Lab Manual: CO2 is Released During Respiration | Lab Manuals for Class 10 PDF Download

Objective

Theory/Principle

1. Aerobic
2. Anaerobic

1. Aerobic Respiration
It is the respiration process occurring in the presence of oxygen. A complete oxidation of glucose (carbohydrates) takes place releasing carbon dioxide gas, water and a large amount of energy in the form of ATP (i.e. adenosine triphosphate) during this process.
The reaction of this process is represented by the following equation:

2. Anaerobic Respiration
It is the respiration process occurring in the absence of oxygen. It leads to incomplete oxidation of organic food (glucose) releasing carbon dioxide and ethyl alcohol and a very less/insignificant amount of energy. It is more commonly called as fermentation in micro-organisms.
The reaction of this process is represented by the following equation:
In this experiment to show that CO₂ is released during respiration, moist gram seeds are used as they are actively respiring and release CO₂.
The released CO₂ is absorbed by KOH and forms K₂CO₃ (Method 1).
Also, CO₂ can cause lime water to change its appearance (Method 2).

Materials Required
A conical flask, soaked and germinating seeds of gram, 20% freshly prepared KOH (potassium hydroxide) solution, vaseline, U-shaped delivery tube (a tube bent twice at right angles), moist cloth (cotton/wool or moist blotting paper), water, thread, beaker, test tube and a rubber cork with one hole.

Procedure

• Take about 30-40 seeds of gram soaked in water and allow them to germinate by placing them on a moist cotton/wool or blotting paper or moist cloth for 2-5 days.
• Transfer the germinating seeds (seeds with a whitish outgrowth) into a conical flask and add few drops of water to keep the seeds moist.
• Take the freshly prepared solution of 20% KOH in a test tube and suspend it in the conical flask using a thread just above the germinating seeds.
• The mouth of the conical flask is closed by placing the rubber cork with one hole. Ensure that the thread tied to KOH containing tube is firmly placed and held at a correct distance.
• Take the U-shaped delivery tube, insert one of its end in the conical flask through the hole in the rubber cork. The other end of the delivery tube is placed in a beaker containing water.
• Seal all the connections of the experimental set up (Fig. 1) with vaseline (petroleum jelly) to make the apparatus airtight.
  
• Mark the initial level of water in the delivery tube and leave the set up undisturbed for 1-2 hours.
• Observe the change in the level of water in the delivery tube immersed in water inside the beaker.

Observations

• After 2 hours, it was observed that the level of the water has risen up in the U-shaped delivery tube dipped in the beaker from the initial marked level (Fig. 2).
• Germinating seeds in the conical flask release CO₂ during respiration which is absorbed by KOH kept in small tube. Due to the absorption of CO₂ a vacuum is created in the flask which causes the rise in level of water in the delivery tube.
• Another method can also be used to show that CO₂ releases during respiration by plants.
  

Materials Required
Germinating gram seeds, lime water or phenol red indicator, vaseline, a thistle funnel, a delivery tube, a rubber tubing, rubber cork with two holes, conical flask and a boiling tube.

Procedure

• Place about twenty germinating seeds in a boiling tube containing some water in it.
• Fit a two-bore rubber cork to the mouth of the boiling tube. Make the set up air-tight by applying a thin smear of petroleum jelly so that the gas evolved during the process of respiration by the germinating seeds does not leak out.
  
• Fix a thistle funnel through one of the bores in the cork. The lower end of thistle funnel must dip in water.
• Pass a delivery tube through the second bore of the cork, Attach a rubber tubing to the delivery tube, fold it backwards and fix a pinch cock. Using a clamp, fix the boiling tube to a stand as shown in Fig. 3.
• Place the set up in bright sunlight for about one hour.
• Takeaboutl mLof water in a test tube (1 drop of water has a volume of nearly 0.1 ml).Add two drops of phenol red indicator to it and shake. Note the colour.
• Dip the free end of rubber tubing into the test tube containing phenol red indicator solution and release the pinch cock.
• Pour a few mL of water through the thistle funnel into the boiling tube containing germinating gram seeds.
• Observe bubbles of a gas emerging from the rubber tube dipped in the phenol red indicator solution. Shake the test tube vigorously and note the change in the colour of indicator. Record your observations.

Observations
The colour of phenol red indicator changes from pink (in neutral/alkaline medium) to pale yellow (in acidic medium) due to the addition of carbon dioxide in it.

Result
The germinating seeds of gram performs active respiration and release CO₂ which can be – seen as:

• The increased level of water in the U-shaped delivery tube in method 1
• Colour change of’ phenol red from pink colour to pale yellow in method 2.
  Thus, it is confirmed that respiration in plants releases CO₂.

Precautions

• Germinating seeds should be kept moist at all times.
• All the experiment setup connections must be air tight.
• Freshly prepared KOH solution must be used. KOH is corrosive, handle it carefully
• The end of the delivery tube present in the beaker In both methods should be completely immersed in water/lime water.
• Lime water should be freshly prepared for experimental use.