The correct option is (c) 2 and 3 only.
Explanation
The human excretory system functions to maintain homeostasis by filtering metabolic wastes from the blood. The functional units of the kidneys, called nephrons, perform this task through three main processes: glomerular filtration, tubular reabsorption, and tubular secretion.
Statement-wise Analysis
- Statement 1 is Incorrect. During the formation of urine, blood is filtered in the kidneys. However, useful substances such as glucose, amino acids, salts, and a major amount of water are not permanently excreted. They undergo selective reabsorption in the tubular part of the nephron and are returned to the blood capillaries.
- Statement 2 is Correct. The primary purpose of the excretory system is to remove nitrogenous metabolic wastes like urea and uric acid. These wastes are dissolved in water within the kidneys to form urine, which is then stored in the urinary bladder and expelled through the urethra.
- Statement 3 is Correct. Kidney failure (renal failure) results in the inability of the kidneys to filter blood effectively. This leads to the accumulation of toxic waste products, such as urea, in the blood. This condition is known as uremia and often requires hemodialysis to artificially remove wastes.
Key Takeaway
The kidneys act as a filtration system that removes dissolved metabolic wastes as urine while conserving essential nutrients and water through selective reabsorption.