1. Gas Exchange in Plants vs Animals
| Feature | Plants | Animals |
|---|---|---|
| Specialised respiratory organs | Absent | Present in most animals |
| Gas-exchange structures | Stomata and lenticels; diffusion through surfaces and air spaces | Specialised organs and transport systems support gas exchange |
| Gas transport within body | Very little transport from one plant part to another; each part meets its own needs | Often involves dedicated transport to tissues |
| Demand for exchange | Relatively low in roots, stems and leaves | Generally higher metabolic demand |
| Structural basis | Living cells lie close to surface; loose parenchyma creates connected air spaces | Respiratory surfaces and circulation bring gases to cells |
2. Glycolysis vs Krebs Cycle
| Feature | Glycolysis | Krebs / TCA cycle |
|---|---|---|
| Site | Cytoplasm; occurs in all living organisms | Mitochondrial matrix in eukaryotes |
| Starting substrate | Glucose (6C) | Acetyl CoA (2C) condenses with oxaloacetate |
| Key outcome | Partial oxidation to two pyruvate (3C) molecules | Complete oxidation of acetyl group to CO2; oxaloacetate regenerated |
| ATP and reduced coenzymes | Net 2 ATP; 2 NADH + H+ formed per glucose | Per glucose: 2 ATP/GTP, 6 NADH + H+ and 2 FADH2 |
| Oxygen requirement | Does not directly require O2 | Continues only when NAD+ and FAD are regenerated through O2-dependent ETS |
EMP pathway Glycolysis is named after Embden, Meyerhof and Parnas. In anaerobic organisms it is the only respiratory process.
3. Fates of Pyruvate
| Pathway | Conditions / location | Products and enzymes |
|---|---|---|
| Alcoholic fermentation | Anaerobic; yeast and some microorganisms | CO2 + ethanol; pyruvate decarboxylase and alcohol dehydrogenase |
| Lactic acid fermentation | Anaerobic; some bacteria and oxygen-deficient exercising muscle | Lactic acid; lactate dehydrogenase |
| Aerobic respiration | Presence of O2; pyruvate enters mitochondrion in eukaryotes | Acetyl CoA, then CO2, H2O and large ATP yield |
| Shared redox point | Fermentation reoxidises NADH + H+ to NAD+, allowing glycolysis to continue. | |
4. Fermentation vs Aerobic Respiration
| Feature | Fermentation | Aerobic respiration |
|---|---|---|
| Oxygen | Anaerobic | Requires O2; O2 is terminal hydrogen/electron acceptor |
| Extent of glucose breakdown | Partial | Complete to CO2 and H2O |
| End products | Ethanol + CO2 or lactic acid | CO2 + H2O |
| Net ATP per glucose | 2 ATP; less than 7% of glucose energy released | Theoretical net gain of 38 ATP under stated assumptions |
| NADH oxidation | Relatively slow; NADH reduces pyruvate/derivative | Vigorous oxidation through ETS and oxidative phosphorylation |
| Hazard | Accumulation of acid or alcohol can be harmful; yeast dies near 13% alcohol | Does not accumulate these fermentation products |
5. Matrix Events vs Inner-Membrane Events
| Feature | Mitochondrial matrix | Inner mitochondrial membrane |
|---|---|---|
| Pyruvate oxidation | Pyruvate dehydrogenase converts pyruvate to acetyl CoA + CO2 + NADH | Not the site of oxidative decarboxylation |
| TCA cycle | Acetyl CoA oxidation, CO2 release, NADH and FADH2 formation | Not the site of the cycle |
| ETS | Provides NADH and FADH2 to the membrane system | Complexes I-IV transfer electrons to O2 |
| ATP production | Substrate-level phosphorylation yields GTP/ATP at succinyl CoA conversion | ATP synthase / complex V carries out oxidative phosphorylation |
6. NADH vs FADH2 in Electron Transport System
| Feature | NADH + H+ | FADH2 |
|---|---|---|
| Entry point | NADH dehydrogenase, complex I | Complex II during succinate oxidation |
| Electron path | Complex I -> ubiquinone -> complex III -> cytochrome c -> complex IV -> O2 | Ubiquinone -> complex III -> cytochrome c -> complex IV -> O2 |
| ATP yield in NCERT balance sheet | 3 ATP per NADH | 2 ATP per FADH2 |
| Final acceptor | Oxygen accepts electrons/hydrogen at terminal stage and is reduced to water. | |
ATP synthase F0 forms the proton channel; F1 contains ATP-synthesis site. About 4H+ pass through F0 per ATP produced.
7. Carbohydrates vs Fats vs Proteins as Respiratory Substrates
| Substrate | Entry into respiratory pathway | Key processing step |
|---|---|---|
| Carbohydrates | Usually converted to glucose, then enter glycolysis | Glucose is the favoured respiratory substrate |
| Fats | Glycerol enters after conversion to PGAL; fatty acids enter as acetyl CoA | Fat splits into glycerol and fatty acids before respiration |
| Proteins | Amino acids can enter as pyruvate, acetyl CoA or TCA-cycle intermediates | Proteases digest proteins; amino acids undergo deamination |
| Pathway character | Respiratory intermediates are both broken down and withdrawn for synthesis, so respiration is amphibolic - both catabolic and anabolic. | |
8. Respiratory Quotient of Major Substrates
| Respiratory substrate | Respiratory quotient (RQ) | Reason / NCERT value |
|---|---|---|
| Carbohydrates | 1.0 | Equal volumes of CO2 released and O2 consumed during complete oxidation |
| Fats | Less than 1 | Tripalmitin gives RQ = 102/145 = 0.72 |
| Proteins | About 0.9 | Protein respiration usually does not occur in isolation in living organisms |
| Formula | RQ = volume of CO2 evolved / volume of O2 consumed | |
Balance-sheet caution The theoretical 38 ATP yield assumes an orderly sequential pathway, mitochondrial transfer of glycolytic NADH, no diversion of intermediates, and glucose as the only substrate - conditions not fully met in living cells.