Biology

Cellular Respiration and Enzymes

1,551 Questions

Explore key concepts of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. These questions also cover ATP production, anaerobic respiration, and essential metabolic pathways. This topic forms a core part of the biology syllabus for many competitive examinations.

Glycolysis and metabolic pathwaysKrebs cycle processesElectron transport chainATP production countAnaerobic respiration products

Cellular Respiration and Enzymes Questions

Multiple choice biology life processes in living organisms- part 1 fermentation cell respiration living organisms and energy production

Choose the correct answers from the alternatives given :
Which of these is not true of fermentation?

  1. Net gain of only two ATP

  2. Occurs in cytosol

  3. NADH donates electrons to electron transport system

  4. Begins with glucose
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

  • Fermentation is the process that takes place after the glycolysis in the cells where the anaerobic respiraton occurs due to absence or lack of oxygen.
  • Pyruvic acid which is formed at the end of the glycolysis by the break down of the glucose molecule enters the fermentation reaction in the anaerobic cells.
  • During fermentation reaction the pyruvic acid is converted to lactic acid and one molelcule of NADH is formed per molecule of pyruvic acid.
  • This molecule of NADH will only form ATP when it will undergo oxidative phosphorylation in the electron transport chain which takes place in mitochondria, but for this process presence of oxygen is required so the organisms or the cells performing anaerobic respiration cannot perforem this process therefore the NADH formed will not donate electron to the ETS and no ATP will be formed by that.
  • Therefore the answer option 'NADH donates electrons to electron transport system' is correct.










Multiple choice biology respiration in plants fermentation cell respiration living organisms and energy production

State whether the following statements are true or false.
When not enough oxygen gets to muscle cells during a sprint, energy is provided by glycolysis of glucose to pyruvic acid and then conversion of these molecules to lactic acid.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • Glycolysis is the first part of both aerobic and anaerobic respiration.
  • The end product of glycolysis is pyruvic acid which is produced in the cytoplasm and no oxygen is required for the process of glycolysis.
  • The pyruvic acid formed can enter either kerb cycle for the reactions of aerobic respiration or it can undergo anaerobic reaction in the cells where there is absence of oxygen.
  • There are 2 process under anaerobic reaction in which pyruvic acid can take part. First is where pyruvic acid is converted to lactic acid and second is where it converted to Ethanol and carbon dioxide. These reaction are called fermentation reaction.
  • Fermentation reaction of pyruvic acid takes place when there is no presence of oxygen. Sometimes during some of the physical activities when not enough oxygen is not reaching the muscles the energy for the contraction and relaxation of the muscles is provided by the process of glycolysis (2ATP) and then the pyruvic acid undergoes fermentation reaction forming Lactic acid and releasing 1 molecule of NADH per Pyruvic acid molecule.
  • Therefore the above sentence is correct and the answer option 'True' is correct.
Multiple choice biology life processes in living organisms- part 1 fermentation cell respiration living organisms and energy production

Choose the correct answers from the alternatives given :
Which of these pairs of processes are anaerobic?

  1. Fermentation and glycolysis

  2. Fermentation and the Krebs cycle

  3. Glycolysis and the Krebs cycle

  4. The Krebs cycle and the electron transport system
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Respiration is of two types -

Aerobic respiration - It is the process of complete oxidation of organic foods into carbon dioxide and water in the presence of oxygen. it has three steps ;
  • Glycolysis - It occurs in the cytoplasm in which glucose breaks into two molecules of pyruvate. It occurs in both aerobic and anaerobic respiration.
  • Krebs cycle occurs in the mitochondria where oxidative decarboxylation of pyruvate takes place to form acetyl CoA.
  • Electron transport system - Here series of coenzymes and cytochromes acts as a passage of electron.
Anaerobic respiration - It is the process of incomplete oxidation of organic foods. oxygen is not utilized in this process, this occurs in the process of fermentation.
So, the correct option is ' Fermentation and glycolysis'.

Multiple choice biology respiration in plants fermentation cell respiration living organisms and energy production

Formation of lactic acid from pyruvate requires

  1. Decarboxylation

  2. Reduction

  3. Oxidation

  4. Hydration
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pyruvate + NADH $\rightarrow$ Lactic acid + NAD$^{+}$
Muscle cells convert pyruvate into lactate. Here, pyruvate (a metabolite of glucose) is reduced to lactic acid by accepting electrons from NADH, which oxidizes NADH back to NAD$^{+}$ to allow glycolysis to continue under anaerobic conditions. 

Multiple choice biology life processes in living organisms- part 1 fermentation cell respiration living organisms and energy production

Anaerobic respiration following glycolysis is

  1. Oxidative phosphorylation

  2. Krebs cycle

  3. Fermentation

  4. Both A and B
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Following glycolysis, if the oxygen is available, end products of glycolysis directly enter Krebs' cycle for further oxidation and energy production. In anaerobic conditions, it chooses to get fermented and the end product is another organic substance which is incompletely oxidised, producing less energy.

So, the correct answer is 'Fermentation'.

Multiple choice biology life processes in living organisms- part 1 fermentation cell respiration living organisms and energy production

Anaerobic respiration is

  1. Complete oxidation

  2. Incomplete oxidation

  3. Anabolic reaction

  4. Fermentation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The process of fermentation is the form of anaerobic respiration carried by some microorganisms. Many microorganisms such as fungus and bacteria can grow and flourish in the complete absence of oxygen. Such microorganisms can utilize sugars to convert it into ethanol and evolve carbon dioxide. Since it is the incomplete breakdown of glucose, it yields small amount of energy which is sufficient to maintain the life of organisms like yeast and bacteria. 

Thus, the correct answer is 'Fermentation'.

Multiple choice biology molecular biology fermentation cell respiration living organisms and energy production

Which of the following is the byproduct of anaerobic respiration in muscles?

  1. Sugar

  2. Lactic acid

  3. HCl

  4. Oxygen
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Anaerobic respiration is the breakdown of glucose in the absence of oxygen. In humans, oxygen-starved muscle cells will respire anaerobically under stress such as heavy physical activity. The by-product of anaerobic respiration in muscles is the lactic acid which causes the puffed out feeling. There is a build-up of lactic acid in the muscles during vigorous exercise. The lactic acid needs to be oxidised to carbon dioxide and water later.
So, the correct answer is 'Lactic acid'.

Multiple choice biology biological molecules energy giving food carbohydrate and its test food and it's constituents

How many NADH molecules are produced during the complete breakdown of one molecules of glucose?

  1. 5

  2. 10

  3. 30

  4. 6
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

During the complete breakdown of one glucose molecule via glycolysis, the link reaction, and the Krebs cycle, a total of 10 NADH molecules are produced (2 in glycolysis, 2 in the link reaction, and 6 in the Krebs cycle). In addition, 2 FADH2 molecules are also produced.

Multiple choice biology enzymes classification of enzyme enzymes classification and cofactors the origin of cells and cell division

Hexokinase (Glucose $+$ ATP $\longrightarrow$ Glucose 6-P $+$ ADP) belongs to the category

  1. Transferases

  2. Lysases

  3. Oxidoreductases

  4. Isomerases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Transferase is an enzyme which transfers a group from one molecule to another molecule. Hexokinase is the enzyme which transfers one phosphate from ATP to glucose and forms glucose 6-phosphate.

(Glucose ++ ATP ⟶⟶ Glucose 6-P ++ ADP)
Thus, the correct answer is A.

Multiple choice biology enzymes classification of enzyme enzymes classification and cofactors the origin of cells and cell division

Enzymes functional in cells are called

  1. Endoenzymes

  2. Exoenzymes

  3. Apoenzymes

  4. Isoenzymes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Endoenzyme is the cells which function inside the cell. It is also known as intracellular enzymes. It helps in the catalysis of the intracellular metabolic reaction. 

Exoenzymes are the enzymes which function outside the cell.
Isoenzyme is also known as isozyme. When the two enzymes differ in amino acid sequence but catalyze the same chemical reaction they are known as isoenzyme. They are two different molecular form of the enzyme.
Enzymes are proteins which help to catalyze the biochemical reaction. The enzyme has a protein part which is not active is known as apoenzyme.
So, the correct answer is option A.

Multiple choice biology enzymes classification of enzyme enzymes classification and cofactors the origin of cells and cell division

Which enzyme is concerned with transfer of electrons?

  1. Desmolase

  2. Hydrolase

  3. Dehydrogenase

  4. Transaminase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Desmolase catalyzes the formation or destruction of carbon-carbon bonds within a molecule. It is involved in the transfer of electrons.
Hydrolase is the enzyme which catalyzes the splitting of compounds by addition of water.
Dehydrogenase is an enzyme which participates in the oxidoreductase reaction by using an electron acceptor.
Transaminase catalyzes aminotransferase reaction between an amino acid and a α-keto acid.
So, the correct answer is option B.
Multiple choice biology enzymes classification of enzyme enzymes classification and cofactors the origin of cells and cell division

Match and find the correct option.

$(a)$ Oxidoreductases $(i)$ Linking of the compounds
$(b)$ Isomerases $(ii)$ Removal of group from substrate
$(c)$ Ligases $(iii)$ Interconversion of isomers
$(d)$ Lyases $(iv)$ Dehydrogenases
$(v)$ Hydrolysis
  1. $a - iv, b - i, c - iii, d - ii$
  2. $a - iv, b - iii, c - i, d - ii$
  3. $a - iii, b - iv, c - ii, d - v$
  4. $a - ii, b - v, c - iii, d - i$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Oxidoreductase is a dehydrogenase which acts as an acceptor of hydrogen or electrons. 
Isomerases are class of enzymes that convert a molecule from one isomer to another isomer. 
Ligase is an enzyme that can catalyze the joining of two large molecules by forming a new chemical bond between them. 
An enzyme that forms double bonds by removing groups from a substrate other than by hydrolysis, is called lyases.
So the correct answer is B. 
Multiple choice biology enzymes classification of enzyme enzymes classification and cofactors the origin of cells and cell division

Which class of enzyme catalyzes following reaction?
$\overset { X }{ \underset { C }{ | }  } \overset { Y }{ \underset { C\longrightarrow \quad X-Y+C=C }{ | }  } $

  1. Hydrolases

  2. Lyases

  3. Ligases

  4. Isomerases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Hydrolases are biological enzymes that catalyze the hydrolysis of a chemical reaction. They usually divide larger molecules into two smaller molecules. It is a class containing more than 200 enzymes. Some common hydrolases are esterases, proteases, lipases etc.

So, the correct option is 'Hydrolases'.

Multiple choice biology enzymes classification of enzyme enzymes classification and cofactors the origin of cells and cell division

Choose the type of enzyme involved in the following reaction.


$S - G + S' \longrightarrow S + S' - G$

  1. Dehydrogenase

  2. Transferase

  3. Hydrolase

  4. Lyase

  5. Isomerase
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Based on the type of reaction catalyzed, the international union of biochemist have classified enzymes into six major classes- Oxidoreductase, Transferase, Hydrolase, Lyase, Ligase and Isomerase.
Transferase is the general name for the class of enzymes that enact the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor).