As we know that plants exchange gases through stomata, carbon dioxide and oxygen are exchanged by diffusion here. These gases can either enter cells or escape into the atmosphere.
  • The development of a potassium ion gradient is required for stomatal opening and closing.
  • The guard cells use ATP created during photosynthesis to transfer potassium ions from nearby cells into the guard cells.
  • When the concentration of \(K^+\) ions in the guard cells rises, the cells become hypertonic, and more water moves into the cells.
  • As a result, the guard cells thicken, increasing the stomatal aperture.
The opening and closing of stomata.
The differences between a monocot and dicot stomata can be studied with this experiment (refer page 93).
An experiment to show CO2 is liberated during the respiration:
To understand that carbon dioxide is the gas that is liberated during the process of cellular respiration.
Materials required:
Germinating gram seeds, petroleum jelly, \(100 mL \)conical flask, KOH solution, \(250 mL \)beaker, a bent clean delivery tube, single-bore cork, small test tube, measuring scale and a piece of thread.
  • In a conical flask, take about forty germinating seeds.
  • Using the cork, fix the mouth of the conical flask with the help of a thread and suspend the tube containing the KOH solution.
  • Place one end of a clean delivery tube through the cork of the conical flask. Then, as illustrated, dip the opposite end of the delivery tube into a beaker of water. We can see a rise in the level of water inside the delivery tube at the end dipped in the water due to capillary action. Mark this as the initial reading (\(h1\)) of the water level in the delivery tube.
  • Apply a thin smear of petroleum jelly to the conical flask to make it airtight so that the gas evolved during the germinating seeds' respiration process does not escape and place the apparatus undisturbed for about \(45\)minutes under the sunlight.
  • Look out for changes in the water level inside the delivery tube after forty-five minutes. If there are changes, note and record the final water level (\(h2\)) in the delivery tube.
Experimental setup
After \(2\)hours, it was noticed that the water level in the U-shaped delivery tube dipped in the beaker had risen above the initial marked level.
Results and discussion:
During respiration, germinating seeds in the conical flask release CO2, which is absorbed by KOH kept in a small tube. The absorption of CO2 creates a vacuum in the flask, causing the level of water in the delivery tube to rise.
Another method can be used to demonstrate that CO2 is released during plant respiration (refer page number 103).