31 Years NEET Previous Year Questions: Excretory Products & Their Elimination

From Bowman's capsule, glomer ular filtrate enters the proximal convolute tubule. Most of the useful substances like Glucose (all), Amino Acids (all), most of the inorganic ions (Na⁺, K⁺, Cl^– etc), most of the important buffer bicarbonates are reabsorbed in Proximal Convoluted Tubule. Cells are specially adaptive for absorption having numerous microvilli & mitochondria (to provide energy for active absorption).

Proximal convoluted tubule (PCT) is lined by simple cuboidal brush border epithelium. The brush border epithelium increases the surface area for reabsorption. Nearly all of the essential nutrients, and 70-80 percent of electrolytes. Hence brush border is characteristic of the proximal convoluted tubule.
So, the correct answer is 'Proximal convoluted tubule'.

Nephron is the excretory unit of human excretory system. Each nephron has a Bowman’s Capsule, a Proximal Convoluted Tubule (PCT), Loop of Henle (Descending & Ascending limbs) and Distal Convoluted Tubule (DCT) which then enter into collecting duct.

The cells of Proximal Convoluted Tubule (PCT) reabsorb entire glucose, amino acids, most of the inorganic ions (Na⁺, K⁺, Cl^–)  much of the water as well as some urea. Glucose is reabsorbed actively and most effectively.

Ammonia molecules are small and very soluble in water. In ammonotelic animals large amount of H₂O is required to eliminate ammonia from the body, so it is found in aquatic animals like tadpole of frog. When tadpole becomes a mature frog it acquires mainly ureotelism.

Active transport.

Correct option: A.

Hairs are epidermal derivatives; the visible hair shaft is formed of dead, keratinised cells.

The cells that actively produce hair are present in the hair matrix at the base of the follicle and are associated with the hair papilla, which contains living connective tissue and blood vessels that nourish the matrix cells.

After keratinisation, the cells form the hair shaft and lose viability; the shaft is organised into three layers: cuticle, cortex and medulla.

Hence, hairs are epidermal in origin and (as usually observed in the shaft) are made of dead cells, so option A is correct.

The uriniferous tubule or the kidney tubule is a fine, long, convoluted tubule that is involved in excretory functions. This tubule basically conveys urine from the glomerulus to the renal pelvis. A large amount of water and salts are reabsorbed during the passage of urine through it.

The nephrons along with collecting ducts are called as uriniferous tubule.The body of the nephron is divided into  Bowman's capsule, PCT, Henle's loop and DCT.

So, the correct answer is 'Glomerulus'.

If kidneys fail to reabsorb water the urine will be diluted causing polyuria (frequent urination). Then the body tissues get dehydrated & the cell will loose water content & shrink.

The excretion of uric acidis called uricotelism. The excretion of uric acid is advantageous for those animals which have to conserve water for their survival like birds and lizards.

In patients affected with cholera, a cholera enterotoxin is produced which results in increased synthesis of intracellular cyclic AMP, which in turn increases the  permeability of intestinal mucosa, leading to secretion of fluid throughout the small intestine. Hence the patient is given saline drip whereby Na⁺ ions restore the osmotic balance by retaining water in the body.

In  ureotelic animals urea is formed from ammonia  by Ornithine cycle. 

In ureotelic animals urea is formed by Ornithine cycle. Urea is formed in the liver where two molecules of ammonia combine with one molecule of CO₂ in presence of Ornithine, citrulline, arginine and enzyme arginase. This is called Ornithine cycle.

Nephridia are the excretor y str uctures of annelids. Henle's loop is a part of the nephron or uriniferous tubule of the vertebrate kidney.

Correct answer: A - Platyhelminthes.

Solenocytes are specialised excretory cells associated with protonephridia; each solenocyte has a single long flagellum that helps draw waste-containing fluid into the tubule for removal.

In Platyhelminthes, the excretory system is mainly protonephridial, composed of flame cells and solenocytes, which help in osmoregulation and removal of nitrogenous wastes (primarily ammonia).

By contrast, Annelids possess nephridia (metanephridia) as their excretory organs. Molluscs typically have paired nephridia or a kidney-like organ. Echinodermata eliminate nitrogenous wastes mainly by diffusion across the body surface and through dermal structures such as papulae and tube feet.

Growth hormone, released by the anterior lobe of pituitary brings about body growth by synthesis and deposition of proteins in tissues. Renin secreted by special cells in kidneys regulates blood pressure. Aldosterone reduces Na⁺ elimination by helping active reabsorption from the nephric filtrate.

Henle’s loop is involved in osmoregulation and concentrating  urine. Thus producing a hypertonic urine.

The nephridia are the excretory organs. The nephridia in earthworm are  – Septal nephridia, Pharyngeal nephridia and Integumentary nephridia. The septal nephridia do not discharge excretory fluid to the exterior rather it pour them into the intestine. Hence these are also called Enteronephric nephridia.

Sweat  regulates body temperature. Sweating also called perspiration or sometimes transpiration is the production and evaporation of a fluid, consisting primarily of water as well as a smaller amount of sodium chloride the main constituent of “table salt”, that is excreted by the sweat glands in the skin of mammals.

Hydra being a coelenterate, has blind sac body plan. It has only one mouth which serves as the opening for ingestion and waste elimination besides diffusion across body wall. 

Henle’s loop is associated with  the concentration of urine and production of hypertonic urine.

Fresh water protozoans live in hypotonic solution so, for regulation of excess of water which comes in the protoplasm through the process of endosmosis, contractile vacuoles have developed, When these protozoans are placed in marine water i.e., hypertonic water, the contractile vacuoles become disappear because the process of endosmosis does not happen and thus, water does not come in the protoplasm.

In uricotelic animals nitrogenous waste is eliminated in the form of uric acid. Ammonotelism is seen in aquatic animals wherein nitrogenous wastes is eliminated in the form of ammonia eg. Fishes, tadpole. Ureotelism is observed in human beings in which nitogenous waste is eliminated as urea.

Terrestial animals have limited access to water. Hence they have to secrete hypertonic urine and conserve water. Choices (c) and (d) are characteristics of marine animals who need to overcome the problem of preventing entry of salts and loss of water. Choice (a) is characteristic of fresh water animals.

If a person is undergoing prolonged fasting, his urine will be found to contain abnormal quantities of ketones. During fasting energy is obtained by the oxidation of reserved fats. As a result of fatty acid oxidation large amount of ketone bodies are produced such as acetoacetate, (3-hydroxybutyrate and acetone.