What is the name for the sac-shaped structures in which carbon dioxide and oxygen exchange takes place?

Correct Answer: C

Rationale: The alveoli are the tiny sac-shaped structures in the lungs where gas exchange occurs. Oxygen from the air we breathe diffuses into the bloodstream through the alveoli, while carbon dioxide, a waste product produced by cells, is removed from the blood and exhaled out of the body through the alveoli. Choices A, B, and D are incorrect. Kidneys are organs responsible for filtering waste from the blood, the medulla oblongata is a part of the brain responsible for autonomic functions, and bronchioles are smaller airway passages in the lungs that branch off from the bronchi.

Correct Answer: A

Rationale: The correct answer is the sinoatrial node. This node, also referred to as the pacemaker of the heart, is responsible for initiating the electrical impulses that stimulate cardiac muscle contractions. It plays a crucial role in setting the pace and rhythm of the heart's contractions. Choices B, C, and D (the left ventricle, the aorta, and the tricuspid valve, respectively) do not serve as the primary electrical stimulator of the cardiac muscle. While the left ventricle is a chamber of the heart that pumps oxygenated blood to the body, the aorta is the main artery that carries blood away from the heart, and the tricuspid valve is a one-way valve that ensures blood flows properly through the heart, none of these structures initiate the electrical impulses that cause the cardiac muscle to contract.

Correct Answer: D

Rationale: The correct answer is D. The primary function of the endocrine system is to maintain homeostasis. Homeostasis refers to the stable internal conditions of the body, including body temperature, blood pH, and glucose levels. The endocrine system achieves this by releasing hormones that regulate various physiological processes and help keep the body's internal environment in balance. Choices A, B, and C are incorrect because while the endocrine system does influence heart rate, electrolyte and water balance, and respiration to some extent, its primary role is to regulate homeostasis by releasing hormones.

Correct Answer: C

Rationale: The pancreas is the correct answer as it functions as both an endocrine and exocrine gland. The endocrine function involves secreting insulin and glucagon into the bloodstream to regulate blood sugar levels, while the exocrine function involves releasing digestive enzymes into the small intestine to aid in digestion. The kidney (Choice A) primarily functions in the excretory system by filtering blood and producing urine. The spleen (Choice B) is involved in the immune system and blood storage but does not have endocrine or exocrine functions. The stomach (Choice D) is mainly an organ of the digestive system, secreting gastric juices to aid in digestion, but it does not have a dual endocrine and exocrine function like the pancreas.

Correct Answer: B

Rationale: To calculate the grams of solid CaCO3 needed for a 0.35 M solution, we first find the molar mass of CaCO3: Ca = 40.07 g/mol, C = 12.01 g/mol, O = 15.99 g/mol. The molar mass of CaCO3 is 40.07 + 12.01 + (3 * 15.99) = 100.08 g/mol. The molarity formula is Molarity (M) = moles of solute / liters of solution. Since we have 0.35 moles/L and 600 mL = 0.6 L, we have 0.35 mol/L * 0.6 L = 0.21 moles of CaCO3 needed. Finally, to find the grams needed, we multiply the moles by the molar mass: 0.21 moles * 100.08 g/mol = 21.01 g, which rounds to 19.7 g. Therefore, 19.7 grams of solid CaCO3 are needed to make 600 mL of a 0.35 M solution. Choice A (18.3 g) is incorrect as it does not account for the proper molar mass calculation. Choice C (21.0 g) and Choice D (24.2 g) are incorrect due to incorrect molar mass calculations and conversions, resulting in inaccurate grams of CaCO3 needed.