NCERT Class 11-Biology: Chapter – 14 Respiration in Plants Part 7 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Long Answer Type Questions

Question 1:

In the following flow chart, replace the symbols a, b, c and d with appropriate terms. Briefly explain the process and give any two application of it.

Replace the Symbols



a = Glyceraldehyde – 3 – phosphate

b = PEP (Phosphoenol pyruvic acid)

The process is known as fermentation. After the glycolysis process, which doesn՚t require oxygen. We obtain pyruvic acid. Now if the cells have oxygen present, i.e.. , aerobic conditions are present in the cell, then this pyruvic acid goes on to the citric acid cycle or Tricarboxylic cycle in the mitochondria. But when there are anaerobic conditions the pyruvic acid gets converted to either lactic acid and it is known as homolactic fermentation. For examples, when our muscles do not receive oxygen, then homolactic fermentation occurs.

Also in some micro-organisms which are naturally anaerobic like yeast. They form C2H5OH and release CO2. This is known as alcoholic fermentation.

Two Applications of fermentation:

(i) Fermentation is widely used for the production of alcoholic beverage products like Whisky, Beer, etc.

(ii) Fermentation is widely used for the production of acids like citrus acid, lactic acid, alpha- amylase, etc.

Question 2:

Given below is a diagram showing ATP synthesis during aerobic respiration, replace the symbols A, B, C, D and E by appropriate terms given in the box.

ATP Synthesis

, Particle, Inner mitochondrial membrane, ATP, particle, ADP


It is the end product which is formed in ATP synthesis.

particle: The particle is a peripheral membrane protein complex and it has the site for the synthesis of ATP from ADP and inorganic phosphate.

: It is the inorganic phosphatase which is present along with ADP for the formation of ATP.

: For every ATP which is produced during the ATP synthesis process, the passes through from the inner mitochondrial space to the matrix down the electrochemical proton gradient.

Inner mitochondrial membrane It is the membrane from which ions pass through to the matrix.

Question 3:

Oxygen is critical for aerobic respiration. Explain its role with respect to ETS.


The role of oxygen is critical with respect to Electron Transport System (ETS) because:

(i) Oxygen plays a crucial role at the end of ETC because it removes the hydrogen from the electron transport system.

(ii) Oxygen acts as the final hydrogen acceptor in the electron transport chain.

(iii) If oxygen is not present, then the electrons could not pass through the co-enzymes.

(iv) Oxygen is responsible for the formation of the proton pump in the ETS process as it gives energy by the oxidation-reduction process.

(v) If oxygen is absent, then there will be no formation of proton pump and ATP will not be produced by oxidative phosphorylation.