Question

chromophore that gives our skin its color. uva waves activate melanin already present in our skin, causing our skin to tan quickly. uvb waves cause skin cells to produce more melanin, slowly tanning our skin over a few days.
our epidermis also contains the chromophore 7 - dehydrocholesterol (7 - dhc). 7 - dhc can be converted into vitamin d3 when it absorbs certain wavelengths of uvb waves. vitamin d3 is an essential nutrient for healthy bones and muscles.
the amount of vitamin d3 our skin produces depends in part on how long we stay in the sun, the time of day, the season, and the weather. most people in the united states do not spend enough time in the sun to produce all the vitamin d3 they need. however, foods like salmon and egg yolks can provide additional vitamin d3.
select the true statements.

• vitamin d3 is necessary for strong bones.
• vitamin d3 is produced in the middle layer of skin.
• vitamin d3 is produced when 7 - dehydrocholesterol absorbs uva waves.
• sun exposure is the only way people can get vitamin d3.

Explanation:

• The text states "Vitamin D3 is an essential nutrient for healthy bones and muscles", which supports the first statement.
• The epidermis (outer layer) contains 7 - DHC that converts to Vitamin D3 (not the middle layer), so the second statement is false.
• 7 - DHC converts to Vitamin D3 when it absorbs UVB waves (not UVA), so the third statement is false.
• The text mentions foods like salmon and egg yolks can provide additional Vitamin D3, so sun exposure is not the only way, making the fourth statement false.

Answer:

Vitamin D3 is necessary for strong bones.