Metachrosis is

Correct Answer: A

Rationale: Rationale: 1. Metachrosis refers to the ability of amphibians to change the intensity of their skin color. 2. Amphibians use metachrosis for camouflage, communication, and temperature regulation. 3. This process is not about shedding skin (B), thermoregulation (C), or metamorphosis (D). Summary of Incorrect Choices: B: Incorrect as metachrosis is about changing skin color, not shedding stratum corneum. C: Incorrect as metachrosis is not directly related to thermoregulation. D: Incorrect as metachrosis does not involve the transformation from larva to adult, which is metamorphosis.

Correct Answer: D

Rationale: The correct answer is D: Stratum germinativum. This layer is also known as the stratum basale and is the innermost layer of the epidermis where cell division and renewal occur. It contains stem cells that continuously divide to produce new keratinocytes. The other choices, A: Stratum granulosum, B: Stratum lucidum, and C: Stratum spinosum are all layers of the epidermis, but they are not the innermost layer where cell division primarily takes place.

Correct Answer: A

Rationale: The correct answer is A: Hyponychium. The hyponychium is the layer of stratum corneum located just under the free-edge of the nail. It serves as a protective barrier to prevent microorganisms from entering the nail bed. The lunula (B) is the white, crescent-shaped area at the base of the nail. The eponychium (C) is the cuticle that covers the base of the nail. The nail root (D) is the part of the nail embedded in the skin. Therefore, the hyponychium is the most appropriate answer as it specifically refers to the stratum corneum under the free-edge of the nail.

Correct Answer: D

Rationale: The correct answer is D: Melanin. Melanin is a pigment produced by skin cells in response to UV exposure, acting as a natural defense mechanism to protect the skin from sun damage. Collagen (A) is responsible for skin firmness, not skin darkening. Carotene (B) is a pigment found in certain foods like carrots but does not directly contribute to skin darkening. Keratin (C) is a protein that provides structure to the skin, hair, and nails, but it does not play a role in skin darkening. Therefore, the production of melanin is specifically increased in response to UV light exposure, making it the correct choice.

Correct Answer: D

Rationale: The correct answer is D: Hair papilla. The hair papilla is a small connective tissue peg located at the base of the hair follicle and contains nerve endings and blood vessels. It supplies nutrients to the hair bulb and helps in hair growth. The other choices are incorrect because: A) Hair cuticle is the outermost layer of the hair shaft. B) Hair bulb is the rounded, enlarged area at the base of the hair follicle where hair growth occurs. C) Hair matrix is the actively dividing part of the hair follicle responsible for producing new hair cells.