Answer: Option A. -> Impermeable to water and Sodium chloride (NaCl)
:
A
Countercurrent exchanger would not exist if there were not some mechanism to initially make the vasa recta more concentrated at the bottom of the loop. This is accomplished by the loop of Henle. The ascending limb of Henle and the early distal tubule are impermeable to water as indicated by their thick wall. These regions actively transport sodium chloride (NaCl) out of the filtrate and into the surroundings. The NaCl diffuses into the descending limb of the vasa recta. It will not diffuse into the ascending vasa recta because that fluid is already highly concentrated. This is the mechanism that 'multiplies' the concentration of NaCl in the descending vasa recta making the countercurrent exchanger possible

Answer: Option D. -> Hydrochloric acid
:
D

Mammals such as humans excrete urea and ammonia while birds, reptiles and some terrestrial invertebrates produce uric acid as waste. Uricotelic organisms tend to excrete uric acid waste in the form of a white paste or powder. Hydrochloric acid is not the waste product excreted by the animal. 

Answer: Option C. -> Afferent glomerular arteriole is wider than efferent glomerular arteriole
:
C

The diameter of the afferent (incoming) arteriole is greater than the diameter of the efferent arteriole (by which blood leaves the glomerulus). As a result, there is no drop in blood pressure that would usually occur when blood flows from the arterial end to the venous end in capillaries. The maintenance of high pressure drives glomerular filtration.

Answer: Option A. -> Henle's loop
:
A

In the kidney, the loop of Henle is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. The main function of loop of Henle is to create a concentration gradient in the medulla of the kidney

Answer: Option B. -> i) $\Rightarrow$ d, ii) $\Rightarrow$ c, iii) $\Rightarrow$ b, iv) $\Rightarrow$ a
:
B

Pressure filtration - Blood pressure forces molecules from the blood into the glomerular capsule. Examples of molecules - water, glucose, urea. Selective reabsorption - Diffusion and active transport, return molecules to blood at the proximal distal convoluted tubule. Example of molecules - water, glucose, amino acids. Tubular secretion - Active transport moves molecules from blood into the distal convoluted tubule. Example of molecules - penicillin.

 Excretion - Urine formation aids the body to get rid of metabolic waste. Example of molecules - Urea and uric acid.

Answer: Option A. -> Micturition will be uncontrolled.
:
A

Sensory stretch receptors are responsible for stretch reflex. If these are removed then there will be no more autonomic nervous control and urge to micturition will be uncontrolled. Micturition is the expulsion of urine from the urinary bladder.

Answer: Option A. -> 1 - Kidney, 2 - Ureter, 3 - Urinary bladder, 4 - Urethra
:
A

The urinary system in humans consists of one pair of kidneys (1) and the corresponding pair of ureters (2) that collect the urine formed and move it to a urinary bladder (3) that stores the urine until it can be excreted out through a tube called the urethra (4).

Answer: Option C. -> Ultrafiltration, tubular reabsorption and tubular secretion
:
C
Urine formation in humans takes place by three processes - ultrafiltration, tubular reabsorption and secretion. It takes place in the Malpighian corpuscle, Henle’s loop PCT and DCT. Blood is filtered so finely through the membranes of bowman's capsule, that almost all the constituents of the plasma except the proteins pass onto the lumen of the Bowman’s capsule. Therefore, it is considered as a process of ultra filtration. A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released (1.5 litres), suggest that nearly 99 per cent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption. The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms. During urine formation, the tubular cells secrete substances like $H^{+}$, $K^{+}$ and ammonia into the filtrate. Tubular secretion is also an important step in urine formation as it helps in the maintenance of ionic and acid-base balance of body fluids.

Answer: Option D. -> When someone drinks a lot of water, ADH release is suppressed
:
D

Antidiuretic hormone (ADH) or vasopressin increases the reabsorption of water in the distal convoluted tubule, collecting tubules and collecting ducts of the nephrons in the kidneys. As a result, the reabsorption of water from the glomerular filtrate is increased. When someone drinks a lot of water, requirement of absorption of water decreases, so ADH release is suppressed.

Answer: Option D. -> The urine will be more dilute
:
D
Henle's loop is associated with reabsorption of water and electrolytes making the urine more concentrated. Special arrangement of Henle’s loop and vasa recta is called the counter current mechanism. This mechanism helps to maintain a concentration gradient in the medullary interstitium. Presence of such interstitial gradient helps
in an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine). Human kidneys can produce urine nearly four times concentrated than the initial filtrate formed.