Why vitamins are required in the diet — best general statement about biosynthetic capacity and quantitative need in humans.

Introduction / Context:
Vitamins are organic micronutrients required in small amounts for normal metabolism. The core reason they must be supplied by diet varies by vitamin and organism.

Given Data / Assumptions:

• Some vitamins cannot be synthesized at all by humans (e.g., vitamin C), others are synthesized insufficiently (e.g., niacin from tryptophan in limited amounts).
• Physiological demand exceeds endogenous production for many vitamins.

Concept / Approach:
The most accurate generalization is that endogenous synthesis is absent or inadequate for meeting needs; therefore, dietary intake is essential.

Step-by-Step Solution:
Evaluate absolute vs limited synthesis scenarios across vitamins.Recognize “inadequate amounts” captures both none and insufficient production cases.Select the statement that encompasses all vitamins broadly.Choose option c.

Verification / Alternative check:
Nutrition guidelines recommend dietary intake despite partial synthesis for certain vitamins (e.g., niacin, vitamin D via skin under sunlight) due to variability and insufficiency.

Why Other Options Are Wrong:
“Cannot synthesize at all” is too absolute; “partial synthesis” is too narrow; “none of the above” is incorrect; health-only need is false.

Common Pitfalls:
Overgeneralizing from a single vitamin to all vitamins.

Final Answer:
Organisms cannot synthesize these compounds in adequate amounts to meet physiological demand.