CBSE Questions for Class 11 Medical Biology Respiration In Plants Quiz 5 - MCQExams.com

• Glycolysis is the breakdown of complex carbohydrates into the simpler form, i.e., pyruvic acid. Thus, X represents glycolysis. 
• In the absence of oxygen pyruvic acid further converts into alcohol and carbon dioxide with a lesser amount of energy i.e., fermentation or anaerobic respiration or anoxybiotic. Thus, Z represents anoxybiotic. 
• In the presence of oxygen (aerobic respiration), pyruvic acid will be converted into carbon dioxide, water, and a large amount of energy. Aerobic respiration is also known as oxybiotic respiration. Thus, Y represents oxybiotic. 

• Glycolysis is the process of partial oxidation of glucose into two molecules of pyruvic acid through ten enzyme-mediated reactions releasing ATP and reducing NADH$$_2$$. 
• It is common in both aerobic and anaerobic respiration. It occurs in the cytoplasm. 
• It has two phases, preparatory and pay off. 
• In the preparatory phase, glucose is broken down to glyceraldehyde-3-phosphate. 
• In the pay off phase, it is changed into pyruvate and produces NADH and ATP.

• The citric acid cycle is also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle. 
• It is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins, into adenosine triphosphate (ATP) and carbon dioxide.
•  In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion.
•  In prokaryotic cells, such as bacteria, which lack mitochondria, the citric acid cycle reaction sequence is performed in the cytosol. 
• Hence, Mitochondria is the site for the Krebs cycle.
• So, the correct answer is 'Krebs cycle'.

$$\textbf{Correct Option B & C}$$

$$\textbf{Solution}$$

$$\bullet$$ Breathing and respiration are two different process.

Correct Option: B

Explanation for the correct option:

•  Glycolysis converts glucose into two 3-carbon molecules called pyruvate. 
• The energy released during glycolysis is used to make ATP. 
• Enolase is used to convert 2-phosphoglycerate (2PG) to phosphoenolpyruvate (PEP) in the 9th reaction of glycolysis. 
• It is a reversible dehydration reaction. 

• During light reactions, 4e- will be released.

• During dark reactions, 8e- will be released.
• All together 12 electrons are involved for the formation of 1 mole of glucose and 6 O$$_{2}$$ molecules.

Solution:

Correct answer is option B.

Explanation for correct option:

• Kreb cycle is the second phase of aerobic respiration and starts with the condensation of acetyl CoA with OAA forms citrate, the first tricarboxylic acid of Kreb cycle. That's why it is also called as citric acid cycle and tricarboxylic acid cycle.
• Calvin cycle refers to the enzymatic reaction that fixes carbon dioxide into carbohydrates. Series of reactions that produce urea from ammonia are collectively termed the urea cycle. 

Kreb cycle produces 8 molecules of NADH plus 2 molecules of $$FADH_2$$ (via succinate dehydrogenase) in the mitochondrial matrix. During electron transport through the inner mitochondrial membrane, NADH and $$FADH_2$$ pump electrons through a series of electron transport proteins to final acceptor oxygen. This electron transport chain ensures availability of NAD and FAD for next round of Kreb cycle. Nonavailability of these reducing powers results in entry of pyruvate in anaerobic respiration pathway. So, to maintain continuity of Kreb cycle, oxidation of NADH and $$FADH_2$$ by oxygen is prerequisite and the cycle is considered aerobic. Thus, the correct answer is option D.