Which of the following statements about the role of the kidneys or lungs in the maintenance of acid-base balance is FALSE?

Question 8: Which of the following molecules cannot pass through the plasma membrane?

The plasma membrane is selectively permeable. Small, non-polar, and lipid-soluble molecules can pass through easily. Large, charged, or polar molecules generally require transport proteins. Water molecules can pass through, albeit slowly, or via aquaporins. Amino acid-based hormones are typically large, polar molecules that cannot directly diffuse across the lipid bilayer and require specific receptors and signaling pathways.

• A. water molecules - Can pass (osmosis, aquaporins).
• B. non polar molecules - Can pass easily (e.g., O$_2$, CO$_2$).
• C. amino acid based hormones - Generally too large and/or polar to pass directly.
• D. fat-soluble molecules - Can pass easily (e.g., steroid hormones).

The correct option is C.

• C. amino acid based hormones

Question 9: An isotonic solution is one which

An isotonic solution has the same solute concentration (osmolarity) as the inside of a cell, such as a red blood cell. This results in no net movement of water across the cell membrane, and the cell maintains its normal shape and volume.

• A. has an osmotic pressure that is different to red blood cells - Incorrect, isotonic means same osmotic pressure.
• B. has an osmolarity less than that of red blood cells - Incorrect, this describes a hypotonic solution.
• C. causes no net movement of water between the solution and red blood cells - Correct, this is the definition of isotonic.
• D. has an osmolarity greater than that of red blood cells - Incorrect, this describes a hypertonic solution.

The correct option is C.

• C. causes no net movement of water between the solution and red blood cells

Question 10: One of the buffer systems in the blood is the carbonic acid/bicarbonate buffer. It helps to maintain the body's acid-base balance by destroying any excess:

The carbonic acid/bicarbonate buffer system works by neutralizing both excess hydrogen ions (acids) and excess hydroxide ions (bases) to maintain a stable pH. When there is an excess of acid, bicarbonate ions (HCO$_3^-$) bind to hydrogen ions (H$_+$) to form carbonic acid (H$_2$CO$_3$). When there is an excess of base, carbonic acid dissociates to release H$_+$ and neutralize the base. The question asks what it destroys any excess of, implying both acidic and basic components.

• A. Hydrogen ions in the blood - The buffer system neutralizes excess H$_+$.
• B. acid or base in the blood - This is a general statement that encompasses the function of a buffer system.
• C. Hydroxide ions formed in the blood - The buffer system neutralizes excess OH$_-$ by providing H$_+$.
• D. bicarbonate ions formed in the blood - Bicarbonate ions are part of the buffer system, not what it destroys.

While options A and C are specific components, option B provides a more complete description of what a buffer system, including the carbonic acid/bicarbonate buffer, handles to maintain balance. It destroys excess acid (H$_+$) or base (OH$_-$).

The correct option is B.

• B. acid or base in the blood

Question 11: The primary somatosensory cortex is located in the:

The primary somatosensory cortex is responsible for processing sensory information from the body, such as touch, temperature, pain, and pressure. It is located in the postcentral gyrus of the parietal lobe of the brain. The precentral gyrus, in contrast, contains the primary motor cortex.

• A. Precentral gyrus - This is the primary motor cortex.
• B. Postcentral gyrus - This is the primary somatosensory cortex.
• C. Frontal pole - Part of the frontal lobe, involved in higher cognitive functions.
• D. Temporal cortex - Involved in auditory processing, memory, and language.

The correct option is B.

• B. Postcentral gyrus

Question 12: Which of the following statements about the role of the kidneys or lungs in the maintenance of acid-base balance in the body is FALSE?

Let's evaluate each statement:

• A. The kidneys are able to affect several buffer systems but the lungs affect only one.
  • The lungs primarily regulate CO$_2$ (part of the carbonic acid buffer system). The kidneys can excrete H$_+$, reabsorb HCO$_3^-$, and produce new HCO$_3^-$, influencing the carbonic acid-bicarbonate system, phosphate buffer system, and ammonia buffer system. This statement is generally true.
• B. The lungs exert their influence on the carbonic acid/bicarbonate buffer system.
  • The lungs regulate the amount of CO$_2$ in the blood, which directly impacts the carbonic acid concentration (H$_2$CO$_3$) and thus the carbonic acid/bicarbonate buffer system. This statement is true.
• C. Neither the lungs nor the kidneys have much influence over the protein buffer.
  • Protein buffers are significant in both intracellular and extracellular fluids. While lungs and kidneys don't directly regulate protein synthesis, their control over overall blood pH (which they strongly influence) directly impacts the effectiveness and ionization state of protein buffers. Therefore, they do have an influence. This statement is false.
• D. The kidneys are able to respond more rapidly than the lungs to changes in acid-base balance.
  • The lungs can adjust ventilation rate within minutes to alter CO$_2$ levels and rapidly change pH. The kidneys, however, take hours to days to fully adjust their excretion and reabsorption of acids and bases. This statement is false.

Both C and D are false statements. However, in multiple-choice questions, there is usually only one best answer. Let's re-examine.
Statement C: "Neither the lungs nor the kidneys have much influence over the protein buffer." This is false because by regulating overall pH, they indirectly influence all buffer systems, including protein buffers.
Statement D: "The kidneys are able to respond more rapidly than the lungs to changes in acid-base balance." This is definitively false. Lungs are rapid, kidneys are slow. This is a fundamental concept in acid-base physiology.

Given the options, statement D is a more direct and unequivocally false statement regarding the speed of response, which is a key distinguishing feature between renal and respiratory compensation.

The correct option is D.

• D. The kidneys are able to respond more rapidly than the lungs to changes in acid-base balance.

Question 13: Choose one answer below that completes the sentence so that it makes a true statement: Positive feedback:

Let's analyze the given options for positive feedback:

• A. is the way the body maintains homeostasis
  • This statement is false. Homeostasis is primarily maintained by negative feedback mechanisms, which work to counteract changes and return the body to a set point. Positive feedback amplifies a change, moving the system further away from the set point.
• B. is a response that opposes a stimulus
  • This statement is false. This describes negative feedback. Positive feedback is a response that amplifies or enhances the original stimulus.

Based on the standard definitions of positive and negative feedback, neither option A nor option B correctly completes the sentence to make a true statement about positive feedback. Both options describe negative feedback or the general concept of homeostasis (which is mostly negative feedback). Without further options or clarification, it's not possible to select a correct answer from the choices provided.