Biology Past Paper 2024 - Excretion in Animals - PDF

Kuala Lumpur, Malaysia SEMESTER-1 NAME: _______________________ REF: 2024-25/ SCI /STD 10/ HO 05 CLASS: _______________ SUBJECT: Biology DATE: 29/05/2024...

Kuala Lumpur, Malaysia SEMESTER-1 NAME: _______________________ REF: 2024-25/ SCI /STD 10/ HO 05 CLASS: _______________ SUBJECT: Biology DATE: 29/05/2024 Topic: Excretion in Animals Excretion Excretion is the biological process of removing harmful metabolic wastes such as urea, uric acid (nitrogenous wastes) and salts from the body. Excretion in different kinds of organisms Unicellular organisms, like amoeba, remove wastes by simple diffusion from the body surface into the surrounding water. Surplus water in Amoeba is sent out through contractile vacuole. Lower multi-cellular organisms like flat worms use flame cells while earthworms use nephridia for excretion. In insects, a system involving Malpighian tubules is used to excrete metabolic waste. Aquatic amphibians eliminate nitrogenous waste across the skin in the form of ammonia, as ammonia is highly soluble in water. Higher multi-cellular organisms like fish, frogs when on land, lizards, birds and humans use kidneys for excretion. Animals are classified based on the nitrogenous waste excreted. The process of eliminating ammonia from the body is known as ammonotelism, and the organisms which exhibit this nature are called ammonotelic. For example, protozoans, echinoderms, poriferans, crustaceans, amphibians and bony fishes. Aquatic animals excrete ammonia directly into the environment; where the compound is quickly diluted. It is also very toxic to tissues. In some animals, urea is excreted as a metabolic waste product. Such organisms are called ureotelic. In these organisms, ammonia that is produced is converted to urea in the liver of these animals and is released back into the blood. The kidneys filter the urea and expel the urea outside the body. Some of the urea is retained in the matrix of the kidney to maintain a desired osmolarity in the organisms. Moreover, urea is comparatively less toxic than ammonia. For example, sharks, alligators, other mammals and man. Page 1 of 9 Copyright © Global Indian International School  Uricotelic animals remove nitrogenous wastes as uric acid in the form of pellets or paste. Metabolically, this process is quite costly; however, the water loss is minimal, and uric acid is the least toxic. Moreover, since uric acid is not readily soluble in water, the excrements form pasty white suspensions. Most reptiles, birds, and insects are classified as uricotelic. Note: Osmolarity is the total solute concentration within a specific volume of a solvent expressed in osmoles per liter (Osm/L) or milliosmoles per liter (mOsm/L). Human Excretory System As a result of various metabolic process going on in our body a number of waste products are formed. These have to be eliminated as they are toxic to the body. The waste products include: (i) Carbon dioxide which is liberated during respiration; and is eliminated by the lungs. (ii) Nitrogenous metabolic wastes, such as urea and uric acid produced in the liver from excessive consumption of proteins and is eliminated by the kidneys. (iii) Bile pigments: Bile pigments (e.g., bilirubin) derived by the breaking down of haemoglobin of the erythrocyte. (iv) Excess salts, water and water-soluble vitamins: They are eliminated by the kidneys. (v) Sweat contains 99% water, traces of urea and uric acid. However, after heavy exercise, lactic acid forms a major constituent of sweat. Sweat glands in the skin allow evaporation of excess water along with some salts which have to be excreted out of the body. Sweating is a vital function of your body. Sweating helps in thermoregulation of the body. The excretory system in human beings includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. This is also known as the urinary system Page 2 of 9 Copyright © Global Indian International School Kidneys: A pair of reddish brown, bean shaped structures located in the abdomen, one on either side of backbone. The right kidney is placed slightly lower than the left kidney as the right kidney is pushed down by the large liver. In a longitudinal section kidney comprises of two regions, outer region called renal cortex and inner region called renal medulla. The cortex has a random arrangement of tiny tubules called nephrons. Each kidney has 1.25 million nephrons; they are the functional unit of the kidney. The hilum is the concave part of the bean-shaped kidney, where blood vessels and nerves enter and exit the kidney; it is also the point of exit for the ureters. Kidney plays a vital role in the maintenance of homeostasis of our body by:  Excretion of nitrogenous waste products.  Regulation of water balance.  Regulation of acid base balance.  Elimination of other substances like drugs and pigments.  Regulation of blood pressure by secreting hormones. Note: Homeostasis is the state of steady internal chemical and physical conditions maintained by living systems. Ureters: The ureters are a pair of long narrow tubes that extend from the kidney to the urinary bladder. The upper end of the ureter enters the kidney and forms the funnel shaped basin called renal pelvis, the lower end enters the urinary bladder. Each ureter opens into the urinary bladder by an aperture. Valves at the openings of the ureter prevent the back flow of urine during contraction of the urinary bladder. Ureters transport urine from the kidneys to the urinary bladder. Urinary Bladder: This is a muscular sac like structure which temporarily stores urine. It can hold 0.5 to 1 litre of urine. It is situated in the lower end of the abdomen. The opening of the bladder into the urethra is guarded by sphincter muscles which remain closed till the time of urination. Urethra: It is a short muscular tube which arises from the neck of the urinary bladder and leads to the outside. In females it opens directly to the outside, in males it opens into the penis. In female urethra serves as passage way for urine only, in males both Page 3 of 9 Copyright © Global Indian International School urine and semen pass through the urethra. The opening of the urethra is also guarded by a ring of sphincter muscle. It relaxes during urination. Blood supply to the kidneys: Renal artery is a branch of the Aorta which enters the kidney at the hilum. It brings with it oxygenated blood containing nitrogenous waste. On entering the kidney, the renal artery divides repeatedly to form thin vessels called afferent arterioles. An afferent arteriole enters each Bowman’s capsule and breaks up into a network of capillaries which form a mass of capillaries called glomerulus. These capillaries unite to form an efferent arteriole. The efferent arteriole after emerging from the Bowman’s’ capsule runs a short distance and breaks up into a capillary network (vasa recta) which surrounds the renal tubule. The capillaries join to form renal venules, the renal venules unite to form renal vein which drains into the inferior vena cava. Nephron: It the basic structural and functional unit of the kidney. They are the microscopic structure composed of a renal corpuscle and a renal tubule. Structure of the Nephron: The Renal Corpuscle lies in the cortex of kidney and consists of a glomerulus surrounded by a Bowman’s capsule. Bowman’s capsule: Is a thin double walled cup like structure, its hollow internal space continues into the tubules. The cup-shaped capsule contains a network of capillaries called Glomerulus. It collects the incoming fluid from the glomerular capillaries. Page 4 of 9 Copyright © Global Indian International School Glomerulus: is a network of capillaries present inside the Bowman’s capsule. It is formed by the incoming capillaries of the afferent arteriole and that of the outgoing efferent arteriole. Renal tubule: The Bowman’s capsule leads to a highly coiled part of nephron called renal tubule. It is further differentiated into three parts: ▪ Proximal Convoluted tubule(PCT): It is the part nearer to the Bowman’s capsule. It lies in the renal cortex. ▪ Loop of Henle: It is the middle U shaped part of the tubule. It has an ascending limb and descending limb. It is found in the medulla region of the kidney. ▪ Distal Convoluted tubule(DCT): It is highly coiled found in the cortex of the kidney and opens into the collecting duct. Collecting duct: The open ends of many nephrons join into a wider tube called collecting tubule/collecting duct. This duct extends from cortex to medulla. The collecting duct receives the contents of many nephrons and pours the urine into the renal pelvis. Working of Nephron: Main function of nephron is to form urine. There are three main processes involved in the urine formation: Steps in urine formation: The kidney performs three functions as steps involved in urine formation - ultra-filtration, selective re-absorption and tubular secretion. 1. Glomerular ultrafiltration/Ultra-filtration occurs in the glomerulus where blood is filtered in the nephron. Minerals, waste and water are filtered, but red blood cells, proteins and large molecules are retained in our blood. When blood enters through the afferent arteriole which has larger diameter than the efferent arteriole (through which it leaves the Bowman’s capsule), it creates a pressure in the glomerulus. Under the influence of this hydrostatic pressure, all the liquid part of the blood along with some substances that are small enough to pass through the capillary walls are filtered out. This fluid in the Bowman’s capsule is called as glomerular filtrate(GF). Glomerular filtrate (GF) consists of water, urea, inorganic salts, amino acids, glucose and other plasma solutes. Blood coming out of the efferent arteriole has only blood cells, large protein and fat molecules. Page 5 of 9 Copyright © Global Indian International School  2. Selective tubular reabsorption involves reabsorption of some useful substances in the initial filtrate, such as glucose, amino acids, salts, and a major amount of water. These substances are reabsorbed from the renal tubule at various levels (PCT, Loop of Henle and DCT) into the blood capillaries surrounding the tubules (vasa recta). Urine is allowed to flow along the tube. 3. Tubular secretion: This occurs mainly in the DCT (distal convoluted tubule) and the CT (collecting duct) of the nephron. It is an active, vital process performed by the cells of the cuboidal epithelium lining the tubules which excrete additional wastes from the blood stream into the filtrate by active transport. In this process substances like potassium, hydrogen, creatinine and certain drugs like penicillin etc. are directly excreted by the tubular cells from the blood. The fluid which now flows through the last parts of the tubule is urine which consist of 95% water and 5% wastes such as ions of sodium, potassium and calcium, and nitrogenous wastes such as creatinine, urea and ammonia. Path of urine formation Renal Artery → Kidney → Afferent Arteriole → Glomerulus → Bowman’s Capsule ⎯⎯⎯⎯⎯→ (Ultrafiltration) → Proximal Convoluted Tubule (PCT) (Reabsorption) → Henle’s Loop (Reabsorption) → Distal Convoluted Tubule (DCT) (Reabsorption & Secretion) → Collecting Duct → Ureter ⎯⎯⎯→ Stores Urine in Urinary Bladder ⎯⎯⎯→ expels through Urethra (urethral peristalsis) Micturition The urinary bladder is stretched and gets filled with urine formed in the nephrons. The receptors present on the walls of the urinary bladder send signals to the Central Nervous System, thereby the bladder contracts and urethral sphincter muscles relax to release urine. This is known as micturition. Composition of Urine: Urine is a transparent, pale-yellow fluid which is, acidic in nature. Normal human urine consists of about 95% water and 5% of solid wastes. Besides the normal constituents, certain hormones and medicines like the antibiotic and excess water-soluble vitamins are passed out with urine. Organic compounds like Urea, Creatinine, Uric acid, Ammonia Inorganic Compounds like NaCl, KI Page 6 of 9 Copyright © Global Indian International School  Normally a man excretes 1000 - 1700 ml of urine daily, depending upon the water intake, diet, climate, mental state and physiological condition. Tea, coffee, alcohol and other beverages increases the formation of urine and are called diuretics. Osmoregulation and its importance: The process by which osmotic concentration (amount of water, minerals and salt) of the blood inside the body of a living being is maintained, is known as osmoregulation.  The kidneys together with the hypothalamus and the pituitary gland are responsible for the osmoregulation of blood in the body of human beings.  It is important for the survival of all living organisms as it helps to maintain the right concentration of solutes in their body fluids, which is necessary for normal cell function.  If there is more water, then the water moves into the cells by endosmosis causing them to swell and even burst.  If there is less water, then the water will move out of the cells causing them to shrink. Therefore, in both the cases, the cellular metabolism will be disrupted. When the body contains large amount of water, the tubules of nephrons in the kidney reabsorb very less water from the filtered urine. As a result, very dilute urine is produced and passed out.  But when the body contains less water, the tubules of nephrons in the kidney reabsorb more water from the filtered urine. As a result, concentrated urine is produced and passed out. Thus the kidneys not only help in filtration of nitrogenous wastes like urea but also help in osmoregulation. Antidiuretic hormone (ADH) – ADH is a hormone produce by the pituitary gland that regulates the amount of water reabsorbed by the kidney. When the body needs to conserve water, ADH is released, which increases the permeability of the DCT and CT, allowing more water to be reabsorbed back into the blood stream. If the secretion of ADH is reduced the urine production increases (less water is reabsorbed hence more urine). Nephron Vs Alveoli Alveoli and Nephrons are designed for the removal of wastes from the blood. Both have capillaries for filtration of the blood and removal of wastes. Alveoli in the lungs are basically balloon shaped structures to increase the surface area for gas exchange. They have an extensive network of blood capillaries to allow removal of CO2 from the blood and uptake fresh oxygen from the air. Nephrons are the working units of kidneys. They have a Bowman’s capsule, which again has an extensive capillary network and blood supply for removal of nitrogenous wastes i.e., Urea along with filtered water, salts, glucose etc. The important materials are reabsorbed before the urine is released from the nephron. Page 7 of 9 Copyright © Global Indian International School In the alveolar capillaries the blood flows at a lower pressure as compared to the capillaries present in the nephrons. The high blood pressure in the capillaries of nephrons helps in proper removal of water and dissolved wastes from the blood plasma. ARTIFICIAL KIDNEY: Hemodialysis simply dialysis is a process of purifying the blood of a person whose kidneys are not working normally. Blood drained from a convenient artery is pumped into a dialysing unit after adding an anticoagulant like heparin. The unit contains a coiled cellophane tube surrounded by a fluid (dialysing fluid) having the same composition as that of plasma except for the nitrogenous wastes. The porous cellophane membrane of the tube allows the passage of molecules based on a concentration gradient. As nitrogenous wastes are absent in the dialysing fluid, these substances freely move out, thereby clearing the blood. The cleared blood is pumped back to the body through a vein after adding anti heparin to it. In case of permanent damage to the kidneys, dialysis has to be performed for about twelve hours, twice a week. Patients with chronic kidney failure have been recorded to survive for more than 12 years on dialysis. Nowadays, diseased kidney may be replaced with healthy one by kidney transplantation. To lead a normal life, one healthy kidney is more than enough. Therefore, a healthy person can donate his kidney to patient who's both the kidneys are damaged. Page 8 of 9 Copyright © Global Indian International School Excretion in plants is by following methods a. Oxygen produced as a waste during photosynthesis, diffuses out of the leaf stomata. b. During the day carbon dioxide produced in respiration is used up in photosynthesis. c. Water in excess is removed by transpiration through the leaves. d. Some waste products are stored as resins and gums in old xylem. e. Latex (white fluid) is stored in stems and leaves of some plants. f. Elephant Yam tubers contain calcium oxalate crystals (Raphides). g. Many waste products are stored in vacuoles. h. Some waste products may get stored in the leaves which fall off. i. Plants excrete some waste materials into the soil around them. Page 9 of 9 Copyright © Global Indian International School