What is the main function of the immune system?

Correct Answer: B

Rationale: The main function of the immune system is to protect the body from infections by identifying and destroying pathogens like bacteria and viruses. It plays a crucial role in maintaining overall health and preventing illnesses. Choice A is incorrect because hormone production is primarily handled by the endocrine system, not the immune system. Choice C is incorrect as waste removal is mainly performed by the excretory system, not the immune system. Choice D is incorrect as regulating body temperature is primarily the role of the thermoregulatory system, not the immune system.

Correct Answer: B

Rationale: Adrenaline, also known as epinephrine, is released by the adrenal glands during stress to prepare the body for rapid action. It helps in triggering the body's fight-or-flight response, increasing heart rate, and providing a burst of energy when faced with stressful situations. Insulin (Choice A) is produced by the pancreas to regulate blood sugar levels, not by the adrenal glands. Melatonin (Choice C) is a hormone that regulates sleep-wake cycles and is produced by the pineal gland, not the adrenal glands. Cortisol (Choice D) is another hormone produced by the adrenal glands, but it is not the primary hormone released during immediate stress responses; it is more involved in long-term stress regulation.

Correct Answer: B

Rationale: The correct answer is B, Nucleus. The nucleus is the organelle in the cell that contains the genetic material (DNA). DNA within the nucleus determines the cell's functions and characteristics, making it essential for cell function and replication. Choice A, Ribosome, is responsible for protein synthesis, not genetic material storage. Choice C, Mitochondria, produces energy but does not contain the genetic material. Choice D, Endoplasmic reticulum, is involved in protein synthesis and lipid metabolism but does not house the genetic material.

Correct Answer: A

Rationale: The spleen plays a crucial role in the immune system by filtering blood, specifically removing old or damaged red blood cells. It also stores lymphocytes, which are white blood cells that help fight infections. While the spleen does not produce white blood cells or antibodies, its main functions lie in blood filtration and storage of immune cells. Therefore, the correct answer is A. Choice B is incorrect because the spleen does not produce white blood cells. Choice C is incorrect as the spleen stores lymphocytes but does not primarily function to do so. Choice D is incorrect because the spleen does not produce antibodies.

Correct Answer: B

Rationale: The correct answer is B: Melatonin. Melatonin, produced by the pineal gland, is the hormone involved in regulating the sleep-wake cycle. It plays a crucial role in signaling the body that it is time to sleep and is influenced by light exposure. Melatonin levels typically rise in the evening, promoting sleep, and decrease in the morning, helping in waking up. Choice A, Insulin, is involved in regulating blood sugar levels, not the sleep-wake cycle. Choice C, Cortisol, is a stress hormone that helps regulate metabolism and immune response but is not primarily involved in the sleep-wake cycle. Choice D, Thyroxine, is a hormone produced by the thyroid gland that regulates metabolism, growth, and development, but it is not directly involved in regulating the sleep-wake cycle.