Haemoglobin is the main buffer for which of the following?

Correct Answer: C

Rationale: Haemoglobin is the main buffer for O2. It binds to oxygen in the lungs and releases it in tissues. This buffering action helps maintain a stable oxygen-carrying capacity in the blood. Choices A, B, and D are incorrect as haemoglobin does not primarily buffer PO3-, CO4^2-, or NO. These molecules do not have a direct relationship with haemoglobin's oxygen-carrying function.

Correct Answer: A

Rationale: Metabolic acidosis occurs when the body produces too much acid or fails to remove enough acid. Aspirin poisoning can lead to metabolic acidosis by increasing the production of lactic acid and impairing the kidney's ability to excrete acid. Severe vomiting and severe diarrhea can cause metabolic alkalosis due to loss of stomach acid or bicarbonate, respectively. Emphysema is associated with respiratory acidosis due to impaired gas exchange, not metabolic acidosis. Therefore, the correct answer is A (aspirin poisoning).

Correct Answer: D

Rationale: The correct answer is D (15/10). This ratio represents a decrease in bicarbonate (HCO3-) and an increase in carbonic acid (H2CO3), which indicates a respiratory acidosis condition. In respiratory acidosis, there is an accumulation of carbon dioxide (CO2) leading to increased carbonic acid formation. The other choices are incorrect because they do not reflect the appropriate changes in HCO3- and CO2 levels corresponding to respiratory acidosis. Choice A (40/1) and B (20/2) indicate alkalosis conditions with higher HCO3- levels, while choice C (20/5) suggests a normal ratio not reflective of an acid-base disorder.

Correct Answer: A

Rationale: Step 1: When the body synthesizes a more complex molecule, it often involves a series of chemical reactions that lead to the formation of the new molecule. Step 2: These reactions are typically energy-consuming and involve changes in molecular structures that cannot be easily reversed. Step 3: Once a substance is used in these irreversible reactions to form a more complex molecule, it cannot be restored to its original form. Step 4: Therefore, the statement that the process is irreversible and the original substance cannot be restored is true. Summary: Choice A is correct because the process of synthesizing a more complex molecule in the body involves irreversible reactions that permanently change the original substance. Choices B, C, and D are incorrect as they do not accurately describe the irreversible nature of this process.

Correct Answer: B

Rationale: The correct answer is B: FALSE. Extracellular fluid does not compose the majority of all the fluid in the body. Intracellular fluid actually makes up the majority of the body's fluid. This is because intracellular fluid is contained within the cells, while extracellular fluid is found outside the cells. Other choices (A, C, D) are incorrect as they do not accurately reflect the composition of body fluids.