Vitamin D is synthesized by ....in the presence of sunlight

Correct Answer: A

Rationale: The correct answer is A: Skin. Vitamin D is synthesized in the skin when it is exposed to sunlight. UV rays convert a form of cholesterol in the skin into Vitamin D. The liver and kidney play roles in converting and activating Vitamin D, but they are not where Vitamin D is initially synthesized. The stomach is not involved in the synthesis of Vitamin D. So, the skin is the correct choice for the synthesis of Vitamin D in the presence of sunlight.

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: 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: 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.