Correct Answer: A

Rationale: The correct answer is A: Kidneys. The kidneys play a crucial role in regulating the amount of sodium in the body. They achieve this by filtering blood and controlling the excretion or reabsorption of sodium. The small intestine is primarily responsible for nutrient absorption, not sodium regulation. The large intestine is mainly involved in water absorption and waste elimination, not sodium balance. The skin helps regulate body temperature through sweating and does not directly regulate sodium levels.

Correct Answer: D

Rationale: A decrease in blood protein concentration would lead to a reduction in osmotic pressure, which is responsible for drawing fluid back into the capillaries. This decrease in osmotic pressure would result in an increase in interstitial fluid volume as fluid moves out of the capillaries, and a decrease in blood plasma volume as less fluid is drawn back into the circulation. Therefore, the correct answer is to increase interstitial fluid volume and decrease blood plasma volume. Choices A, B, and C are incorrect because they do not reflect the impact of decreased blood protein concentration on fluid volumes.

Correct Answer: D

Rationale: Intracellular fluid contains phosphate ions and protein molecules as essential anions. Phosphate ions play a crucial role in various cellular processes, including energy transfer. Proteins, being large molecules with negative charges, also contribute significantly to the negative ion concentration within cells. Chlorine is primarily an extracellular anion and is not as prominent as phosphate ions and proteins within intracellular fluid, making it a less important negative ion in this context. Therefore, the correct answer is D because both phosphate ions and protein molecules are crucial negative ions in intracellular fluid.

Correct Answer: A

Rationale: The correct answer is A: Skin. After the kidneys, the skin is the second largest route of water loss through perspiration. Choice B, Lungs, is incorrect as the lungs primarily exchange gases and do not play a significant role in water loss. Choice C, Intestines, is also incorrect as water loss through the intestines is minimal since most water is reabsorbed during digestion. Choice D, Muscles, is incorrect as muscles are not a major source of water loss in the body.

Correct Answer: D

Rationale: The correct answer is D. The sources of water intake include drinking fluids, consuming water from the food we eat, and water from metabolic processes. Water intake is not solely from the liquids we drink but also from the water content present in the food we consume and the water produced during metabolic processes such as cellular respiration. Therefore, option D is the correct answer as it covers all the sources of water intake. Options A, B, and C alone do not encompass all the sources of water intake, making them incorrect choices.