NCERT Class 11-Biology: Chapter – 14 Respiration in Plants Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 18:

RuBP carboxylase, PEP case, Pyruvate dehydrogenase, ATPase, cytochrome oxidase, Hexokinase, Lactate dehydrogenase. Select/choose enzymes from the list above which are involved in

a. Photosynthesis

b. Respiration

c. Both in photosynthesis and respiration


a. Enzymes used in photosynthesis are:

  • RuBP
  • PEP carboxylase
  • ATPase
  • b. Enzymes used in respiration are:
  • Hexokinase
  • ATPase
  • Pyruvate dehydrogenase
  • Cytochrome oxidase
  • c. Enzyme used in both in photosynthesis and respiration are:
  • ATPase

Question 19:

How does a tree trunk exchange gases with the environment although it lacks stomata?


A tree trunk exchanges gases with the environment although it lacks the stomata because it has lenticels through which oxygen and other gas exchange occurs. They are cells consisting of large intercellular pores.

Question 20:

Write two energy yielding reactions of glycolysis.


Two energy yielding reactions of glycolysis:

  • Conversion of 1,3 – bisphosphoglyceric acid (1,3 – BPGA) to 3 – Phosphoglyceric acid (3 – PGA) .
  • Conversion of 3- phosphoenolpyruvate (3 - PEP) to pyruvic acid.

Question 21:

Name the site (s) of pyruvate synthesis. Also, write the chemical reaction wherein pyruvic acid dehydrogenase acts as a catalyst.


The site of pyruvate synthesis is Cytoplasm in the cell.

Question 22:

Mention the important series of events of aerobic respiration that occur in the matrix of the mitochondrion as well as one that take place in inner membrane of the mitochondrion.


The important series of events of aerobic respiration that occur in the matrix of the mitochondrion and in the inner membrane of the mitochondrion are:

(i) Citric Acid Cycle/Tricarboxylic acid cycle: It occurs in the mitochondrial matrix of the cell.

(ii) Electron transport system/Oxidative phosphorylation: It occurs in the inner mitochondrial membrane of the cell.

Question 23:

Respiratory pathway is believed to be a catabolic pathway. However, nature of TCA cycle is amphibolic. Explain.


The respiratory pathway is considered to be a catabolic pathway because it involves only the breakdown of substrate for example in glycolysis the glucose is broken down to form pyruvate. But in the tricarboxylic cycle (TCA cycle) the pyruvate is further broken down to Acetyl CoA, and this Acetyl CoA can also be synthesized to fatty acid whenever it is required for fatty acid metabolism or synthesis. Thus, During the TCA cycle, it is observed that both breakdown and synthesis of substrates occur. Therefore, the TCA cycle exhibits Amphibolic nature as it shows both catabolism and anabolism.