Which of the following is a positive feedback mechanism in the climate system?

Correct Answer: B

Rationale: Melting of polar ice reducing albedo is a positive feedback mechanism. Ice's high albedo (~0.6-0.9) reflects sunlight; melting exposes darker ocean/land (~0.1), absorbing more heat, accelerating warming and further melting amplifying climate change (e.g., Arctic amplification, ~2-3× global rate). Increased cloud cover (negative feedback) reflects sunlight (~50 W/m²), cooling Earth false. Vegetation growth absorbs CO2, mitigating warming (negative) false. Cooling oceans enhance CO2 solubility, reducing greenhouse effect (negative) false. Ice-albedo feedback's self-reinforcing loop, per climate models (e.g., IPCC), distinguishes it as positive, intensifying temperature rise, a critical dynamic in polar regions.

Correct Answer: B

Rationale: Simple cuboidal epithelium, a single layer of cube-shaped cells, is specialized for secretion and absorption. It lines thyroid gland follicles (B), where it secretes thyroid hormones, and other structures like kidney tubules. The intestine (A) has simple columnar epithelium for nutrient absorption, with taller cells and microvilli. The epidermis (C) is stratified squamous, designed for protection, not a single layer. The trachea (D) features pseudostratified columnar epithelium with cilia and goblet cells for mucus clearance. B is correct thyroid follicles match the description, unlike the others, which serve different functions requiring distinct epithelial types.

Correct Answer: D

Rationale: Red marrow (A) contains hematopoietic cells, producing blood cells. Yellow marrow (B) is mostly adipocytes, storing fat. Yellow can convert to red marrow (C) in anemia to boost hematopoiesis. Yellow marrow lacks significant hematopoietic cells (D), unlike red, making D false. Its fat-dominated composition contrasts with red marrow's active blood cell production, and while conversion occurs, yellow marrow itself doesn't house hematopoietic cells unless transformed, making D the exception.

Correct Answer: B

Rationale: Respiratory bronchioles are lined with simple cuboidal epithelium (B), transitioning from conducting airways' pseudostratified columnar (C) to alveoli's simple squamous (A). Simple columnar (D) is in intestines, not lungs. B is correct cuboidal cells with some cilia and club cells suit gas exchange initiation, unlike others.