Answer: Option B. -> Urinary bladder
:
B
The elastic and flexible organ in the human excretory system is urinary bladder. Itstores urine temporarily before it is expelled out through the process of urination. The urinary bladder is a pear-shaped muscular sac which iscapable of expanding as urine gets collected in it.

Answer: Option A. -> Spinach and beet root have more calcium oxalate.
:
A
Calcium oxalate is an excretory product of plants stored in vacuoles of plant cells and they are the main components of kidney stones. This compound is abundant in spinach and beet roots. So they are notincluded in diet to avoid further complications in a person suffering fromkidney stones.

Answer: Option B. -> i) ⇒ d, ii) ⇒ c, iii) ⇒ b, iv) ⇒ 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 B. -> I and IV
:
B
Urea, uric acid and ammonia are all nitrogenous wastes and excretory products. Ammonia is highly toxic and highly soluble in water, therefore, requires a large amount of water for excretion. Urea is less toxic and less soluble in water than ammonia. Uric acid crystals are non-toxic and almost insoluble in water. So their level of toxicity and the amount of water needed for their elimination differs for each of them.

Answer: Option B. -> Constant composition of the blood.
:
B
Kidneys ensure that the pH balance, osmolarity and general composition of our blood is maintained in a stable range, irrespective of how much waste is produced by filtering the blood, excreting certain substances and reabsorbing certain others. It helps in maintaining a balance in blood composition. ADH (Antidiuretic hormone) acts on the kidneys to reabsorb water and is secreted and controlled by the pituitary gland.

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 A. -> 125 mL
:
A
The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. On an average,
1100-1200 ml of blood is filtered by the kidneys per minute. The amount of the filtrate formed by the kidneys per minute is called glomerular filtration rate (GFR). GFR in a healthy individual is approximately 125 ml/minute, i.e., 180 litres per day.

Answer: Option D. -> Homogentisic acid
:
D
Alkaptonuria (black urinedisease,blackbone disease, or alkaptonuria) is a rare inherited genetic disorder in which the body cannot process the amino acids phenylalanine and tyrosine, which occur in protein.Homogentisic acidand its oxidised form alkapton are excreted in theurine, giving it an unusually dark colour.

Answer: Option D. -> Transitional epithelium 
:
D
Transitional epitheliumis a layer of cells that forms the mucosal lining of your ureters, a portion of your urethra, and your urinarybladder. The function oftransitional epitheliumcells is to protect theurinarysystem against the toxic effects ofurine. Additionally,transitional epitheliumcells stretch to accommodate the volume of thebladderand other organs when they fill with liquid.

Answer: Option B. -> The excretory volume of urine increases
:
B
Diuresis is when the body has too much of certain substances in the fluid that the kidneys filter. Eventually this fluid becomes urine and increases the amount of water expelled by the body, leading to an increased or excessive urination.