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## Let Us Revise **Mark the following statements (T) if true and (F) if false.** * The air breathed in, passes from nostrils through the trachea to the pharynx. * Alveoli are the units of lungs. * In the cell, energy is obtained by breaking down sugars into carbon dioxide and water in the presence...

## Let Us Revise **Mark the following statements (T) if true and (F) if false.** * The air breathed in, passes from nostrils through the trachea to the pharynx. * Alveoli are the units of lungs. * In the cell, energy is obtained by breaking down sugars into carbon dioxide and water in the presence of oxygen. * When we inhale air, ribs move down and inwards while the diaphragm moves up. * Rib cage is an essential part of the respiratory system. ## Activity 10.2 **How do we find that carbon dioxide is released during respiration?** **Materials needed:** * A beaker * A glass tube bent at right angles at two places * A cork with a hole * Thread and coloured water * A small test tube * Potassium hydroxide solution or KOH solution * Vaseline * Germinating gram seeds **Method:** * Put some germinating gram seeds in a conical flask. * Insert the short end of the glass tube through the hole in the cork. * Before fixing the cork on the flask, suspend a tube containing KOH solution using a thread in the flask. * Take some coloured water in a beaker, and dip the longer side of the glass tube inside it. * Apply Vaseline on the rim of conical flask to prevent air from entering * Note down the initial level of water in the tube. * Keep the set up for two hours and note down the final level of water without disturbing it. **Observation:** * Water level raises in the bent glass tube **Conclusion:** * Carbon dioxide released by the seeds is absorbed by the KOH solution. * This creates a partial vacuum in the flask forcing water to rise up in the bent tube. * The rising level of water indicates that carbon dioxide during respiration.