Which vitamin is necessary for calcium absorption?

Correct Answer: C

Rationale: Vitamin D is essential for the absorption of calcium in the intestines, aiding in the maintenance of strong bones and teeth. It helps regulate calcium and phosphorus levels in the body, supporting bone health and preventing conditions like osteoporosis. Vitamin A (Choice A) is important for vision and immune function, not specifically for calcium absorption. Vitamin C (Choice B) is crucial for collagen synthesis and immune function but is not directly involved in calcium absorption. Vitamin K (Choice D) plays a role in blood clotting and bone health, but it is not primarily responsible for calcium absorption.

Correct Answer: B

Rationale: The main function of the endocrine system is to regulate various body functions by releasing hormones, which act as chemical messengers. These hormones help maintain homeostasis, regulate metabolism, growth, development, and other essential functions in the body. Option A is incorrect as fighting infections is primarily the role of the immune system, not the endocrine system. Option C is incorrect as the production of red blood cells mainly occurs in the bone marrow. Option D is incorrect as the transportation of oxygen is primarily carried out by the respiratory and circulatory systems. Therefore, option B is the correct answer as it accurately describes the primary role of the endocrine system.

Correct Answer: A

Rationale: The correct answer is A: "To transport oxygen and nutrients." The primary function of the cardiovascular system is to transport oxygen, nutrients, and hormones to cells throughout the body and remove waste products. This system plays a crucial role in maintaining homeostasis by delivering essential substances to tissues and organs while eliminating metabolic waste. Choices B, C, and D are incorrect because although the cardiovascular system indirectly helps in removing waste products through circulation, its primary function is focused on transporting essential substances and not on regulating body temperature or fighting infections.

Correct Answer: B

Rationale: The alveoli in the lungs are tiny air sacs responsible for the exchange of oxygen and carbon dioxide during breathing. Oxygen from inhaled air diffuses into the bloodstream through the alveoli, while carbon dioxide produced by cells is removed from the blood and exhaled out of the body through the alveoli. This gas exchange process is essential for the body to obtain oxygen and get rid of carbon dioxide, supporting cellular functions and maintaining overall health. Choices A, C, and D are incorrect because the alveoli do not filter blood, transport nutrients, or store oxygen. Their main function is gas exchange.

Correct Answer: A

Rationale: The correct answer is A: 'To filter waste from the blood.' The primary function of the kidneys in the urinary system is to filter waste products and excess substances from the blood, forming urine, which is then excreted from the body. This process helps maintain the body's internal environment by regulating the balance of electrolytes, fluid levels, and eliminating metabolic waste products. Choices B, C, and D are incorrect because while the kidneys do produce urine, regulate blood pressure, and maintain fluid balance, their primary function within the urinary system is the filtration of waste from the blood.