Cell biology — Which cellular organelle is directly associated with photosynthesis (housing light reactions and carbon fixation in plants and algae)?
-
AGolgi complex
-
BMitochondrion
-
CLysosome
-
DChloroplast
-
EPeroxisome
Answer
Correct Answer: Chloroplast
Explanation
Introduction / Context:Photosynthesis is compartmentalized within chloroplasts in plants and algae. Recognizing organelle-function mapping is fundamental to cell biology and biochemistry, and it helps integrate topics like bioenergetics, plant physiology, and ecology.
Given Data / Assumptions:
- Thylakoid membranes in chloroplasts contain Photosystem I and II, cytochrome b6f, and ATP synthase.
- The Calvin–Benson cycle enzymes reside in the stroma of the chloroplast.
- Mitochondria perform aerobic respiration; Golgi handles protein modification and trafficking; lysosomes handle degradation.
Concept / Approach:Match function to organelle: photosynthetic light harvesting and electron transport occur in thylakoids, while carbon fixation occurs in the stroma—both compartments lie within chloroplasts.
Step-by-Step Solution:
Identify photosynthetic tasks → light reactions + carbon fixation.Locate these processes → thylakoids and stroma of chloroplasts.Select chloroplast as the correct organelle.Verification / Alternative check:Microscopy and biochemical fractionation consistently localize chlorophyll, RuBisCO, and ATP synthase to chloroplast compartments.
Why Other Options Are Wrong:
Golgi: glycosylation and sorting, not photosynthesis.Mitochondrion: oxidative phosphorylation with O2 as terminal electron acceptor.Lysosome: hydrolytic degradation, acidic lumen.Peroxisome: photorespiration peroxisomal steps in plants, but not primary photosynthetic reactions.Common Pitfalls:Confusing peroxisomal roles in photorespiration with photosynthesis; only chloroplasts perform the latter.
Final Answer:Chloroplast.