Endocrine glands differ from exocrine glands in that:

Correct Answer: A

Rationale: The correct answer is A because endocrine glands are ductless and release hormones directly into the bloodstream to reach target organs, while exocrine glands release their secretions through ducts onto the body's surface or into specific locations. This distinction is crucial as it highlights the mode of transportation of their secretions. Choices B, C, and D are incorrect because exocrine glands do not release waste; they release enzymes, sweat, etc. Exocrine glands can be formed by various types of tissues, not just connective tissue. Additionally, exocrine glands do not necessarily act completely independently; they can be part of a system or network but still release their secretions through ducts.

Correct Answer: B

Rationale: The correct answer is B: negative feedback system. In a negative feedback system, the body's response to a stimulus works to counteract the initial stimulus, bringing the body back to its set point. In the context of the question, hormone release stops when the stimulus is satisfied, which is characteristic of a negative feedback system. A: Positive feedback system amplifies the initial stimulus rather than counteracting it. C: Lock and key system refers to how enzymes bind to specific substrates, not related to hormone regulation. D: Solar system is unrelated to physiological processes.

Correct Answer: C

Rationale: The correct answer is C: Iodine. Iodine is essential for the production of thyroid hormones T3 and T4. These hormones regulate metabolism, growth, and development. Potassium (A), Sodium (B), and Calcium (D) do not play a direct role in thyroid function. Potassium and Sodium are electrolytes important for nerve function and fluid balance, while Calcium is crucial for bone health and muscle function. Therefore, the correct answer is Iodine as it is specifically required for normal thyroid function.

Correct Answer: D

Rationale: The correct answer is D: Both A & B. The thyroid and parathyroid glands work together to regulate calcium levels in the blood. The parathyroid gland releases parathyroid hormone, which increases calcium levels, while the thyroid gland secretes calcitonin, which decreases calcium levels. Therefore, both glands play a crucial role in maintaining calcium homeostasis. Choice A, the thyroid gland, is incorrect as it primarily regulates metabolism. Choice C, the adrenal medulla, is incorrect as it is responsible for releasing adrenaline and noradrenaline, not regulating calcium levels.

Correct Answer: B

Rationale: The correct answer is B: Weight gain. Addison's disease is characterized by adrenal insufficiency, leading to symptoms such as salt craving, hypoglycemia, and hyperpigmentation due to increased melanin production. Weight loss, not weight gain, is commonly associated with Addison's disease due to decreased cortisol levels. Salt craving is due to sodium loss, hypoglycemia results from insufficient cortisol levels, and hyperpigmentation is caused by elevated ACTH levels stimulating melanin production. Weight gain is not a typical symptom, making it the correct answer.