Cellular Respiration Grade 11 pdf Questions and Answers:

Important Terminologies for Cellular Respiration Grade 11:

Cellular respiration is a crucial biological process that occurs within cells, facilitating the conversion of glucose into energy in the form of adenosine triphosphate (ATP). Here, we’ll expand on several key components and steps involved in cellular respiration, particularly relevant to the Grade 11 curriculum:

  • Cellular Respiration: This is the process by which cells extract energy from carbohydrates, primarily glucose, to produce ATP. It involves several stages including glycolysis, the Kreb’s Cycle, and the electron transport chain, and it occurs within the mitochondrion.
  • Kreb’s Cycle: Also known as the citric acid cycle, this is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins into carbon dioxide. It also generates high-energy molecule stores such as NADH and FADH2, which are used in the electron transport chain.
  • Oxygen: Essential for aerobic respiration, oxygen acts as the final electron acceptor in the electron transport chain, combining with electrons and hydrogen ions to form water. This process releases a significant amount of energy, which is used to synthesize ATP.
  • Aerobic Respiration: This type of respiration requires oxygen and includes glycolysis, the Kreb’s Cycle, and the electron transport chain. It is highly efficient and produces up to 38 ATP molecules from a single glucose molecule.
  • Ethanol: In anaerobic conditions, some organisms, like yeast, convert pyruvate (produced in glycolysis) to ethanol and carbon dioxide. This process is known as alcoholic fermentation and is used in brewing and baking industries.
  • Glycolysis: The first step in both aerobic and anaerobic respiration, glycolysis occurs in the cytoplasm of the cell where glucose is broken down into two molecules of pyruvate, producing a small yield of ATP and NADH.
  • Anaerobic Respiration: This process occurs without oxygen. It is less efficient than aerobic respiration and results in the production of lactic acid or ethanol, depending on the organism, along with a minimal amount of ATP.
  • Lactic Acid: Produced in muscle cells during rapid exercise when oxygen is scarce, pyruvate is converted into lactic acid. This can lead to muscle fatigue and soreness but is also a quick way to produce ATP.
  • Mitochondrion: Known as the powerhouse of the cell, mitochondria are organelles that host most of the biochemical processes of cellular respiration, particularly the Kreb’s Cycle and the electron transport chain.
  • Co-enzyme: Co-enzymes are non-protein molecules that assist enzymes in their catalytic activity. Important co-enzymes in cellular respiration include NAD+ and FAD, which are reduced to NADH and FADH2 during different stages of respiration to carry electrons to the electron transport chain.
  • Carbon Dioxide: A by-product of the Kreb’s Cycle, carbon dioxide is formed during the decarboxylation of intermediate compounds in the cycle. It is expelled from the body through the respiratory system.
  • ATP (Adenosine Triphosphate): The main energy currency of the cell, ATP is produced during various stages of cellular respiration, with the majority generated during the electron transport chain through a process called oxidative phosphorylation.

Each of these components plays a vital role in cellular respiration, ensuring that cells receive the necessary energy to function. This topic is fundamental in Grade 11 biology, as it relates to both cellular processes and broader physiological functions.

Cellular Respiration Grade 11 Questions and Answers with Exam Tips

What is cellular respiration?

Answer: Cellular respiration is a metabolic process in which cells convert nutrients, primarily glucose, into ATP (adenosine triphosphate) and waste products, using oxygen. It allows cells to extract energy from food molecules.

Exam Tip: Be sure to emphasize the role of oxygen in cellular respiration and distinguish it from anaerobic processes where oxygen is absent.

List the three main stages of cellular respiration and briefly describe what happens in each.


  • Glycolysis: Glucose is broken down into two molecules of pyruvate, yielding 2 ATPs and 2 NADH molecules.
  • Krebs Cycle: Pyruvate is further broken down in the mitochondria to produce ATP, NADH, and FADH2, releasing carbon dioxide as a waste product.
  • Electron Transport Chain: Electrons from NADH and FADH2 pass through a chain of proteins in the mitochondrial membrane, creating a gradient that generates ATP.

Exam Tip: Make sure to understand the inputs and outputs of each stage—knowing what each process starts with and what it produces is critical for solving related exam questions.

Explain the role of glucose in cellular respiration.

Answer: Glucose serves as the primary fuel molecule for cellular respiration. It enters glycolysis where it is broken down to generate ATP and electron carriers, which are used in further stages to produce a significant amount of ATP.

Exam Tip: Highlight the energy transformations from glucose to ATP and the efficiency of glucose utilization in your answers.

Describe what happens during glycolysis.

Answer: During glycolysis, one glucose molecule (6 carbons) is converted into two molecules of pyruvate (3 carbons each), producing a net gain of 2 ATP molecules and 2 NADH molecules. This process occurs in the cytoplasm of the cell.

Exam Tip: Remember that glycolysis does not require oxygen, which is a key point when discussing cellular energy processes under anaerobic conditions.

What is the Krebs cycle and why is it important in cellular respiration?

Answer: The Krebs cycle, also known as the citric acid cycle, occurs in the mitochondria and processes the byproducts of glycolysis to produce ATP, NADH, and FADH2, along with carbon dioxide. It is crucial because it supplies the high-energy electrons needed to power the electron transport chain.

Exam Tip: Be prepared to discuss the cyclic nature of the Krebs cycle and how it connects to other metabolic pathways.

Explain the electron transport chain and its function.

Answer: The electron transport chain is a series of proteins located in the inner membrane of the mitochondria. It uses electrons from NADH and FADH2 to pump protons across the membrane, creating a gradient. The flow of protons back through ATP synthase generates ATP.

Exam Tip: Focus on the flow of electrons and the generation of a proton gradient as these are central to understanding how ATP is produced in this stage.

How is ATP generated in cellular respiration?

Answer: ATP is generated in cellular respiration through substrate-level phosphorylation during glycolysis and the Krebs cycle, and by oxidative phosphorylation during the electron transport chain. The latter produces the majority of ATP in this process.

Exam Tip: Distinguish between substrate-level phosphorylation and oxidative phosphorylation in your explanations, as this distinction often comes up in exams.

What are the end products of aerobic cellular respiration?

Answer: The end products of aerobic cellular respiration are carbon dioxide, water, and ATP. Carbon dioxide is expelled as a waste product, while ATP is used as the energy currency of the cell.

Exam Tip: Understand the importance of oxygen in producing water and how it differs from the products of anaerobic respiration.

Compare and contrast aerobic and anaerobic respiration.

Answer: Aerobic respiration requires oxygen and produces a high yield of ATP by fully oxidizing glucose into carbon dioxide and water. Anaerobic respiration does not require oxygen and generally produces less ATP by partially breaking down glucose into products like lactate or ethanol.

Exam Tip: Be prepared to provide examples of conditions or organisms where anaerobic respiration is utilized.

What happens during fermentation? Explain the types of fermentation and their products.

Answer: Fermentation occurs when oxygen is not available. It allows cells to continue producing ATP through glycolysis by regenerating NAD+. There are two main types:

  • Lactic acid fermentation: Produces lactate and is used by muscle cells and some bacteria.
  • Alcoholic fermentation: Produces ethanol and carbon dioxide, used by yeasts and some types of bacteria.

Exam Tip: Focus on the differences in byproducts and the organisms that use each type of fermentation, as these are key details frequently tested.

Give the correct biological term for each of the following descriptions. Write only the term next to the question numbers in the answer book. 

Breaking down of glucose (organic compounds) so as to gradually release energy to all cells

Process of cellular respiration that takes place in the presence of O2
Aerobic respiration

Process of cellular respiration that takes place in the absence of O2 OR Biochemical pathway taken by the process of cellular respiration in the absence O2
Anaerobic respiration

The non-protein partner that are carriers of high energy Hydrogen atoms in the oxidative phosphorylation stage of respiration. OR Organic compounds that act as Hydrogen acceptors / carriers during cellular respiration

An energy carrier
ATP (Adenosine Triphosphate)

The gas needed/ required for the process of cellular respiration OR The final acceptor of Hydrogen atoms

Stage of cellular respiration that takes place in the cytoplasm/ cytosol OR Anaerobic phase of respiration that occurs in the cytosol

The organelle in a cell at which Kreb’s cycle occurs

Cyclic series of reactions that takes place in the mitochondrion OR Phase of cellular respiration in which CO2 is evolved OR Phase of respiration which releases a large amount of energized hydrogen atoms.
Kreb’s Cycle

Product, other than CO2 of alcoholic fermentation in plants OR Organic product of anaerobic respiration in plants.

Organic acid builds up in the muscle cells due to anaerobic respiration
Lactic acid

Is a gas given off as a by-product during the process of cellular respiration? OR Gas evolved during process of cellular respiration
Carbon dioxide

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