Cellular energy supply in eukaryotes Which organelles are primarily responsible for supplying usable chemical energy (ATP) in eukaryotic cells?

Introduction / Context:
Energy metabolism is central to cell biology. In eukaryotes, ATP is produced predominantly by oxidative phosphorylation in mitochondria and, in photosynthetic organisms, by photophosphorylation in chloroplasts. Understanding which organelles perform these processes clarifies how cells power biosynthesis, movement, and homeostasis across diverse tissues and species.

Given Data / Assumptions:

• Eukaryotic cells may be animal, fungal, plant, or protist.
• Photosynthetic eukaryotes contain chloroplasts; non-photosynthetic eukaryotes do not.
• ATP can be generated by substrate-level phosphorylation in the cytosol, but bulk ATP comes from organelle-based chemiosmosis.

Concept / Approach:
Mitochondria generate ATP via an electron transport chain that pumps protons to create a proton-motive force used by ATP synthase. Chloroplasts capture light energy to drive electron transfer and proton translocation across thylakoid membranes, also powering ATP synthase. Both organelles employ chemiosmotic coupling, though with different primary energy inputs (nutrient oxidation vs light).

Step-by-Step Solution:

Verification / Alternative check:
Biochemical assays measuring oxygen consumption, proton gradients, and ATP synthesis trace these processes to mitochondria and chloroplasts. Inhibitors like oligomycin (ATP synthase) and DCMU (photosystem II) further confirm organelle-specific energy generation.

Why Other Options Are Wrong:

• Chloroplasts and Golgi: Golgi does not perform oxidative or photo-phosphorylation.
• Mitochondria and ribosomes: ribosomes are translational machines, not energy generators.
• Mitochondria only: ignores ATP production in chloroplasts of photosynthetic organisms.
• ER and lysosomes: neither runs an energy-transducing electron transport chain.

Common Pitfalls:
Overlooking that plants use mitochondria as well; chloroplast ATP is not universally sufficient and mitochondria remain active, especially in the dark or in non-photosynthetic tissues.

Final Answer:
Mitochondria and chloroplasts