Chapter 16 of Class 11 Biology is Excretory Products and their Elimination. It covers modes of nitrogenous waste excretion, the human excretory system, urine formation, and osmoregulation. These Class 11 Biology Chapter 16 solutions are also useful as quick revision notes before exams.
Modes of Excretion
Ammonotelism: excretion of ammonia (aquatic animals, highly toxic but very soluble, needs lots of water). Ureotelism: excretion of urea (mammals, less toxic, converted from ammonia in the liver). Uricotelism: excretion of uric acid (birds, reptiles, insects, least toxic, semi-solid, conserves water — adaptation for terrestrial/limited-water environments).
Human Excretory System
Consists of a pair of kidneys, ureters (carry urine to bladder), urinary bladder (stores urine), and urethra (expels urine). Functional unit of the kidney: nephron (Malpighian corpuscle + renal tubule).
Urine Formation: Three Steps
Glomerular filtration: blood pressure forces fluid from glomerular capillaries into Bowman’s capsule, forming filtrate. Reabsorption: useful substances (glucose, amino acids, most water, ions) are reabsorbed back into blood, mainly in the proximal convoluted tubule (PCT). Secretion: additional waste substances (H⁺, K⁺, some drugs) are actively secreted into the tubule from blood, mainly in the distal convoluted tubule (DCT).
Counter-Current Mechanism
The loop of Henle and vasa recta work together via a counter-current mechanism to maintain a gradient of increasing osmolarity in the medulla, enabling the kidney to produce concentrated urine and conserve water.
Regulation of Kidney Function
ADH (antidiuretic hormone/vasopressin): increases water reabsorption (in response to low blood volume/high osmolarity), reducing urine volume. Renin-angiotensin-aldosterone system (RAAS): regulates blood pressure and sodium reabsorption in response to low blood pressure/volume.
Class 11 Biology Chapter 16 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 11 Biology Chapter 16 Extra Questions and Class 11 Biology Chapter 16 Revision Notes for quick revision and extra practice.
