The nails, claws, horns and hooves in mammals are produced by-

Correct Answer: D

Rationale: The correct answer is D: Stratum corneum of the skin. Nails, claws, horns, and hooves in mammals are produced by keratinized structures in the epidermis called the stratum corneum. This specialized layer of the skin is responsible for forming these protective structures. Cartilage (A) is not involved in the production of these structures. Bone (B) is part of the skeletal system and not directly responsible for the formation of nails, claws, horns, or hooves. Muscles of the skin (C) are involved in movement and expression but do not produce these particular structures. Therefore, the correct answer is D as it directly relates to the formation of nails, claws, horns, and hooves in mammals.

Correct Answer: B

Rationale: The correct answer is B: Stratum lucidum. Eleidin is a protein-rich substance found in the stratum lucidum, the clear layer of the epidermis located between the stratum corneum and stratum granulosum. This layer is characterized by its translucent appearance due to the presence of eleidin, which helps to provide waterproofing and protection to the skin. The stratum germinativum (A) is responsible for cell proliferation, the stratum granulosum (C) is where keratinocytes undergo apoptosis, and the stratum corneum (D) consists of dead keratinocytes and serves as a barrier to external factors.

Correct Answer: A

Rationale: The correct answer is A: 5. The thorn penetrated through the sole of Joe's foot to the dermis. The epidermis has 5 layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. As the thorn reached the dermis, it had to pass through all 5 layers of the epidermis. Therefore, the correct answer is 5. Summary: B: 2 - Incorrect, not enough layers penetrated. C: 0 - Incorrect, the thorn penetrated the epidermis. D: 4 - Incorrect, the thorn penetrated all 5 layers of the epidermis.

Correct Answer: D

Rationale: The correct answer is D: The blood flow to the skin increases. When a fair-skinned person is sunburned, the body increases blood flow to the affected area to help with healing. This increased blood flow causes the skin to appear red due to the dilation of blood vessels near the skin surface. Choices A, B, and C are incorrect because a decrease in blood supply, an increase in red melanocytes, or an increase in production of red pigments do not directly explain why the skin turns red after sunburn.

Correct Answer: D

Rationale: The correct answer is D: sebaceous gland. Sebaceous glands are holocrine glands, where entire cells are released with their secretions. The sebaceous glands produce sebum by the disintegration of entire cells, a characteristic of holocrine secretion. A: Merocrine glands release secretions through exocytosis, not by disintegration of cells. B: Ceruminous glands produce earwax and are classified as modified apocrine glands. C: Apocrine glands release secretions along with a part of the cell cytoplasm, not the entire cell.