Study the given flow chart and answer any of the  four questions from (a) to (e). 

Question 3.jpg

(a) Identify X, Y and Z.  

(i) X-Glycolysis, Y-Anaerobic, Z-Aerobic  

(ii) X-Krebs cycle, Y-Aerobic, Z-Anaerobic  

(iii) X-Glycolysis, Y-Aerobic, Z-Anaerobic  

(iv) X-Glycolysis, Y-Aerobic, Z-Krebs's cycle  



Breakdown of Glucose inside cell-01.jpg

  • Carbohydrates are broken down into pyruvic acid by the process of glycolysis . ( Glycos means glucose and lysis means breakdown , so glycolysis is the breakdown of glucose.)
  • In the presence of oxygen , pyruvic acid is broken down aerobically into CO 2 and H 2 O to release a large amount of energy.
  • In the absence of oxygen , pyruvic acid is broken down anaerobically into CO 2 and C 2 H 5 OH to release a small amount of energy.


Thus, X is Glycolysis, Y is Aerobic, Z is Anaerobic

Labelled flow chart-01.jpg

So, the correct option is (iii) 


(b) The process X occurs in  ________  and Y occurs in  _________ part of the cell.  

(i) Mitochondria and cytoplasm respectively  

(ii) Cytoplasm and mitochondria respectively  

(iii) Both takes place in cytoplasm  

(iv) Both takes place in mitochondria  



  • Glycolysis occurs in the cytoplasm of the cell 
  • And, pyruvic acid is broken down aerobically into CO 2 , H 2 O and energy inside the mitochondria .
  • That is why mitochondria is known as the powerhouse of the cell .

Labelled flow chart-01.jpg

So, the correct answer is (ii) - Cytoplasm, mitochondria respectively.

(c) In which of these organisms the process Z takes  place?  

(i) (i) Bacteria 

(ii) (ii) Humans  

(iii) (iii) Yeast 

(iv) (iv) Spirogyra  



The process Z i.e. anaerobic breakdown of pyruvic acid to produce ethanol and CO 2 is also known as fermentation and it takes place in yeast.

This is the reason why yeast is used in alcohol producing and bread making industries 

Anaerobic Respiration reaction-01.jpg

So, the correct answer is (iii) Yeast 


(d) In which part of the human body does the process Z take place?  

(i) In muscle cells 

(ii) In kidneys  

(iii) In liver cells 

(iv) In leydig’s cell  



When we do heavy exercise, there is a scarcity of O 2 due to which the glucose in our muscles breaks down anaerobically.

Anaerobic Respiration reaction in muscles-01.jpg

So, the correct option is (i) In muscle cells  

(e) Where does aerobic respiration occur in a cell?   

(i) Mitochondria 

(ii) Cytoplasm  

(iii) Nucleus 

(iv) Plastid  



Mitochondria is responsible for breaking down glucose in the presence of air (aerobic respiration)

Thus, the correct answer is, (i) Aerobic respiration occurs in the mitochondria of  the cell.

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo