Free Homeostasis MCQs with Answers

• 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.

• A. Proximal tubule
• B. Descending limb
• C. Collecting duct
• D. Glomerulus

Explanation: ADH (vasopressin) increases water permeability of the collecting duct by inserting aquaporins.

• A. Blood pressure
• B. Concentration gradient in medulla
• C. Glomerular filtrate
• D. Urea

Explanation: The counter-current multiplier in the loop of Henle establishes a hypertonic gradient in the renal medulla.

• A. Water excretion
• B. Sodium reabsorption
• C. Potassium reabsorption
• D. Glucose excretion

Explanation: Aldosterone increases Na+ reabsorption and K+ secretion in the distal tubule and collecting duct.

• A. Kidneys
• B. Liver
• C. Muscles
• D. Brain

Explanation: Urea is formed in the liver from ammonia (toxic) via the ornithine/urea cycle.

• A. Adrenal cortex
• B. Juxtaglomerular cells
• C. Pituitary
• D. Hypothalamus

Explanation: Juxtaglomerular cells in the afferent arteriole secrete renin in response to low blood pressure.

• A. Blood glucose is normal
• B. Blood glucose exceeds renal threshold
• C. ADH is high
• D. Aldosterone is low

Explanation: Glycosuria (glucose in urine) occurs when blood glucose exceeds the renal threshold (~180 mg/dL), saturating reabsorption capacity.

• A. Blood pressure
• B. Urine output
• C. Sodium excretion
• D. Potassium reabsorption

Explanation: The renin-angiotensin-aldosterone system (RAAS) ultimately increases blood pressure through vasoconstriction and Na+/water retention.

• A. Insulin deficiency
• B. ADH deficiency
• C. Aldosterone excess
• D. Renin deficiency

Explanation: Diabetes insipidus results from ADH deficiency or resistance, causing inability to concentrate urine and excessive dilute urine.

• A. Hypotonic urine with decreased volume
• B. Hypotonic urine with increased volume
• C. Hypertonic urine with decreased volume
• D. Hypertonic urine with increased volume

Explanation: ADH makes the distal tubule and collecting duct permeable to water, so water is reabsorbed into the salty medulla and a small volume of…

• A. The filtration of blood to remove metabolic waste
• B. The regulation of solute and water movement between an organism and its environment
• C. The creation of an osmotic gradient in the kidney medulla
• D. The secretion of hormones that control blood plasma

Explanation: Osmoregulation is the control of water and solute balance so that the water potential of body fluids stays steady, whatever the organism…