What is the main function of the endocrine system?

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: B

Rationale: The correct function of the lungs in the respiratory system is to exchange gases. The lungs facilitate the exchange of oxygen and carbon dioxide between the air we breathe in and the blood, ensuring oxygen is absorbed and carbon dioxide is removed during respiration. Choice A is incorrect as the kidneys, not the lungs, filter blood. Choice C is incorrect as energy production primarily occurs in cells, not in the lungs. Choice D is incorrect as waste removal, such as the excretion of carbon dioxide, is a function of the lungs, but the primary function is the exchange of gases.

Correct Answer: B

Rationale: The primary function of the respiratory system is to facilitate the exchange of gases. It transports oxygen from the air into the bloodstream, which is crucial for cellular respiration and providing energy to the cells. Additionally, it removes carbon dioxide, which is a waste product that needs to be eliminated. Choices A, C, and D are incorrect because while the respiratory system does remove carbon dioxide, its primary role is oxygen transport, not nutrient delivery, sound, or speech production.

Correct Answer: B

Rationale: The small intestine is the primary site for nutrient absorption in the digestive system. It is responsible for absorbing nutrients from the digested food into the bloodstream for distribution throughout the body. Therefore, the correct function of the small intestine is to absorb nutrients. Choice A is incorrect because the gallbladder stores bile, not the small intestine. Choice C is incorrect because the digestion process primarily occurs in the stomach and small intestine. Choice D is incorrect because while the small intestine does play a role in enzyme production, its primary function is nutrient absorption.

Correct Answer: B

Rationale: The primary function of the skin is to protect the body from external damage. While the skin also helps regulate body temperature and produces vitamin D in response to sunlight, its main role is to act as a barrier against harmful external factors, such as pathogens and physical injuries. Choices A, C, and D are incorrect because although the skin does play a role in regulating body temperature and producing vitamin D, its primary function is providing protection against external threats.

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: A

Rationale: The glomerulus is the correct answer. It is a vital structure in the kidney responsible for filtering blood. The glomerulus is a network of capillaries that filters waste products and excess substances from the blood to form urine. While the Bowman's capsule, Loop of Henle, and Collecting duct are also essential components of the nephron, the primary site of blood filtration occurs at the glomerulus. The Bowman's capsule surrounds the glomerulus and collects the filtered fluid, the Loop of Henle reabsorbs water and important ions, and the Collecting duct further concentrates the urine, but none of these structures are primarily responsible for filtering blood as the glomerulus is.

Correct Answer: A

Rationale: The correct answer is Vitamin C. Vitamin C is essential for the absorption of iron, especially from plant-based sources. It aids in converting non-heme iron (found in plants) into a form that is easier for the body to absorb. This is crucial in preventing iron-deficiency anemia, making Vitamin C a key nutrient for overall health. Vitamin D (choice B) is important for calcium absorption and bone health, not iron absorption. Vitamin K (choice C) plays a role in blood clotting and bone metabolism, not iron absorption. Vitamin B12 (choice D) is important for red blood cell formation and neurological function but is not directly involved in iron absorption.

Correct Answer: A

Rationale: The correct answer is the Pineal gland. The pineal gland is responsible for producing melatonin, a hormone that helps regulate the sleep-wake cycle. Melatonin secretion is influenced by light exposure. Higher levels are observed at night to promote sleep, while lower levels during the day encourage wakefulness. Choices B, C, and D are incorrect as they are not associated with the production of melatonin. The thyroid gland produces hormones like thyroxine and triiodothyronine, the pituitary gland controls various other glands, and the adrenal gland produces hormones like adrenaline and cortisol.