kidney (2) A-Uric acid, B-Liver, C-Kidney (3) A-Urea, B-Liver, C-Kidney (4) A-Urea, B-Spleen, C-Kidney 13. Match the following columns. Column I (Organisms) Column II (Excretory structures) A Annelids 1 Simple tubular forms B Platyhelminthes and rotifers 2 Complex tubular forms (Kidneys) C Vertebrates 3 Protonephridia or flame cells D Most invertebrates 4 Nephridia (1) A-1 ; B-2 ; C-3 ; D-4 (2) A-4 ; B-3 ; C-1 ; D-2 (3) A-1 ; B-2 ; C-4 ; D-3 (4) A-4 ; B-3 ; C-2 ; D-1 BEGINNER’S BOX-1 INTRODUCTION AND EXCRETORY ORGAN
NEET : Biology [ 130 ] www.allendigital.in  Digital 2. Human Excretory System : Human excretory system consists of : 1. A pair of kidneys. 2. A pair of ureters. 3. A urinary bladder 4. A urethra (A) Location of Kidneys :  Mammalian kidneys are bean shaped; reddish brown coloured with a tough fibrous connective tissue covering called renal capsule.  Kidneys are located laterally on either side of vertebral column levels between the last thoracic (T12) and third lumbar (L3) vertebra close to the dorsal inner wall of the abdominal cavity.  In humans, right kidney is at slightly lower level than left kidney, because of presence of liver in the right side of abdominal cavity. Each kidney measures 10-12 cm in length, 5-7 cm in width and 2-3 cm in thickness, weighing about 120-170 gm in an adult. Lateral surfaces of kidney are convex while medial surfaces are concave  Towards the centre of the inner concave surface of the kidney is a notch called Hilum (Hilus renalis). Through this, renal artery and nerve enter while renal vein and ureter leave the kidney.  Inner to the hilum is a broad funnel shaped space called the renal pelvis. (One pair) Kidney Ureter (One pair) Urinary bladder Urethra Medulla Cortex Pelvis Inferior vena cava Dorsal aorta Renal vein Renal artery C O N V E X C O N C A V E Hilum Renal artery Renal vein Renal pelvis Ureter Length 10-12 cm Thickness 2-3 cm Width 5-7 cm T12 L3