All Free Biology MCQs with Answers

2061. Length of membranous urethra is about ___________ ?

• A. 1 cm
• B. 2 cm
• C. 5 cm
• D. 9 cm

Explanation: The membranous urethra is the shortest part of the male urethra and is about 1 cm long. Students may choose 2 cm because some references give an approximate value near 1.25 cm, but 1 cm is the closest option.

2062. Which of the following organ is responsible for blood filtration:

• A. Liver
• B. Kidney
• C. Lungs
• D. Heart

Explanation: The kidneys filter blood through millions of nephrons, removing nitrogenous wastes and excess water to form urine while retaining useful substances. Students may choose the liver because it detoxifies blood, but it does not perform the main filtration process that produces urine.

2063. Mammalian kidney, under restricted water supply can conserve water by over ________ % reabsorption of glomerular filtrate

• A. 80.50%
• B. 90.50%
• C. 95.50%
• D. 99.50%

Explanation: The kidneys normally reabsorb about 99% of glomerular filtrate, and under restricted water supply reabsorption can exceed 99.5%, leaving only a small volume as urine. The lower values describe ordinary or incomplete reabsorption and do not represent maximum water conservation; 99.5% is the intended textbook value.

2064. Which of the following filtrate contains excessive amount of amino acids, glucose, and salts?

• A. Glomerular filtrate
• B. Filtrate passing through ascending limb
• C. Filtrate passing through distal conveluted tubule
• D. Filtrate passing through collecting tubules

Explanation: Glomerular filtrate contains water, salts, glucose and amino acids because these small molecules pass through the filtration barrier from blood. Most glucose and amino acids are later reabsorbed, so filtrate in the tubules contains much less of them; students may choose distal tubular filtrate by overlooking this reabsorption.

2065. A stone measuring 0.4 cm, blocking the outlet of renal pelvis resulting in mild to moderate tract obstruction. Which of the following technique will be opted to remove this stone?

• A. Kidney surgery
• B. Burring a hole and removing the stone manually (nephrolithotomy)
• C. Extracorporeal Shock wave lithotripsy
• D. None of these

Explanation: A 0.4 cm stone equals 4 mm, and a stone of this size causing mild to moderate obstruction is commonly treated by extracorporeal shock-wave lithotripsy, which fragments it without an incision. Nephrolithotomy is a more invasive procedure and may be selected for larger or otherwise difficult stones, so choosing it over lithotripsy ignores the small stone size.

2066. Which of the vascular channels are related to Juxtramedullary nephrous only?

• A. Afferent and efferent arterioles
• B. Peritubualr capillaries
• C. Vasa nervosa
• D. Vasa recta

Explanation: Vasa recta are straight capillaries that run alongside the loops of Henle in juxtamedullary nephrons and help maintain the medullary concentration gradient. Peritubular capillaries occur around the tubules of both cortical and juxtamedullary nephrons, so choosing them is too general.

2067. Which of the following fish drink large amount of sea water and excrete concentrated urine resulting in maximum salt excretion and minimal water loss?

• A. Hagfish
• B. Fresh water fishes
• C. Bony fishes
• D. None of these

Explanation: Marine bony fishes drink seawater because they lose water by osmosis, and their kidneys produce concentrated urine to remove excess salts while conserving water. Students may choose hagfish because it is a marine fish, but hagfish have body fluids closer to seawater and do not show the typical seawater-drinking pattern of marine bony fishes.

2068. Which of the following mechanism explains development of anemia in Renal failure?

• A. Failure of bone marrow is accompanied with renal failure.
• B. Destruction of RBC results from accumulated urea in the blood.
• C. Chronicity of the disease is respobsible for anemia
• D. Failure of proper RBC synthesis, due to lack of chemical stimulation.

Explanation: Damaged kidneys produce less erythropoietin, the hormone that stimulates bone marrow to form red blood cells, so renal failure can cause anaemia. Students may choose b because urea accumulates in renal failure, but reduced erythropoietin stimulation is the main mechanism described here.

2069. Which of the following constituent is/are maximum in the filtrate that leaves proximal convoluted tubules?

• A. Glucose
• B. Amino acids
• C. Nitrogenous waste
• D. All of these

Explanation: Glucose and amino acids are normally reabsorbed almost completely from the filtrate in the proximal convoluted tubule, whereas nitrogenous wastes such as urea largely remain in the tubular fluid. Students may choose d because all three substances enter the initial filtrate, but glucose and amino acids do not remain in maximum amounts after PCT reabsorption.

2070. On which of the following site the posterior pituitary hormone acts predominantly?

• A. Proximal convoluted tubule
• B. Descending limb of loop of Henle
• C. Ascending limb of loop of Henle
• D. Collecting tubules

Explanation: Antidiuretic hormone from the posterior pituitary acts mainly on collecting tubules, increasing their permeability to water and allowing concentrated urine to form. Students may choose the proximal convoluted tubule because extensive reabsorption occurs there, but ADH specifically regulates water permeability in the collecting tubules.