What is the primary function of the respiratory system?

Correct Answer: A

Rationale: The primary function of the respiratory system is to facilitate the exchange of oxygen and carbon dioxide between the air and the bloodstream. Oxygen is taken in during inhalation and transported to cells, while carbon dioxide is removed during exhalation as a waste product of cellular metabolism. Choices B, C, and D are incorrect as they do not reflect the primary function of the respiratory system. Regulating body temperature is mainly controlled by the thermoregulatory system, fighting infections is a function of the immune system, and producing energy is primarily done by the metabolic system.

Correct Answer: B

Rationale: Epithelial tissue is the correct answer. It forms the outer layer of the skin, serving as a protective barrier against pathogens and environmental damage. This tissue type is essential for maintaining skin integrity and plays a crucial role in skin function. Connective tissue (Choice A), although important for providing support and structure, does not form the outer layer of the skin. Muscle tissue (Choice C) is responsible for movement and is not the primary tissue in the skin. Nervous tissue (Choice D) is involved in transmitting signals but is not the main component of the skin's outer layer.

Correct Answer: C

Rationale: The thyroid gland is responsible for regulating metabolism. It produces hormones such as thyroxine, which plays a key role in influencing the body's metabolic rate. The pituitary gland is known as the 'master gland' but is not directly responsible for regulating metabolism. The adrenal gland is involved in the stress response and producing hormones like cortisol, not primarily regulating metabolism. The pineal gland produces melatonin, which regulates sleep-wake cycles, not metabolism. Therefore, the correct answer is the thyroid gland.

Correct Answer: B

Rationale: Vitamin C is essential for the synthesis of collagen, a crucial protein that plays a significant role in maintaining the structural integrity of skin, blood vessels, and bones. Collagen is responsible for the strength, elasticity, and firmness of these tissues. Without sufficient vitamin C, the body cannot form collagen properly, leading to various health issues like scurvy, impaired wound healing, and fragile blood vessels. Choices A, C, and D are incorrect. Vitamin A plays a role in vision, immune function, and skin health. Vitamin D is crucial for bone health and immune function, while Vitamin E is an antioxidant that helps protect cells from damage.

Correct Answer: B

Rationale: The pineal gland secretes melatonin, a hormone that plays a crucial role in regulating the sleep-wake cycle. Melatonin production is influenced by exposure to light, with levels increasing in the evening to promote sleep and decreasing in the morning to signal wakefulness. Choices A, C, and D are incorrect because the thyroid gland primarily regulates metabolism, the adrenal gland produces hormones like adrenaline and cortisol related to stress response, and the pituitary gland controls various functions by releasing different hormones but not specifically related to regulating sleep.