Carotenoids and provitamin A — which organisms biosynthesize β-carotene (along with α-carotene, γ-carotene, and cryptoxanthin)?

Introduction / Context:
β-Carotene and related carotenoids are provitamin A compounds that can be cleaved to retinal in animals. The site of their biosynthesis clarifies dietary sources and metabolic conversion.

Given Data / Assumptions:

• Plants (and many algae/microbes) synthesize carotenoids via the isoprenoid pathway.
• Animals do not synthesize β-carotene de novo; they obtain it from diet and convert it to retinoids.

Concept / Approach:
Identify primary producers in the food chain for these pigments: photosynthetic organisms and some microbes.

Step-by-Step Solution:
Exclude animals as de novo carotenoid producers.Recognize plants as canonical sources of β-carotene in foods (e.g., carrots, leafy greens).Select “Plants.”Note: Some bacteria/algae also synthesize carotenoids, but the option set asks to choose between “plants,” “animals,” etc.

Verification / Alternative check:
Food composition data show plant-based foods rich in β-carotene and cryptoxanthin; animal tissues contain retinoids accumulated from diet.

Why Other Options Are Wrong:
Animals do not make β-carotene; “both” is inaccurate; “none” is false; “only bacteria” excludes plants.

Common Pitfalls:
Confusing biosynthesis with bioconversion of carotenoids to retinoids in animals.

Final Answer:
Plants.