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Excretory Products and their Elimination NCERT Textbook With Solutions PDF Free Download
Chapter 19: Excretory Products and their Elimination
Animals accumulate ammonia, urea, uric acid, carbon dioxide, water, and ions like Na +, K+ , Cl– , phosphate, sulfate, etc., either by metabolic activities or by other means like excess ingestion.
These substances have to be removed totally or partially. In this chapter, you will learn the mechanisms of elimination of these substances with special emphasis on common nitrogenous wastes.
Ammonia, urea, and uric acid are the major forms of nitrogenous wastes excreted by animals.
Ammonia is the most toxic form and requires a 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 necessitated the production of lesser toxic nitrogenous wastes like urea
and uric acid for the conservation of water.
Mammals, many terrestrial amphibians, and marine fishes mainly excrete urea and 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 the desired osmolarity.
Reptiles, birds, land snails, and insects excrete nitrogenous wastes as uric acid in the form of a pellet or paste with a minimum loss of water and are called uricotelic animals.
A survey of the animal kingdoms presents a variety of excretory structures. In most invertebrates, these structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys.
Some of these structures are mentioned here. Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids, and the cephalochordate – Amphioxus.
Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation.
Nephridia are the tubular excretory structures of earthworms and other annelids.
Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance. Malpighian
tubules are the excretory structures of most insects including cockroaches.
Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation. Antennal glands or green glands perform the excretory function in crustaceans like prawns.
In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder, and a urethra (Figure 19.1).
Kidneys are reddish-brown, bean-shaped structures situated between the levels of the last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity.
Each kidney of an adult human measures 10-12 cm in length, 5-7 cm in width, and 2-3 cm in thickness with an average weight of 120- 170 g.
Towards the center of the inner concave surface of the kidney is a notch called the hilum through which the ureter, blood vessels, and nerves enter.
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NCERT Solutions Class 11 Biology Chapter 19 Excretory Products and their Elimination
1. Define Glomerular Filtration Rate (GFR)
Glomerular Filtration Rate (GFR) is the amount of filtrate formed by both the kidneys (nephrons) every minute. The GFR of a healthy person is approximately 125ml per minute. The GFR consists majorly of water and other constituents such as amino acids, glucose, potassium, sodium, urea, uric acid, and ketone bodies.
2. Explain the autoregulatory mechanism of GFR.
Kidneys regulate the glomerular filtration rate through the mechanism which is auto regulatory. It involves the action of the juxtaglomerular apparatus, which is a microscopic structure present between the returning distal convoluted tubule and vascular pole of the renal corpuscle of the same nephron.
It regulates the glomerular filtration rate and renal blood flow. When the glomerular filtration rate declines, the juxtaglomerular cells are activated for the release of renin. This triggers the glomerular blood flow causing the GFR to revert to normal. Renin causes GFR to revert to normalcy by activating the renin-angiotensin mechanism.
3. What is meant by the term osmoregulation?
Osmoregulation is the process of regulating the osmotic concentration in the cells of the body by checking the quantity of water and salts.
4. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?
Ammonia is an extremely toxic nitrogenous waste. In order to reduce the toxicity of ammonia in the body, a very large amount of water is necessary.
To dilute ammonia, the bodies of terrestrial animals do not possess an adequate quantity of water. If the body of terrestrial animals stores this excess ammonia, it may turn extremely poisonous for them.
Hence in such animals, ammonia is always converted to less toxic uric acid and urea. This is the reason why terrestrial animals are generally either uricotelic or ureotelic.
NCERT Class 11 Biology Textbook Chapter 19 Excretory Products and Their Elimination With Answer PDF Free Download