NEET Biology • Class XI • Chapter 12
Respiration in Plants
NTA NEET (UG) syllabus
Respiration in plants NEET questions test how cells break down glucose to make ATP: glycolysis, fermentation, the TCA cycle, the electron transport system, the balance sheet and the respiratory quotient. This hub follows the NCERT Class XI Biology chapter and splits it into 8 short topics in NCERT order. Pick a card to study one topic at a time.
- 8 topics
- Glycolysis • Krebs cycle • ETS
- Net ATP & RQ
Topics in this chapter
Each card opens its own article. Cards marked “Coming soon” are being written.
Do Plants Breathe?
Section 12.1
How plants exchange gases without lungs, and what cellular respiration really means.
- Respiration vs breathing
- Respiratory substrates & ATP as energy currency
- Gas exchange through stomata & lenticels
- Why plants need no specialised respiratory organs
- Overall equation of aerobic respiration
- Aerobic vs anaerobic respiration
Glycolysis
Section 12.2
The EMP pathway: glucose to two pyruvic acid in the cytoplasm, step by step.
- EMP pathway & where it occurs
- Sucrose → glucose + fructose (invertase)
- Hexokinase & the 10 steps
- 2 ATP used, 4 ATP made (net 2)
- NADH + H⁺ formation (PGAL → BPGA)
- Fates of pyruvic acid
Fermentation
Section 12.3
How pyruvic acid is handled without oxygen: alcoholic and lactic acid fermentation.
- Alcoholic fermentation in yeast
- Pyruvic acid decarboxylase & alcohol dehydrogenase
- Lactic acid fermentation in bacteria & muscles
- Lactate dehydrogenase & NADH + H⁺
- Energy released (<7%) & the 13% alcohol limit
Aerobic Respiration & the Tricarboxylic Acid Cycle
Sections 12.4, 12.4.1
Pyruvate oxidation in the mitochondrial matrix and the TCA (citric acid / Krebs) cycle.
- Oxidative decarboxylation: pyruvate → acetyl CoA
- Pyruvic dehydrogenase, Mg²⁺ & NAD⁺
- Citrate formation: acetyl CoA + OAA
- Steps of the TCA cycle
- NADH, FADH₂, GTP/ATP & CO₂ from one cycle
Electron Transport System & Oxidative Phosphorylation
Section 12.4.2
How NADH and FADH₂ are oxidised on the inner mitochondrial membrane to make ATP.
- Complexes I–V of the ETS
- Ubiquinone & cytochrome c as mobile carriers
- Oxygen as the final hydrogen acceptor
- ATP synthase: F₀ & F₁
- Chemiosmosis & proton gradient
The Respiratory Balance Sheet
Section 12.5
Counting the net ATP from one glucose, and the assumptions behind the number.
- Assumptions of the balance sheet
- Net gain of 38 ATP in aerobic respiration
- Why the real yield differs
- Fermentation vs aerobic respiration compared
Amphibolic Pathway
Section 12.6
Why respiration is both catabolic and anabolic: fats and proteins enter and leave it.
- Entry of fats: glycerol & fatty acids
- Entry of proteins: amino acids
- Intermediates withdrawn for synthesis
- Why respiration is called amphibolic
Respiratory Quotient
Section 12.7
The ratio of CO₂ released to O₂ consumed, and its value for each substrate.
- Definition: RQ = CO₂ evolved / O₂ consumed
- RQ of carbohydrates (1)
- RQ of fats (<1, e.g. tripalmitin 0.7)
- RQ of proteins (about 0.9)
- RQ in anaerobic respiration
Key ideas to remember
Where it happens: glycolysis and fermentation take place in the cytoplasm; the TCA cycle in the mitochondrial matrix; the ETS and oxidative phosphorylation on the inner mitochondrial membrane.
Numbers NEET loves: net 2 ATP from glycolysis, net 38 ATP per glucose in aerobic respiration (theoretical), RQ = 1 for carbohydrates, about 0.7 for fats and 0.9 for proteins.
Respiration in Plants NEET: Common doubts
Do plants respire at night only?
No. Plants respire all the time, day and night, in every living cell. During the day, photosynthesis is usually faster than respiration, so the CO₂ released by respiration is hidden by the O₂ given out.
What is the difference between breathing and respiration?
Breathing is the exchange of gases between an organism and its surroundings. Respiration is the breakdown of food (such as glucose) inside cells to release energy that is trapped as ATP.
Why is glycolysis common to aerobic and anaerobic respiration?
Glycolysis does not need oxygen and takes place in the cytoplasm, so every organism can carry it out. What happens to pyruvic acid afterwards depends on whether oxygen is present.
Why is the Krebs cycle called the tricarboxylic acid cycle?
Its first product, citric acid, has three carboxyl (–COOH) groups. That is why it is also called the citric acid cycle.
Why is oxygen called the final hydrogen acceptor?
At the end of the electron transport system, oxygen accepts electrons and protons to form water. Without oxygen, the chain stops and NADH cannot be reoxidised.
What is the RQ of fats, and why is it less than one?
Fats are poor in oxygen, so they need more O₂ for oxidation than the CO₂ they release. For example, tripalmitin has an RQ of about 0.7.