Biology experiment - Experiment Showing that Carbon Dioxide is Given out During Respiration
When you think of the word 'respire', you probably think of breathing. In breathing, you are taking in oxygen and releasing carbon dioxide. This gaseous exchange is important for respiration, but while breathing is a physical process, respiration is more of a chemical process. All organisms, from a single bacterial cell to plants to a blue whale, undergo respiration.
Respiration takes place in all types of living cells, and it’s called cellular respiration. Energy stored in glucose is released during respiration and without it, these cells would die. There are two types of respiration:
Aerobic respiration occurs in the presence of oxygen, in most cells most of the time.
Anaerobic respiration occurs without oxygen.
Some of the energy liberated during the breakdown of the glucose molecule is in the form of heat, but a large part of heat energy is converted into chemical energy released by these ATP molecules.
Table of Content
Aim
Theory
Material Required
Procedure
Observation
Results
Precautions
Aim
To experimentally show that carbon dioxide is given out during respiration.
Theory
Living organisms obtain their energy from the food material by the method of cellular respiration. Most of the organisms are aerobic wherein, oxygen is used to break-down glucose entirely into carbon dioxide and water and simultaneously release energy in the process. Organisms like yeast and certain bacteria can respire in the absence of oxygen by a process known as anaerobic respiration. In this process, glucose is converted to ethanol, and carbon dioxide and energy are released. This process of respiration in some microorganisms under oxygen depriving conditions is called fermentation. In this experiment, we are going to study the process of fermentation and the liberation of heat and carbon dioxide gas.
Materials Required
Test tube
Delivery tube
Yeast
Sugar solution
Paraffin wax
Lime water
Thermometer
Thermos flask
Procedure
Step 1. Take some sugar solution in a test tube and keep it for a minute to remove the oxygen in it and cool it.
Step 2. Pour this sugar solution into the thermo flask.
Step 3. Add some yeast to the sugar solution.
Step 4. The presence of oxygen in the solution can be tested by adding a few drops of diazin green to the solution. The blue colour solution of diazin green turns pink if oxygen is absent in the solution.
Step 5. Pour liquid paraffin into the solution.
Step 6. Insert the thermometer and one end of the delivery tube into the Thermos flask and another end of the delivery tube into the conical flask containing lime water (as shown in the image).
Step 7. Leave the experimental set-up for 2 hours. Observe the mercury level of the thermometer and the appearance of lime water.
Experimental setup showing that carbon dioxide and heat are liberated during respiration
Observations
After two hours, we observe that the mercury level has risen due to the release of heat and the lime water turned milky white due to the absorption of carbon dioxide.
Result
The increase in the level of mercury in the thermometer indicates that carbon dioxide is produced during anaerobic respiration. The yeast respire and produce carbon dioxide, which is absorbed by the lime water and creates a milky appearance.
Precautions
There should be no air gaps while pouring paraffin wax.
Keep the conical flask clean.
Fix the end of the delivering tube in a Thermo flask so it becomes airtight.
Use freshly prepared lime water solution.
Lab Manual Questions
What is the difference between aerobic and anaerobic respiration?
Ans: The differences between these two types of respiration are listed below:
Aerobic respiration: It is the breakdown of glucose in the presence of oxygen.
Anaerobic respiration: It is the breakdown of glucose in the absence of oxygen.
What is the role of lime water in this experiment?
Ans: Lime water solution absorbs the CO2 released during respiration and creates white turbidity.
How can you prove that heat is liberated during respiration?
Ans: The increase in the level of mercury in the thermometer indicates that carbon dioxide is produced during respiration.
Why do we use yeast in this experiment?
Ans: Yeasts undergo fermentation and convert carbohydrates into carbon dioxide.
Viva Questions
1. What is respiration?
Ans: The process of breakdown of food in the cell with the release of energy is called respiration.
2. What are the types of respiration?
Ans: There are two types of respiration: Aerobic and Anaerobic respiration.
3. What is anaerobic respiration?
Ans: When Respiration takes place in the absence of oxygen, it is known as anaerobic respiration. This process is also called fermentation.
4. What is the end product of anaerobic respiration?
Ans: The end products of anaerobic respiration are carbon dioxide, ethanol, and ATP molecules.
5. Name the energy currency of the cell.
Ans: The energy currency of the cell is ATP molecules.
6. Name two respiratory mediums for living beings.
Ans: Air and water are the two respiratory mediums.
7. Name some industrial products of fermentation.
Ans: Acetic acid, Citric acid, and Ethanol are products of fermentation.
8. Define RQ.
Ans: The RQ is the ratio of carbon dioxide production to oxygen consumption.
9. How does the use of lime water help to show that carbon dioxide is released during respiration in the above experiment?
Ans: Lime water solution absorbs the carbon dioxide released during respiration and creates white turbidity.
10. Why is less energy released during anaerobic respiration?
Ans: Because the glucose molecules are partially broken down.
Practical Based Questions
Anaerobic respiration is
Intramolecular respiration
Molecular respiration
Intermolecular respiration
Intra-molecular respiration
Ans: D. Intra-molecular respiration
Anaerobic respiration is also called as
Fermentation
Respiration
Aerobic respiration
None of them
Ans: A. Fermentation
Which of the following processes is common for aerobic and anaerobic respiration?
Glycolysis
Krebs cycle
TCA cycle
None of these
Ans: A. Glycolysis
Which is a product of anaerobic respiration?
Pyruvic acid
Citric acid
Ethyl alcohol/lactic acid
None of the above
Ans: C. Ethyl alcohol/lactic acid
R.Q. of anaerobic respiration is:
Zero
Infinity
Less than two
More than five
Ans: B. Infinity
Which of the following physiological processes does not require water as a reactant?
Anaerobic respiration
Digestion of dietary protein
aerobic respiration
photosynthesis
Ans: A. Anaerobic respiration
Substances that yeast cannot produce by anaerobic respiration are:
CO2
Pyruvate
Lactic acid
Alcohol
Ans: C. Lactic acid
Which of the following is true for anaerobic respiration?
Glucose + lactic acid = carbon dioxide + water
Glucose= Lactic acid + carbon dioxide
Glucose gives lactic acid
None of the mentioned
Ans: C. Glucose gives lactic acid
Compared with aerobic respiration, the main characteristic of anaerobic respiration is:
Decompose organic matter
release energy
Requires enzymes to catalyse
Incomplete decomposition of organic matter
Ans: D. Incomplete decomposition of organic matter
The kind of respiration through which skeletal muscles of the human body get the energy is:
acidic respiration
anaerobic respiration
aerobic respiration
nitrogenous respiration
Ans: B. anaerobic respiration
Summary
Lime water solution absorbs the carbon dioxide released during the respiration of yeast, which creates white turbidity in the conical flask, causing a milky appearance in the lime water of the test tube. The rise in the level of mercury in the thermometer shows that heat is released during respiration.
FAQs on CBSE Biology Experiment to Show that Carbon Dioxide is Given out During Respiration
1. For 5 marks, how would you design an experiment to show that carbon dioxide is given out during anaerobic respiration in yeast as per the CBSE Class 10 syllabus for 2025-26?
To demonstrate that carbon dioxide is produced during anaerobic respiration, you can perform the following experiment:
- Aim: To prove that CO₂ is released during anaerobic respiration.
- Materials Required: A thermos flask, a test tube, a delivery tube, yeast, sugar solution, lime water (calcium hydroxide), and liquid paraffin.
- Procedure: Take some sugar solution in the thermos flask and add a small quantity of yeast to it. Cover the surface of the solution with a layer of liquid paraffin to cut off the oxygen supply. Close the flask with a cork and insert one end of a delivery tube. Place the other end of the delivery tube into a test tube containing freshly prepared lime water.
- Observation: After some time, you will observe bubbles in the lime water, and the lime water will turn milky or cloudy white. A thermometer placed in the flask would also show a slight rise in temperature.
- Conclusion: The gas released by the yeast during anaerobic respiration is carbon dioxide, which reacts with lime water to form an insoluble precipitate of calcium carbonate, making it milky. This proves that CO₂ is evolved.
2. What is the specific role of lime water in the experiment to prove CO₂ is produced during respiration, and what is the expected chemical reaction?
The specific role of lime water (calcium hydroxide, Ca(OH)₂) is to act as an indicator for the presence of carbon dioxide. When carbon dioxide gas is passed through it, a chemical reaction occurs, forming calcium carbonate (CaCO₃), which is a white, insoluble substance. This makes the clear lime water turn milky or cloudy, providing visible proof that CO₂ has been produced. The reaction is: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l).
3. A common alternative experiment uses germinating seeds to show respiration. How does this setup differ, and why is potassium hydroxide (KOH) often used in it?
In the experiment with germinating seeds, the goal is to show they consume oxygen and release CO₂. Here's how it differs and the role of KOH:
- Setup: Germinating seeds are placed in a sealed flask. A small test tube containing potassium hydroxide (KOH) solution is hung inside the flask. The flask is connected to a manometer.
- Role of KOH: Unlike lime water, which indicates CO₂, potassium hydroxide (KOH) absorbs CO₂. As the seeds respire, they use up oxygen and release CO₂. The KOH absorbs this CO₂, creating a partial vacuum inside the flask.
- Observation: This vacuum causes the water level in the manometer to rise, proving that oxygen was consumed by the seeds for respiration. This setup is primarily used to demonstrate O₂ consumption.
4. What are three important precautions a student must take to ensure the experiment to show CO₂ evolution is successful and accurate?
For accurate results in this experiment, a student should take the following precautions:
- Ensure the experimental setup is completely airtight to prevent atmospheric gases from interfering with the results.
- Use freshly prepared lime water, as old lime water may have already reacted with atmospheric carbon dioxide, making it less effective.
- When using yeast, ensure a layer of liquid paraffin is properly added to cover the sugar solution, effectively cutting off the oxygen supply to ensure anaerobic respiration occurs.
5. Why is it important to use a thermos flask in the yeast fermentation experiment? What two metabolic signs can be observed with this setup?
A thermos flask is important because it is an insulator. Respiration is an exothermic process, meaning it releases energy as heat. A thermos flask prevents this small amount of heat from escaping, allowing a thermometer to detect a noticeable rise in temperature. Therefore, this setup helps observe two key metabolic signs:
- The production of heat energy (detected by a thermometer).
- The production of carbon dioxide (detected by passing the evolved gas through lime water).
6. From an exam perspective, what is the key difference between the end products of anaerobic respiration in yeast and in human muscle cells during strenuous exercise?
This is a critical distinction for board exams. While both are types of anaerobic respiration, their end products differ:
- In Yeast (Fermentation): Glucose is broken down into Ethanol (C₂H₅OH), Carbon Dioxide (CO₂), and a small amount of energy (2 ATP).
- In Human Muscle Cells: During intense exercise when oxygen is scarce, glucose is broken down into Lactic Acid and a small amount of energy (2 ATP). Carbon dioxide is not produced in this specific pathway.
7. If a student performs the yeast experiment but forgets to add the layer of paraffin wax, how would this mistake affect the outcome and the conclusion?
Forgetting the paraffin wax layer would be a critical error. The paraffin is meant to cut off the oxygen supply, creating anaerobic conditions. Without it, oxygen from the air can dissolve in the sugar solution. The yeast would then perform aerobic respiration, which is much more efficient. While CO₂ would still be produced (and turn lime water milky), the experiment would fail to demonstrate anaerobic respiration. The end products would be primarily carbon dioxide and water, not the ethanol characteristic of fermentation.
8. Why is significantly less energy released during anaerobic respiration compared to aerobic respiration?
Less energy is released during anaerobic respiration because the breakdown of the food substance (glucose) is incomplete. In the absence of oxygen, glucose is only partially oxidised into smaller molecules like ethanol or lactic acid, which still contain a large amount of chemical energy. In contrast, aerobic respiration involves the complete oxidation of glucose into carbon dioxide and water, releasing all its stored energy (approximately 38 ATP compared to 2 ATP in anaerobic respiration).
