Homeostasis: Practice Questions

• a.A state where the external environment is modified to match the internal body temperature.
• b.A process where positive feedback loops are used to prevent any change in the internal environment.
• c.A state where internal conditions fluctuate within narrow limits around a set point.
• d.A state where internal conditions are kept at an absolutely constant value at all times.

• a.

  Fluctuations in pH cause the blood plasma to become hypertonic, resulting in the lysis of red blood cells due to excessive water uptake via osmosis.

• b.

  A change in pH alters the hydrogen bonding and ionic interactions within the tertiary structure of enzymes, leading to denaturation and a loss of metabolic function.

• c.

  A high blood pH levels stimulate a positive feedback loop within the bicarbonate buffer system, leading to an uncontrolled increase in carbon dioxide concentration.

• d.

  A significant decrease in pH increases the affinity of haemoglobin for oxygen, which prevents the effective release of oxygen to the respiring tissues.

• a.

  The hypothalamus stimulates the release of adrenaline from the adrenal glands to increase the basal metabolic rate.

• b.

  The parasympathetic nervous system stimulates the contraction of erector pili muscles to trap a layer of air.

• c.

  The hypothalamus sends sympathetic nerve impulses to cause vasodilation of peripheral arterioles.

• d.

  Thermoreceptors in the skin send impulses to the cerebrum to initiate voluntary shivering in skeletal muscles.

• a.

  Urea is actively transported out of the limb to increase the water potential of the medulla.

• b.

  Sodium and chloride ions are actively transported out into the interstitial fluid while the limb remains impermeable to water.

• c.

  Sodium and chloride ions diffuse into the tubule from the vasa recta to maintain the osmotic gradient.

• d.

  Water is reabsorbed into the interstitial fluid by osmosis while the limb is impermeable to sodium ions.

• a.

  ADH binds directly to the luminal membrane and acts as a channel protein, allowing water to flow from the filtrate into the cell by active transport.

• b.

  ADH binds to receptors on the basal membrane, triggering a second messenger system that causes vesicles containing aquaporins to fuse with the luminal membrane.

• c.

  ADH enters the cell nucleus and binds to transcription factors to increase the expression of genes that code for sodium-glucose co-transporter proteins.

• d.

  ADH activates sodium-potassium pumps on the luminal membrane, creating a steep electrochemical gradient that pulls water into the blood through simple diffusion.

Write your answer out first, then check it against the worked solution.

Write your answer out first, then check it against the worked solution.

Write your answer out first, then check it against the worked solution.