Which of the following hormones regulates calcium levels in the blood?

Correct Answer: B

Rationale: The correct answer is B, Parathyroid hormone. Parathyroid hormone plays a crucial role in regulating calcium levels in the blood by increasing calcium levels when they are too low. This hormone acts on the bones, kidneys, and intestines to ensure proper calcium balance in the body. Insulin (choice A) is involved in glucose metabolism, not calcium regulation. Thyroid hormone (choice C) primarily regulates metabolism, and while it indirectly influences calcium levels, it is not the primary regulator. Glucagon (choice D) is involved in increasing blood glucose levels, not calcium regulation.

Correct Answer: B

Rationale: The correct answer is the larynx. The larynx, commonly referred to as the voice box, is responsible for voice production in the respiratory system. It contains vocal cords that vibrate to produce sound. The pharynx is a passage for food and air, the trachea is a tubular structure that carries air to and from the lungs, and the bronchi are the main airway passages in the lungs. Therefore, choices A, C, and D are incorrect as they do not play a direct role in voice production.

Correct Answer: B

Rationale: The correct answer is B, Nephron. The nephron is indeed the basic structural and functional unit of the kidney. It is responsible for filtering blood, regulating electrolytes, maintaining fluid balance, and removing waste products. Choice A, Neuron, is incorrect as neurons are nerve cells, not specific to kidney function. Choice C, Glomerulus, is a component of the nephron but not the entire functional unit. Choice D, Axon, is a part of nerve cells and is not related to kidney structure or function.

Correct Answer: B

Rationale: Fibrous joints connect the bones of the skull. These joints are immovable or provide very limited movement, providing stability and protection to the brain. Synovial joints (Choice A) are found in the limbs and allow for a wide range of movements. Cartilaginous joints (Choice C) are connected by cartilage and allow limited movement. Ball-and-socket joints (Choice D) allow for a wide range of motion, such as the hip and shoulder joints, but they do not connect the bones of the skull.

Correct Answer: B

Rationale: The correct answer is B: To transport oxygen and nutrients. The primary function of the circulatory system is to deliver oxygen and essential nutrients to cells throughout the body and remove waste products like carbon dioxide. Choice A is incorrect as regulating body temperature is primarily the function of the body's thermoregulatory system. Choice C is incorrect as fighting infection is mainly the role of the immune system. Choice D is incorrect as breaking down waste is primarily handled by the digestive system.