Respiration in Plants: Visual Summary

Citric Acid (Krebs) Cycle — central stage of aerobic cellular respiration Image: Overview of cellular respiration stages — Wikimedia Commons (public domain)

Conceptual Flow

Comparative Summary Table

Feature	Glycolysis	Link Reaction	TCA Cycle	ETS
Location	Cytoplasm	Mito. matrix	Mito. matrix	Inner mito. membrane
$O_{2}$ needed?	No	No	No (indirect)	Yes (final acceptor)
ATP produced (direct)	2 ATP	0	2 GTP	34 ATP
NADH produced	2	2	6	0 (consumed)
$FADH_{2}$ produced	0	0	2	0 (consumed)
$CO_{2}$ released	0	2	4	0

RQ Visual Reference

Substrate	RQ Value	Visual Cue
Carbohydrates (glucose)	1.0	Equal gases; perfectly balanced
Fats (tripalmitin)	~0.7	"Low" — fat needs more $O_{2}$
Proteins	~0.8	Middle value
Organic acids (malic)	~1.33	"High" — already oxidised
CAM plants (night)	∞	Off the chart — no external $CO_{2}$

Key Structural Landmark: Mitochondrion

The mitochondrion is the powerhouse of aerobic respiration. Its double-membrane structure is functionally critical:

Outer membrane: Permeable to small molecules; not involved in ATP synthesis
Intermembrane space: Accumulates $H^{+}$ during ETS — high [ $H^{+}$ ], low pH
Inner membrane (cristae): Site of ETS complexes (I–IV) and ATP synthase; highly folded to maximise surface area
Matrix: Site of TCA cycle and link reaction; contains TCA enzymes and mtDNA