CBSE Class 10 Science Practical Skills – CO2 is Released During Respiration

CBSE Class 10 Science Practical Skills – CO₂ is Released During Respiration

BASIC BUILDING CONCEPTS
Respiration is of two types – aerobic respiration and anaerobic respiration.

1. Aerobic respiration – In this type of respiration oxygen is utilised. As a result, complete oxidation of glucose takes place and maximum amount of energy is released. This type of respiration can be represented by the following equation:
   
   Aerobic respiration involves three stages-Glycolysis, Krebs cycle and ETS. All the events associated with glycolysis occur in cytoplasm and events associated with Kreb cycle and ETS take place in mitochondria.
2. Anaerobic respiration – In this type of respiration food is oxidised in the absence of oxygen. In this case, incomplete oxidation of glucose results in release of lesser amount of energy. The process of anaerobic respiration can be represented by the following equations:
   

AIM
To show experimentally that carbon dioxide is given out during respiration,

MATERIALS REQUIRED
Conical flask, U-shaped delivery tube (tube bent twice at right angles), cotton wool or moist blotting paper, water, thread, beaker, test tube, rubber cork with one hole, 20% freshly prepared KOH solution, vaseline, soaked gram seeds.

THEORY
Respiration is a biochemical process during which food (glucose) is oxidised to liberate energy. It is a catabolic process.
In the experiment, moist gram seeds are taken as they are actively respiring and releasing CO₂. The CO₂ released is absorbed by KOH and forms KgCO₃.

PROCEDURE

1. Take about 25-30 seeds of gram and germinate these seeds by placing them on moist cotton wool or moist blotting paper for 3-4 days.
2. Place the germinated seeds into a conical flask and sprinkle a little water in flask to moist the seeds.
3. Take freshly prepared 20% KOH solution in a test tube and hang it in conical flask with help of thread.
4. Close the mouth of conical flask by placing a rubber cork containing one hole. .
5. Through the hole of rubber cork, insert one end of the U-shaped glass delivery tube in the conical flask and place the other end into a beaker filled with water.
6. Seal all the connections of the experimental set-up with vaseline so as to make it air-tight.
7. Mark the initial level of water in the U-shaped delivery tube.
8. Keep the apparatus undisturbed for 1-2 hours and note the change in level of water in the delivery tube.

OBSERVATIONS
After sometime, the level of water in U-shaped delivery tube dipped in water of the beaker rises.

RESULT
Germinated gram seeds in a conical flask release CO, during respiration. The C02 released is absorbed by KOH present in the hanging test tube in conical flask. This creates a vacuum in conical flask which causes upward movement of water in the delivery tube leading to change in level of water in the delivery tube.

PRECAUTIONS

1. Germinating seeds should be kept moist.
2. All connections of the set-up should be air-tight.
3. Freshly prepared KOH solution should be used.
4. Keep one end of U-shaped delivery tube in conical flask and the other end immersed in water of the beaker.
5. The test tube containing KOH should be hung carefully.

INTERACTIVE SESSION

Question 1.
What is respiration?
Answer:
Respiration is a biochemical process by which food material is broken down by cells into simple substances such as C02 and energy is released in the process.

Question 2.
What are the types of respiration?
Answer:
The types include-

• Aerobic respiration- Occurs in presence of O₂ and end products are CO, and H₂O.
• Anaerobic respiration- Occurs in absence of O₂ and involves incomplete oxidation.

Question 3.
What is energy output in anaerobic respiration and why is it less than the aerobic respiration?
Answer:
Anaerobic respiration releases 2 ATP, whereas aerobic respiration releases 38 ATP. It is because aerobic respiration involves complete oxidation or breakdown of glucose whereas in anaerobic respiration partial breakdown or oxidation of glucose takes place.

Question 4.
Name the steps involved in aerobic respiration.
Answer:
Steps include : Glycolysis —–> Krebs cycle ——> ETS and Oxidative phosphorylation.

Question 5.
Where do the following reactions occur in a cell – Glycolysis and Krebs cycle?
Answer:
Glycolysis – Cytoplasm of cell
Krebs cycle – Mitochondria.

Question 6.
Name the energy currency of cell.
Answer:
ATP (Adenosine triphosphate).

Question 7.
Does respiration occur in plants along with photosynthesis?
Answer:
Yes, plants also respire during day along with photosynthesis.

Question 8.
What is Compensation Point?
Answer:
Compensation Point is when the rate of photosynthesis is just equivalent to the rate of respiration so that there is no net gaseous exchange.

Question 9.
Why should the seeds be kept moist during the experiment?
Answer:
Germinating seeds require water for growth. If moisture is not available, the seeds dry up, and rate of respiration would fall.

Question 10.
What would happen if instead of moist germinating seeds, boiled seeds are used for experiment?
Answer:
Boiled seeds do not respire and hence, no result will be obtained.

Question 11.
How does the use of KOH help to show that C02 is released during respiration in the above experiment?
Answer:
KOH solution absorbs the CO₂ released during respiration of seeds, which creates a partial vacuum in the conical flask, causing the rise in the water level of the U-shaped delivery tube. Rise in the level of water shows that CO₂ is released during respiration.

Question 12.
What would happen if test tube containing KOH solution is removed from the conical flask in the set-up?
Answer:
CO₂ released during respiration of seeds will not be absorbed and there will be no rise in the level of water.

Question 13.
Why is vaseline used in the experiment?
Answer:
Vaseline is involved in all the joints in the experimental set-up, thereby making the set-up air-tight.

Question 14.
Suggest an alternate set-up for the experiment to show that CO₂ is released during respiration.
Answer:
Instead of plain water in beaker, lime water can be used. Lime water turns milky with CO₂.

Question 15.
Name the gas absorbed by KOH solution.
Answer:
CO₂

Question 16.
CO₂ is called respiratory gas. Why?
Answer:
Gases involved during respiration are called respiratory gases. They include CO₂ and O₂.

Question 17.
Write an equation to represent aerobic respiration.
Answer:
C₆H₁₂O₆ + 6O₂ ——> 6CO₂ + 6H₂O + 38 ATP

Question 18.
What is fermentation?
Answer:
The anaerobic respiration carried out by some microorganisms in called fermentation.

Question 19.
Give the end products of anaerobic respiration occurring in muscles in humans.
Answer:
Lactic acid and energy (2 ATP).

Question 20.
Why is respiration called a catabolic process?
Answer:
Respiration involves the breakdown of big molecules (e.gcarbohydrates or fats) to smaller molecules.

Question 21.
At what time of the day does plants respire?
Answer:
Plants respire all the time.

Question 22.
Define breathing.
Answer:
Breathing is a physical process of inhalation ( taking in) of oxygen-rich air and exhalation (giving out) of carbon dioxide-rich air.

NCERT LAB MANUAL QUESTIONS

Question 1.
What is the role of KOH in this experiment?
Answer:
KOH absorbs the CO₂ released by germinating seeds leading to creation of partial vacuum.

Question 2.
When we say that plants and animals respire, where exactly is the process occurring?
Answer:
Mitochondria of the cell.

Question 3.
Why do we use germinating seeds in this experiment?
Answer:
Germinating seeds respire actively at a faster rate.

PRACTICAL BASED QUESTIONS

Multiple Choice Questions/VSA (1 Mark)

Question 1.
The diagram given below is the experimental set-up to show that carbon dioxide is given out during respiration. In this set-up what does the test tube marked (X) contain? [AI 2010]

(a) Water
(b) Lime water
(c) Potassium hydroxide
(d) Hydrochloric acid

Question 2.

In the experimental set-up shown above, KOH solution has been kept in the flask to [CBSE 2012] [Delhi 2010, 2008 & 2007, AI 2009, CBSE Sample Paper 2009]
(a) react with water to generate oxygen.
(b) create a dry atmosphere for wet germinating seeds.
(c) absorb carbon dioxide so as to create a partial vacuum.
(d) remove impurities present in the air in the flask.

Question 3.
The following experiment was set-up to show that a gas is given out during respiration. But there was no rise in the level of water. This was because [CBSE 2011][AI2008 & 2007]

(a) germinating seeds have not been kept under water in the flask
(b) water is kept in the beaker instead of limewater
(c) the cork on the flask is made of rubber
(d) no substance is kept in the flask to absorb the gas given out by the seeds

Question 4.
The material used to make connections of the set-up air-tight is
(a) vaseline
(b) oil
(c) wax
(d) glue

Question 5.
Name the cell components required for completion of aerobic respiration in a cell.
(a) Chloroplast and nucleus
(b) Ribosomes and ER
(c) Golgi body and lysosomes
(d) Cytoplasm and mitochondria

Question 6.
A student used boiled seeds to perform the experiment ‘CO₂ is released during respiration’. His observation would be

(a) water level in the bent tube rises
(b) water level in the bent tube decreases
(c) water level in the bent tube remains same
(d) rise in water level depends on extent of boiling.

Question 7.
Before setting up an experiment to show that seeds release carbon dioxide during respiration, the seeds should be [AT 2007C]
(a) dried completely
(b) boiled to make them soft
(c) soaked in vinegar
(d) kept moist till they germinate

Question 8.
An experimental set-up to demonstrate respiration in germinating seeds is shown below. It is observed that water from the beaker has not risen into the delivery (bent) tube. This is because [AI 2007C]

(a) the set-up is airtight
(b) the beaker has coloured water
(c) carbon dioxide is not being absorbed
(d) no oxygen is available to seeds for respiration

Question 9.
Out of the following collections of items, which collection is required to set-up the experi¬ment, “to show that CO₂ is given out during respiration”? [Foreign 2008]
(a) Flask, beaker, delivery tube, rubber stopper, germinating seeds, water and KOH
(b) Flask, beaker, delivery tube, rubber stopper, germinating seeds, water and HCl
(c) Flask, beaker, delivery tube, rubber stopper, water and KOH
(d) Flask, beaker, delivery tube, cotton plug, germinating seeds, water and KOH

Question 10.
In plants, when the rate of photosynthesis equals the rate of respiration, it is called
(a) boiling point
(b) transpiration
(c) compensation point
(d) freezing point

Question 11.
In an airtight experimental set-up which was used by you in the laboratory to study respiration in germinating seeds, the seeds obtained the oxygen for respiration from [AI 2007C]
(a) air in the flask
(b) water in the beaker
(c) water in the germinating seeds
(d) water used for soaking the seeds

Question 12.
In the experiment “to demonstrate that CO₂ is given out during respiration”, what would you observe in the delivery tube dipped in water ? [Delhi, AI 2008C, Foreign 2008]
(a) Water level rises in the delivery tube.
(b) Water turns milky and rises in the delivery tube.
(c) Water turns milky but does not rise in the delivery tube.
(d) Water level in the delivery tube remains unchanged.

Question 13.


Four students use the experimental set-ups shown above. The set-up that would show that “carbon dioxide is given out during respiration” is
(a) I
(b) II
(c) III
(d) IV

Question 14.
An experimental set-up is given below to demonstrate that CO₂ is given out during respiration.

Four students made the following observations marked I, II, III and IV:
I. Level of water remained the same in both the beaker and the delivery tube.
II. Level of water increased in the delivery tube.
III. Level of water gets reduced in both the beaker and the delivery tube.
IV. Water ascends into the delivery tube and back flows into the beaker.
Which one of the above is the correct obser-vation?
(a) I
(b) II
(c) III
(d) IV

Question 15.
After performing the experiment to show that germinating seeds give out carbon dioxide during respiration, students drew the following diagrams.
The correct labelled diagram is

Question 16.
Out of the four experimental set-ups shown below, which one will demonstrate the evolution of carbon dioxide during respiration of germinating seeds?

(a) I
(b) II
(c) III
(d) IV

Question 17.
Which of the following precautions are to be taken for a successful run of the experiment to show that carbon dioxide is given out during respiration ?
A. Cork should be airtight.
B. Seeds in the flask should be totally dry.
C. A small tube with freshly prepared KOH solution should be placed in the flask.
D. The end of the delivery tube should be above water level.
The correct answer is
(a) A and B
(b) A and C
(c) A, B and C
(d) A, B and D

ANSWER KEY

1. (c)
2. (c)
3. (d)
4. (a)
5. (d)
6. (c)
7. (d)
8. (c)
9. (a)
10. (c)
11. (a)
12. (a)
13. (d)
14. (b)
15. (d)
16. (d)
17. (b)

Short Answer Questions

Question 1.
What is respiration? Why is respiration a catabolic process?
Answer:
Respiration is a biochemical process in which food material is broken down into simple substances, like carbon dioxide and energy is released. Respiration involves breakdown of larger molecular (carbohydrates and fats) into smaller molecules. Hence, it is a catabolic process.

Question 2.
Differentiate between aerobic and anaerobic respiration.
Answer:

Question 3.
What would happen if:

1. KOH solution is not hung in conical flask during experiment.
2. seeds are not kept moist during experiment.

Answer:

1. Carbon dioxide released by respiration of seeds will not be absorbed. So, partial vacuum will not be created and thus there will be no rise in the level of water in the glass tube.
2. If moisture is not available, seeds will dry up and rate of respiration would fall.

Question 4.
Why are germinating seeds taken in the experiment? What would happen if germinating seeds are replaced by boiled seeds?
Answer:
As germinating seeds respire actively and at a faster rate, they are taken for the experiment. Boiled seeds do not respire and so no results will be obtained if they replace the germinating seeds in the experiment.

Question 5.
What happens to carbon dioxide given out by germinating seeds while performing the experiment?
Answer:
The carbon dioxide given out by germinating seeds is absorbed by KOH and potassium carbonate is formed.

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