Mitochondria are the "powerhouses" of the cell, breaking down fuel molecules and capturing energy in cellular respiration.

Introduction to Cellular Respiration
Cellular respiration is a crucial biological process that enables cells to convert biochemical energy from nutrients into adenosine triphosphate (ATP), which powers various cellular activities. The organelle primarily responsible for this process is the mitochondria.
Mitochondria: The Powerhouse of the Cell
- Structure: Mitochondria are double-membraned organelles found in most eukaryotic cells. They contain their own DNA and ribosomes, supporting their role in energy production.
- Function: Mitochondria are involved in aerobic respiration, which includes several key stages:
- Glycolysis: Takes place in the cytoplasm, breaking glucose down into pyruvate.
- Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix, where pyruvate is further broken down, releasing electron carriers (NADH and FADH2).
- Electron Transport Chain (ETC): Located in the inner mitochondrial membrane, where electrons from NADH and FADH2 are transferred through a series of proteins, ultimately producing ATP through oxidative phosphorylation.
Comparison with Other Organelles
- Endoplasmic Reticulum: Primarily involved in protein and lipid synthesis, not respiration.
- Chloroplast: Found in plant cells, responsible for photosynthesis, converting light energy into chemical energy, but not directly involved in respiration.
- Golgi Complex: Functions in modifying, sorting, and packaging proteins and lipids for secretion or delivery, unrelated to respiration.
Conclusion
Given its vital role in energy production and metabolism, the mitochondria are rightly referred to as the "powerhouse of the cell," making option 'A' the correct answer for the organelle involved in respiration.