Quick answer: A respiration in plants NEET PYQ analysis shows that NTA asks about two questions a year from this chapter, and they come from five areas: glycolysis (steps, ATP and NADH yield), the Krebs cycle (decarboxylation steps, substrate-level phosphorylation, location), the electron transport system with its five complexes, fermentation and the link reaction, and the respiratory quotient (RQ) with the amphibolic pathway. The 2024 to 2026 papers asked RQ, ETS, glycolysis and Krebs cycle questions.
This guide breaks down what NTA repeats, the tables to memorise and PYQ-pattern questions with answers. For the full plant physiology plan, see our plant physiology guide for NEET.
Want to test yourself first? Solve the Respiration in Plants PYQs for free, then use this guide to fix the gaps.
Table of Contents
Why Respiration in Plants Is High-Return
The chapter is a sequence of pathways, and its questions test where each step happens, what it makes and which enzyme does it. Once you can draw the pathways from memory, most questions become simple recall. For chapter notes, use our Respiration in Plants notes, and to see where it sits among other chapters, check the NEET 2027 chapter weightage.
Enzyme ideas such as cofactors and inhibition come from our Biomolecules PYQ analysis, and mitochondrial structure is in our Cell PYQ analysis.
Respiration in Plants NEET PYQ Analysis: What NTA Repeats
When you sort the past NEET biology PYQs from this chapter, five question types cover nearly everything.
| Question type | Frequency | What it tests |
|---|---|---|
| Krebs cycle | Most frequent | Steps, decarboxylations, substrate-level phosphorylation, products per turn |
| Glycolysis | Very frequent | Location, ATP-using and ATP-making steps, net yield |
| Electron transport system | Very frequent | Complexes I–V, cytochrome c, oxygen as the final acceptor, ATP synthase |
| Respiratory quotient | Regular | RQ of carbohydrates, fats and proteins |
| Fermentation, link reaction and amphibolic pathway | Regular | Alcoholic vs lactic acid fermentation, pyruvate dehydrogenase, why respiration is amphibolic |
For a quick warm-up, try these five quick plant physiology questions.
Where Each Step Happens
| Process | Location |
|---|---|
| Glycolysis | Cytoplasm |
| Fermentation | Cytoplasm |
| Link reaction (pyruvate → acetyl CoA) | Mitochondrial matrix |
| Krebs cycle | Mitochondrial matrix |
| Electron transport system and oxidative phosphorylation | Inner mitochondrial membrane |
Location questions appeared in both 2024 and 2026, so learn this table first.
Glycolysis (EMP Pathway)
Glycolysis was worked out by Embden, Meyerhof and Parnas, so it is also called the EMP pathway. It splits one glucose into two pyruvic acid molecules in the cytoplasm of all living organisms.
- Sucrose is first split into glucose and fructose by invertase.
- Glucose is phosphorylated by hexokinase.
- ATP used: two, at glucose → glucose-6-phosphate and fructose-6-phosphate → fructose-1,6-bisphosphate.
- NADH made: when PGAL (3-phosphoglyceraldehyde) is converted to 1,3-bisphosphoglycerate (BPGA).
- ATP made directly: at BPGA → 3-PGA and at PEP → pyruvic acid.
- Net yield per glucose: 2 ATP (4 made − 2 used) and 2 NADH, plus 2 pyruvate.
Fermentation
| Feature | Alcoholic fermentation | Lactic acid fermentation |
|---|---|---|
| Organisms | Yeast | Some bacteria; animal muscle during exercise |
| Products | Ethanol and CO₂ | Lactic acid |
| Enzymes | Pyruvic acid decarboxylase, alcohol dehydrogenase | Lactate dehydrogenase |
Fermentation releases less than 7% of the energy in glucose. Yeasts poison themselves when the alcohol concentration reaches about 13%.
The Link Reaction
Pyruvic acid enters the mitochondrial matrix and undergoes oxidative decarboxylation, catalysed by the pyruvate dehydrogenase complex with the coenzymes NAD⁺ and coenzyme A, and Mg²⁺:
Pyruvic acid + CoA + NAD⁺ → Acetyl CoA + CO₂ + NADH + H⁺
The Krebs Cycle (TCA Cycle)
The Krebs cycle, named after Hans Krebs, runs in the mitochondrial matrix.
- Acetyl CoA (2C) joins oxaloacetic acid (4C) and water to form citric acid (6C), catalysed by citrate synthase.
- Citrate is isomerised to isocitrate.
- Two successive decarboxylations follow, forming α-ketoglutaric acid (5C) and then succinyl CoA (4C).
- Succinyl CoA → succinic acid makes one GTP. This is the substrate-level phosphorylation step; the GTP is converted to ATP.
- Succinic acid → fumaric acid → malic acid → oxaloacetic acid, regenerating the 4C acceptor.
| Per acetyl CoA (one turn) | Yield |
|---|---|
| NADH | 3 |
| FADH₂ | 1 (at succinate → fumarate) |
| GTP/ATP | 1 |
| CO₂ | 2 |
Per glucose, the cycle turns twice, because one glucose gives two acetyl CoA.
The Electron Transport System
The ETS lies in the inner mitochondrial membrane.
| Component | Role |
|---|---|
| Complex I (NADH dehydrogenase) | Takes electrons from NADH and passes them to ubiquinone |
| Complex II | Takes electrons from FADH₂ (succinate dehydrogenase) to ubiquinone |
| Complex III (cytochrome bc₁) | Receives electrons from ubiquinol |
| Cytochrome c | Small mobile protein on the outer surface of the inner membrane; carries electrons from complex III to IV |
| Complex IV (cytochrome c oxidase) | Contains cytochromes a and a₃ and two copper centres; passes electrons to oxygen |
| Complex V (ATP synthase) | F₀ is the membrane channel for protons; F₁ is the head that makes ATP |
- Oxygen is the final hydrogen and electron acceptor, forming water. Without it, the whole chain stops.
- One NADH gives 3 ATP and one FADH₂ gives 2 ATP.
- The theoretical net gain from complete aerobic respiration of one glucose is 38 ATP. NCERT notes that this assumes an ideal, sequential pathway, so the real figure can be lower.
Respiratory Quotient (RQ)
RQ = volume of CO₂ evolved ÷ volume of O₂ consumed
| Respiratory substrate | RQ |
|---|---|
| Carbohydrates | 1 |
| Fats (e.g. tripalmitin: 102 CO₂ ÷ 145 O₂) | Less than 1 (about 0.7) |
| Proteins | About 0.9 |
The respiratory quotient of a fat was asked in 2026, and RQ calculations appear every few years.
The Amphibolic Pathway
Respiration is usually called catabolic, but NCERT calls it amphibolic, because it is involved in both breakdown and synthesis:
- Fats are broken into glycerol (which enters as PGAL) and fatty acids (which enter as acetyl CoA). When the plant needs fatty acids, acetyl CoA is withdrawn to make them.
- Proteins are broken into amino acids, which are deaminated and enter as pyruvic acid, acetyl CoA or Krebs cycle intermediates. The same intermediates are used to make amino acids.
Worked PYQ-Pattern Questions
Q1. The net gain of ATP directly from glycolysis of one glucose is: (a) 2 (b) 4 (c) 8 (d) 38
Answer: (a) 2. Four ATP are made, but two are used.
Q2. Where does the Krebs cycle take place?
Answer: In the mitochondrial matrix. The ETS is in the inner mitochondrial membrane, and glycolysis is in the cytoplasm.
Q3. The RQ of tripalmitin is about: (a) 1 (b) 0.9 (c) 0.7 (d) Infinity
Answer: (c) 0.7. It releases 102 CO₂ while using 145 O₂.
Q4. Substrate-level phosphorylation in the Krebs cycle occurs during the conversion of:
Answer: Succinyl CoA to succinic acid, which makes one GTP.
Q5. The final electron acceptor in the electron transport system is:
Answer: Oxygen, which is reduced to water.
Q6. Why is the respiratory pathway called amphibolic?
Answer: Because its intermediates are used both to break down substances (catabolism) and to build fatty acids and amino acids (anabolism).
Common Traps in This Chapter
- Placing glycolysis in the mitochondria
- Saying the Krebs cycle happens on the inner mitochondrial membrane
- Forgetting that glycolysis uses 2 ATP, so the net direct gain is 2, not 4
- Writing RQ of fats as more than 1
- Calling cytochrome c an integral protein of complex III
- Saying NADH gives 2 ATP and FADH₂ gives 3 (it is the other way round)
Practise Every Respiration in Plants PYQ
This respiration in plants NEET PYQ analysis shows you where the marks are. Solving real past questions makes the pathways automatic. Every Respiration in Plants previous year question is available chapter-wise, free:
👉 Solve all Respiration in Plants NEET PYQs
Keep the location table and the Krebs cycle steps beside you for the first round, then solve the second round without them.
Conclusion
Respiration in Plants is a chain of pathways, and NTA keeps asking where each step happens and what it makes. Use this respiration in plants NEET PYQ analysis to master glycolysis, the link reaction, the Krebs cycle, the ETS, fermentation, RQ and the amphibolic pathway. Then practise the past questions until each step comes without thinking.
FAQ
Q: How many questions come from Respiration in Plants in NEET? A: Usually about two questions a year, mostly on the Krebs cycle, glycolysis, the ETS and RQ.
Q: What is the most important topic in Respiration in Plants for NEET? A: The Krebs cycle is the most tested, especially its decarboxylation steps and substrate-level phosphorylation, followed by glycolysis and the ETS.
Q: What is the RQ of carbohydrates, fats and proteins? A: About 1 for carbohydrates, less than 1 (about 0.7) for fats, and about 0.9 for proteins.
Q: How many ATP are made from one glucose in aerobic respiration? A: A theoretical net gain of 38 ATP. NCERT notes this assumes an ideal pathway, so the actual figure can be lower.
Q: Why is respiration called an amphibolic pathway? A: Its intermediates are used both in breaking down food and in making fatty acids and amino acids.
Q: Where can I practise Respiration in Plants NEET PYQs for free? A: You can solve every Respiration in Plants previous year question chapter-wise for free using the practice links in this article.
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