Free Homeostasis MCQs with Answers

• A. the total of all chemical reactions in the body
• B. the removal of metabolic waste from the body
• C. the maintenance of a constant internal environment despite changes outside the body
• D. the growth of an organism to a fixed adult size

Explanation: Homeostasis keeps temperature, water potential, blood glucose and pH within narrow limits, because enzymes work properly only over a small…

• A. nephron
• B. neuron
• C. alveolus
• D. ureter

Explanation: Each kidney contains about a million nephrons, and every one carries out filtration, reabsorption and secretion on its own, so the organ's…

• A. active transport using ATP from the capsule cells
• B. the high hydrostatic pressure caused by the efferent arteriole being narrower than the afferent
• C. osmosis from the tubule into the capillary
• D. the beating of cilia in the capsule

Explanation: Blood enters the glomerulus through a wide afferent arteriole and leaves through a narrower efferent one, so pressure builds up and forces…

• A. Glucose
• B. Urea
• C. Sodium ions
• D. Plasma proteins

Explanation: The basement membrane acts as the real molecular sieve and holds back anything much larger than about 68,000 relative molecular mass, so…

• A. proximal convoluted tubule
• B. collecting duct
• C. loop of Henle
• D. Bowman's capsule

Explanation: The proximal tubule cells carry microvilli and many mitochondria because glucose and amino acids are recovered here by active transport…

• A. a larger Bowman's capsule
• B. more glomeruli per kidney
• C. a much longer loop of Henle, which builds a steeper salt gradient in the medulla
• D. no collecting ducts

Explanation: The loop works as a countercurrent multiplier, making the medulla progressively saltier towards the tip, and the collecting duct passing…

• A. increasing the rate of glomerular filtration
• B. making the walls of the distal tubule and collecting duct more permeable to water
• C. actively pumping water out of the tubule
• D. reducing the reabsorption of sodium ions

Explanation: ADH from the posterior pituitary inserts water channels into the tubule walls, so more water is reabsorbed by osmosis into the salty…

• A. diabetes mellitus
• B. kidney stones
• C. a urinary tract infection
• D. diabetes insipidus

Explanation: Diabetes insipidus results from a lack of ADH or a failure of the tubule to respond to it, so water cannot be reabsorbed and the patient…

• A. sodium ions
• B. glucose
• C. urea
• D. plasma proteins

Explanation: Aldosterone stimulates the distal tubule and collecting duct to pump sodium back into the blood in exchange for potassium, and since water…

• A. ammonia
• B. urea
• C. uric acid
• D. creatine

Explanation: Surplus amino acids are deaminated in the liver and the toxic ammonia produced is converted at once into far less toxic urea by the…

• A. uric acid is more toxic and so must be removed faster
• B. they have no liver in which to make urea
• C. uric acid is almost insoluble and can be excreted as a paste, saving water
• D. uric acid contains no nitrogen

Explanation: Being nearly insoluble, uric acid can be voided as a semi solid with very little water, which suits animals that must conserve water and…

• A. the dialysis fluid contains enzymes that destroy urea
• B. the blood is heated so that urea evaporates
• C. urea is actively pumped across the membrane
• D. the dialysis fluid contains no urea, so urea diffuses out across a partially permeable membrane

Explanation: Dialysis fluid is made with the same concentrations of glucose and mineral ions as normal blood plasma but with no urea at all, so only…

• A. the blood glucose level exceeds the capacity of the tubule carriers to reabsorb it
• B. glucose is too large to be reabsorbed
• C. the glomerulus stops filtering glucose
• D. insulin is secreted into the filtrate

Explanation: Reabsorption of glucose depends on a fixed number of carrier proteins in the proximal tubule, and once the blood concentration passes the…

• A. medulla oblongata
• B. hypothalamus
• C. cerebellum
• D. skin itself

Explanation: The hypothalamus contains receptors that monitor the temperature of the blood flowing through it and also receives information from…

• A. constrict, so less blood reaches the surface
• B. are unaffected, since only sweating matters
• C. dilate, so more blood flows near the surface and more heat is lost
• D. carry blood away from the skin into deeper shunt vessels

Explanation: Vasodilation of the arterioles lets more warm blood flow through the surface capillaries, so heat is lost by radiation and conduction and…

• A. sweat is colder than the body
• B. sweat carries away dissolved urea
• C. the sweat glands use up energy in secreting it
• D. evaporation of the water in sweat takes latent heat from the skin

Explanation: Changing liquid water into vapour requires a large amount of latent heat, and that heat is drawn from the skin surface, so the body cools…

• A. rapid involuntary muscle contractions release heat from respiration
• B. it increases the blood flow to the skin
• C. it reduces the surface area of the body
• D. it stops sweat being produced

Explanation: The muscles contract and relax rapidly without doing any useful external work, so almost all the energy released by increased respiration…

• A. dilation of the surface capillaries
• B. contraction of the erector pili muscles, which pull the hairs upright
• C. the emptying of the sweat glands
• D. the thickening of the subcutaneous fat layer

Explanation: Each hair has a small erector muscle that pulls it erect, and in a furry mammal this traps a thicker layer of still air as insulation.

• A. always live in warm climates
• B. have a body temperature that follows the temperature of the surroundings
• C. generate most of their body heat from their own metabolism and hold it nearly constant
• D. are unable to lose heat through the skin

Explanation: An endotherm keeps its core temperature steady using heat from respiration, which lets enzymes work at their optimum whatever the weather…

• A. The passing of undigested cellulose in faeces
• B. The loss of dead cells from the surface of the skin
• C. The removal of hair when it is cut
• D. The removal of carbon dioxide by the lungs

Explanation: Excretion is the removal of the waste products of the body's own metabolism, and carbon dioxide is made by respiration inside every cell…