The layer of stem cells that constantly divide to renew the epidermis is the

Correct Answer: A

Rationale: The correct answer is A: Stratum germinativum. This layer of stem cells constantly divides to renew the epidermis. The stratum germinativum is also known as the basal layer and is located at the bottom of the epidermis. It contains actively dividing cells responsible for producing new skin cells. The basal lamina (B) is a structure that separates the epidermis from the dermis but does not contain dividing stem cells. The stratum corneum (C) is the outermost layer of the epidermis composed of dead skin cells. The stratum granulosum (D) is a layer of the epidermis where cells begin to flatten and lose their nuclei, but it is not where active cell division occurs.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Melanin increases in concentration during sun exposure to protect the skin. 2. Option A is incorrect as melanin actually increases in concentration to protect against UV radiation. 3. Melanin is typically brown or black (B), released through melanosomes (C), and protects DNA from UV damage (D). 4. In summary, option A is the correct answer because melanin does not decrease in concentration during sun exposure; it increases to provide protection.

Correct Answer: D

Rationale: In thin skin, the epidermis contains 4 layers: stratum basale, spinosum, granulosum, and corneum. In thick skin, it contains an additional layer called stratum lucidum. Therefore, the correct answer is D. Option A is incorrect because thin skin has 4 layers. Option B is incorrect as thick skin has 5 layers. Option C is incorrect as thin skin has 4 layers and thick skin has 5 layers.

Correct Answer: B

Rationale: The correct answer is B: on the palms of the hands. This is because the palms of the hands have the highest concentration of merocrine sweat glands, which are responsible for regulating body temperature by producing sweat. The palms have a higher density of these glands compared to other areas listed in the choices. A: The chest does have sweat glands, but not the highest concentration compared to the palms. C: While the axillae (armpits) have a high concentration of apocrine sweat glands, merocrine glands are more abundant on the palms. D: The upper back also contains sweat glands, but not as densely packed as on the palms. In summary, the palms of the hands have the highest concentration of merocrine sweat glands, making them the correct choice.

Correct Answer: C

Rationale: The correct answer is C: apocrine sweat glands. These glands in the axilla become active at puberty due to hormonal changes, secreting a thick, odorless substance. Sebaceous glands produce oil, ceruminous glands produce earwax, and axillary glands are not a specific type of gland. Therefore, choice C is correct as it accurately describes the glands in the axilla that are activated during puberty.