Each of the following is a function of vitamin A, except one. Which is the exception?

Correct Answer: C

Rationale: The correct answer is C. Maintenance of more than 200 genes is not a function of vitamin A; instead, it is a function of Vitamin D. Vitamin A plays a crucial role in the prevention of night blindness by aiding in the production of the visual pigment rhodopsin. It also supports the growth of soft tissues and bone, as well as the integrity of body openings and their linings. Choice C is incorrect because the maintenance of genes is primarily associated with Vitamin D, not Vitamin A.

Correct Answer: C

Rationale: While UV radiation can penetrate uncovered skin and convert a precursor of vitamin D to vitamin D3, sunscreen does block the formation of vitamin D3. Sunscreen is recommended by dermatologists to prevent sunburn and reduce the risk of skin cancer. The other choices are correct: the body can produce sufficient vitamin D from sunlight, UV radiation can convert a precursor of vitamin D to vitamin D3, and skin generally produces less vitamin D as a person ages.

Correct Answer: B

Rationale: Tocopherol, Choice B, is not a form of vitamin K; it is another name for vitamin E. Phylloquinone (Choice A), menaquinone (Choice C), and menadione (Choice D) are all forms of vitamin K. Phylloquinone is vitamin K1 found in green plants, menaquinone is vitamin K2 produced in the large intestine and found in animal tissues, and menadione is a synthetic form of vitamin K. Therefore, Choice B is the correct answer because it does not belong to the vitamin K group, unlike the other options.

Correct Answer: D

Rationale: The correct answer is D. Vitamin K absorption decreases with high levels of vitamin E supplementation because in larger amounts, vitamin E acts as an anticoagulant. Vitamin K is not produced in the gut but can be obtained from food sources or supplements. Vitamin K is essential for the synthesis of blood-clotting factors and is crucial in maintaining prothrombin levels, which is vital for proper blood clotting. The incorrect choice, D, is misleading as high levels of vitamin E supplementation hinder vitamin K absorption due to its anticoagulant properties. Dental hygienists should be aware of the importance of vitamin K in blood clotting, especially when treating patients who are on anticoagulant medications for conditions like stroke prevention.

Correct Answer: C

Rationale: Vitamin C plays a crucial role in protecting the integrity of cellular membranes. It is essential for collagen synthesis, which is important for wound healing and maintaining skin, blood vessels, and other tissues. Choice A is incorrect as the transcription of DNA to RNA is facilitated by vitamin A. Choice B is incorrect as calcium absorption and regulation are functions of vitamin D. Choice D is incorrect as vitamin K serves as a catalyst for the synthesis of blood-clotting factors, not vitamin C.