Free Kidney and Urinary System MCQs with Answers

• A. 25 degrees Celsius
• B. 30 degrees Celsius
• C. 37 degrees Celsius
• D. 42 degrees Celsius

Explanation: Enzymes of the body work best near 37 degrees, and the hypothalamus holds temperature within a degree of this set point.

• A. endotherms
• B. homeotherms
• C. warm blooded animals
• D. ectotherms

Explanation: Ectotherms gain heat from outside sources and so track ambient temperature, whereas endotherms generate their own heat metabolically.

• A. constrict, reducing heat loss from the surface
• B. dilate widely to warm the skin
• C. burst under pressure
• D. stop carrying blood altogether

Explanation: Vasoconstriction keeps warm blood in the core, which is why skin looks pale in the cold.

• A. shivering thermogenesis
• B. behavioural thermoregulation
• C. chemical heat production
• D. evaporative cooling

Explanation: Since reptiles cannot raise temperature metabolically, they move between sun and shade to manage it.

• A. producing heat through metabolism
• B. increasing blood flow to the surface
• C. insulating the body against heat loss
• D. absorbing sunlight

Explanation: Subcutaneous fat conducts heat poorly, so it keeps core warmth in, which is why marine mammals carry thick blubber.

• A. panting draws cold air into the lungs
• B. dogs sweat heavily from the skin
• C. panting raises the metabolic rate
• D. evaporation from the tongue and airways removes heat

Explanation: With few sweat glands, dogs rely on evaporating water from the moist surfaces of the mouth and lungs.

• A. negative feedback
• B. positive feedback
• C. hormonal rhythm
• D. conditioned reflex

Explanation: Any deviation from the set point triggers responses that reverse it, the defining feature of negative feedback.

• A. brain
• B. liver and other metabolically active organs
• C. skin
• D. bones

Explanation: The liver's constant metabolism releases enough heat at rest to dominate body warmth, while during hard exercise skeletal muscle takes…

• A. hyperthermia
• B. fever
• C. hypothermia
• D. heat stroke

Explanation: Hypothermia slows enzymes and eventually the heart, and it is treated by gradual rewarming.

• A. undigested food from the intestine
• B. excess water only
• C. dead cells from the skin surface
• D. metabolic waste products formed in the cells

Explanation: True excretion eliminates substances made by metabolism, such as urea and CO2.

• A. lungs
• B. kidneys
• C. liver
• D. skin

Explanation: CO2 diffuses into the alveoli and is breathed out, so the lungs are the principal organ of its removal.

• A. kidney
• B. liver
• C. lungs
• D. intestine

Explanation: The liver runs the ornithine cycle, turning toxic ammonia from amino acid breakdown into urea, which the kidneys then filter out.

• A. too large a molecule to transport
• B. highly toxic even in low concentrations
• C. needed for protein synthesis
• D. insoluble in water

Explanation: Ammonia raises pH and poisons cells, particularly neurons, so it must be detoxified at once.

• A. glucose and protein
• B. urea and hormones
• C. amino acids and fats
• D. mineral salts and a little urea

Explanation: Sweat is mostly water with dissolved salts and traces of urea, so sweating causes both water and salt loss that must be replaced.

• A. excreting urea through the stomata
• B. sweating from the leaves
• C. releasing ammonia through the roots
• D. storing wastes in leaves that later fall

Explanation: Plants lack excretory organs, so they deposit wastes as resins, crystals or in old leaves that are then shed.

• A. is almost insoluble in water, so very little water is lost
• B. is highly soluble in water
• C. is converted to urea in the cloaca
• D. is released as a gas

Explanation: Precipitating uric acid saves water and keeps the egg clean, since an embryo sealed in a shell cannot dilute soluble wastes.

• A. uricotelic
• B. ammonotelic
• C. ureotelic
• D. phototelic

Explanation: Mammals and adult amphibians are ureotelic, balancing toxicity against water cost.

• A. regular blood transfusions only
• B. a heart lung machine
• C. dialysis or a kidney transplant
• D. a high protein diet

Explanation: Dialysis artificially filters wastes from the blood while a transplant can restore real function.

• A. Nephron
• B. Neuron
• C. Glomerulus
• D. Collecting duct

Explanation: The nephron is the functional unit of the kidney, consisting of glomerulus, tubules, and associated structures.

• A. Proximal convoluted tubule
• B. Bowman's capsule
• C. Loop of Henle
• D. Collecting duct

Explanation: Ultrafiltration occurs in the glomerulus/Bowman's capsule, where blood is filtered under pressure.