Class 11 Biology - ISC
Respiration in Plants
The chapter 'Respiration in Plants' explores how plants break down complex organic compounds, primarily glucose, to release energy essential for cellular activities. For Class 11 ISC students, mastering this topic is crucial as it bridges photosynthesis and plant growth. You will study the step-by-step mechanisms of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport system. Understanding aerobic versus anaerobic pathways, the calculation of net ATP yield, and the respiratory quotient (RQ) is vital for scoring well in both board exams and competitive entrances like NEET.
Start Learning FreeKey Concepts
Glycolysis
The initial breakdown of one molecule of glucose into two molecules of pyruvic acid, occurring in the cytoplasm without requiring oxygen.
Krebs Cycle (TCA Cycle)
A series of enzyme-catalyzed chemical reactions in the mitochondrial matrix where acetyl-CoA is completely oxidized to carbon dioxide, releasing NADH, FADH2, and ATP.
Electron Transport System (ETS) and Oxidative Phosphorylation
The transfer of electrons along a series of coenzymes in the inner mitochondrial membrane, driving protons across to synthesize ATP via ATP synthase.
Fermentation (Anaerobic Respiration)
A partial breakdown of glucose in the absence of oxygen, resulting in ethanol or lactic acid and a very low net yield of ATP.
Respiratory Quotient (RQ)
The ratio of the volume of CO2 evolved to the volume of O2 consumed during respiration, which helps determine the type of respiratory substrate being used.
Important Formulas
Board Exam Info
In the ISC Class 11 Biology examination, this chapter typically carries around 5 to 7 marks. Questions frequently include direct pathways (like drawing or explaining glycolysis and the Krebs cycle), numerical problems based on the Respiratory Quotient (RQ), and distinguishing between aerobic respiration and fermentation.
Frequently Asked Questions
Why is the net gain of ATP 36 in some textbooks and 38 in others?
It depends on the shuttle system used to transport NADH from the cytoplasm into the mitochondria. The glycerol-phosphate shuttle yields 36 ATP, while the malate-aspartate shuttle yields 38 ATP.
What is the respiratory quotient for fats and organic acids?
For fats (tripalmitin), the RQ is less than 1 (approx. 0.7) because they consume more oxygen than they evolve carbon dioxide. For organic acids like malic acid, the RQ is greater than 1.
Is oxygen strictly required for the Krebs cycle?
While the Krebs cycle does not directly use oxygen, it stops functioning in the absence of oxygen because the preceding ETS requires oxygen as the final electron acceptor to regenerate NAD+ and FAD.
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