When a bird is transferred from 30ºC to 10ºC, its body temperature-

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: 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.

Correct Answer: A

Rationale: Step 1: Cyanosis is a bluish discoloration of the skin due to insufficient oxygen in the blood. Step 2: Oxygen-starved blood appears bluish as it reflects less red light. Step 3: Therefore, cyanosis signifies a lack of oxygen in the blood, not related to sun exposure. Summary: Choice A is correct as it accurately reflects the physiological cause of cyanosis. Choices B, C, and D are incorrect as they do not relate to the underlying mechanism of cyanosis.