Correct Answer: A

Rationale: The correct answer is A: Ectoderm. The nervous system develops from the ectoderm, which is the outermost of the three germ layers. The ectoderm gives rise to structures such as the skin, hair, nails, and the entire nervous system. Choices B, C, and D are incorrect because the endoderm gives rise to the lining of the gut and associated organs, the gastroderm is not a recognized germ layer, and the mesoderm forms structures like muscles, bones, blood, and the circulatory system, but not the nervous system.

Correct Answer: A

Rationale: Insulin is the hormone responsible for regulating blood sugar levels by facilitating the uptake of glucose into cells. Insulin helps lower blood sugar levels by promoting the storage of glucose in the liver, muscle, and fat cells. Adrenaline, cortisol, and melatonin do not directly regulate blood sugar levels. Adrenaline is involved in the fight-or-flight response, cortisol is a stress hormone that affects metabolism, immune response, and anti-inflammatory actions, while melatonin regulates sleep-wake cycles.

Correct Answer: B

Rationale: White blood cells play a crucial role in the immune system by fighting infection and protecting the body from foreign invaders. Choice A, 'To transport oxygen,' is incorrect because red blood cells are responsible for transporting oxygen. Choice C, 'To carry oxygen,' is also inaccurate for the same reason. Choice D, 'To produce antibodies,' while related to the immune system, is not the primary function of white blood cells, as their main role is to directly combat infections.

Correct Answer: B

Rationale: The correct answer is B: Sebaceous gland. Sebaceous glands are responsible for producing oil (sebum) that keeps the skin and hair moisturized. Sudoriferous glands produce sweat, not oil, and are involved in temperature regulation. Hair follicles are responsible for hair growth and do not produce oil directly. Melanocytes are cells responsible for producing melanin, the pigment that gives skin its color, and are not involved in oil production.

Correct Answer: A

Rationale: The correct answer is A, mediastinum. The mediastinum is the space between the lungs in the chest that contains the heart, major blood vessels, esophagus, trachea, and other structures. This area separates the lungs into right and left cavities. Choice B, pericardial cavity, is incorrect as it refers to the space that surrounds the heart. Choice C, pleural cavity, is not the correct answer as it is the space between the layers of the pleura surrounding each lung. Choice D, thoracic space, is a vague term and not specific to the space between the lungs.