Keratin found in the skin rabbit is

Correct Answer: D

Rationale: Keratin found in rabbit skin is classified as a scleroprotein, which is a type of structural protein. Keratin is known for its tough and fibrous nature, providing strength and protection to the skin. Scleroproteins are characterized by their high tensile strength and are commonly found in structural tissues like skin, hair, and nails. Lipoproteins consist of lipids and proteins, glycoproteins have carbohydrate groups attached to the protein, and mucoproteins contain mucopolysaccharides. These types of proteins do not accurately describe the composition and function of keratin in rabbit skin.

Correct Answer: D

Rationale: Step 1: When a bird is transferred to a colder environment (10ºC), its body temperature tends to drop. Step 2: To maintain its body temperature, the bird needs to conserve and produce more heat internally. Step 3: This increased conservation and production of heat help the bird to keep its body temperature at the original constant level. Step 4: Therefore, option D is correct as it accurately describes the physiological response of a bird to a decrease in environmental temperature. Summary: Option A is incorrect because dissipation of heat does not maintain the body temperature but rather leads to a decline. Option B is incorrect as it suggests a decline without considering the bird's ability to regulate its temperature. Option C is incorrect as increased production and conservation of heat would not result in a rise above normal body temperature in response to a colder environment.

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.