Q.39 The citric-acid cycle takes place in
The citric acid cycle, also known as the Krebs or TCA cycle, occurs in the mitochondrial matrix in eukaryotic cells. This is the correct location for its eight enzymatic steps that oxidize acetyl-CoA to produce energy carriers like NADH and FADH2.
Option Analysis
(1) Mitochondrial Matrix
ThisThe citric acid cycle, also known as the Krebs or TCA cycle, occurs in the mitochondrial matrix in eukaryotic cells. This is the correct site for its aerobic oxidation of acetyl-CoA, producing energy carriers like NADH and FADH2.
Option Analysis
(1) Mitochondrial Matrix
This is the precise location where the eight enzymatic steps of the citric acid cycle unfold, fueled by acetyl-CoA from pyruvate oxidation.
The enzymes (except succinate dehydrogenase) reside here, linking to the electron transport chain on the inner membrane.
Essential for ATP production in respiration.
(2) Protoplast
Protoplast refers to plant cells without cell walls, but it lacks specificity for metabolic sites like the cycle.
No enzymatic activity of the cycle occurs here; it’s not a standard organelle term.
Irrelevant to Krebs cycle localization.
(3) Chloroplast Membrane
Chloroplasts handle photosynthesis, producing sugars, but the citric acid cycle is absent from their membranes or stroma.
Plants run the cycle in mitochondria, not chloroplasts, for respiration.
Confuses light-dependent reactions with dark respiration.
(4) Cell Membrane (Plasma Membrane)
The plasma membrane handles transport, not central metabolism like the cycle.
In prokaryotes, the cycle is cytosolic, but gradients form at the plasma membrane—still not the eukaryotic site.
Incorrect for standard biology contexts.
Correct Answer
(1) Mitochondrial Matrix
The citric acid cycle takes place in the mitochondrial matrix, a core fact for NEET, GATE Life Sciences, and CUET PG Botany exams. This SEO-optimized guide breaks down the question’s options—mitochondrial matrix, protoplast, chloroplast membrane, cell membrane—to clarify Krebs cycle location in plant and animal cells.
Citric Acid Cycle Basics
The citric acid cycle (TCA/Krebs) oxidizes acetyl-CoA in eukaryotes’ mitochondrial matrix, yielding 2 CO2, 3 NADH, 1 FADH2, and 1 GTP/ATP per turn.
It follows glycolysis and pyruvate decarboxylation, feeding electrons to oxidative phosphorylation.
Vital for your plant physiology and biochemistry prep.
Location Breakdown Table
| Option | Site Description | Correct for Citric Acid Cycle? | Reason |
|---|---|---|---|
| (1) Mitochondrial Matrix | Inner compartment of mitochondria | Yes | Hosts 7/8 enzymes; aerobic respiration hub |
| (2) Protoplast | Plant cell sans wall | No | Not an organelle; no cycle activity |
| (3) Chloroplast Membrane | Photosynthetic organelle membrane | No | Photosynthesis site, not respiration |
| (4) Cell Membrane | Plasma membrane | No | Transport role; prokaryote gradient only |
Exam Tips for Life Sciences
Master this: Glycolysis (cytosol), link reaction and TCA (matrix), ETS (cristae).
Common trap: Confusing with prokaryotes (cytosol) or plants’ chloroplast roles.
