Which of the following statements accurately describes vitamins?
Vitamins are inorganic substances that cannot be synthesized by animals.
Vitamins are inorganic substances that can be synthesized by animals.
Vitamins are organic substances that are mostly unable to be synthesized by animals.
Vitamins are organic substances that are mostly able to be synthesized by animals.
Vitamins are organic compounds that are essential for various physiological functions, but most animals cannot synthesize them endogenously. Therefore, they need to obtain vitamins from external sources such as diet. While some animals can synthesize certain vitamins to some extent, the statement "mostly unable to be synthesized by animals" reflects the general rule for most vitamins. Hence, the correct answer is option 3.