Questions
3–5 questions per paper
Difficulty
Medium
Importance
Conceptual core — essential for board success
Overview
Respiration in plants is the biochemical process of breaking down organic compounds to release energy in the form of ATP. It is a critical unit in the Class 11 curriculum, focusing on how cellular machinery converts glucose into usable chemical energy through aerobic and anaerobic pathways. Understanding the interconnectedness of metabolic cycles is essential for scoring well on metabolic-related questions.
Glycolysis (EMP Pathway)
Glycolysis is the initial phase of respiration occurring in the cytoplasm, where glucose is partially oxidized into two molecules of pyruvate. This pathway does not require oxygen and serves as the bridge between metabolic processes.
- Occurs in the cytosol of the cell
- Net gain of 2 ATP and 2 NADH per glucose molecule
- Key enzymes: Hexokinase, Phosphofructokinase, Pyruvate Kinase
- Conversion of 1 Glucose (6C) to 2 Pyruvate (3C)
- Also known as the EMP pathway (Embden-Meyerhof-Parnas)
Krebs Cycle (TCA Cycle)
Taking place in the mitochondrial matrix, the Krebs cycle completes the oxidation of pyruvate by stripping high-energy electrons from acetyl-CoA. It is the central hub for aerobic respiration and generates key electron carriers for the final stage.
- Pyruvate is converted to Acetyl-CoA before entry
- One cycle produces 3 NADH, 1 FADH2, and 1 GTP (ATP)
- Occurs in the mitochondrial matrix
- Condensation of Acetyl-CoA with oxaloacetic acid to form Citric Acid
- Carbon dioxide is released as a byproduct during decarboxylation steps
Electron Transport System (ETS)
The ETS represents the final stage of aerobic respiration where the energy trapped in NADH and FADH2 is utilized to generate a proton gradient. This gradient drives ATP synthase to produce the majority of ATP in the cell.
- Located in the inner mitochondrial membrane (cristae)
- Complexes I through IV facilitate electron flow
- Oxygen acts as the final electron acceptor
- Chemiosmosis explains the mechanism of ATP synthesis via proton gradient
- Produces significantly more ATP than glycolysis or the Krebs cycle
Formula Sheet
Glucose + 2 NAD+ + 2 ADP + 2 Pi -> 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP
2 Acetyl-CoA + 6 NAD+ + 2 FAD + 2 GDP + 2 Pi + 4 H2O -> 4 CO2 + 6 NADH + 2 FADH2 + 2 GTP + 6 H+ + 2 CoA
Exam Tip
Memorize the stoichiometry of ATP production: track the exact yield of NADH and FADH2 for every turn of the cycle to avoid calculation errors in board exams.
Common Mistakes
- Confusing the location of glycolysis (cytosol) with the Krebs cycle (mitochondrial matrix)
- Failing to account for the conversion of Pyruvate to Acetyl-CoA as a distinct step before the Krebs cycle
- Assuming oxygen is directly involved in the Krebs cycle (it is indirectly required only to regenerate NAD+ via the ETS)
More Revision Notes
Ready to test yourself?
Play topic-wise Respiration in Plants questions in Aspirant Arcade — gamified MCQ practice.
Download Free