(a) (i) What is the first step in the breakdown of glucose during aerobic and anaerobic respiration? Where does it take place?

(ii) ATP is called the energy currency of the cell. Why?

(iii) What is meant by "residual volume of air" in a breathing cycle?

OR

(b) Write in sequence the steps for experimental verification of the fact that "sunlight is essential for photosynthesis".

(a) (i) The first step in the breakdown of glucose during both aerobic and anaerobic respiration is glycolysis, which involves the breakdown of a 6-carbon glucose molecule into two 3-carbon molecules of pyruvate. This process takes place in the cytoplasm of the cell.

(ii) ATP (Adenosine Triphosphate) is called the energy currency of the cell because the energy released during cellular respiration is immediately used to synthesize ATP from ADP and inorganic phosphate. When the cell needs energy to drive endothermic reactions (such as protein synthesis, muscle contraction, and nerve impulse conduction), the terminal phosphate linkage in ATP is broken using water, releasing a fixed amount of energy ($30.5\text{ kJ/mol}$).

(iii) Residual volume of air is the volume of air that always remains inside the lungs after a forceful expiration. It ensures that during the breathing cycle (inhalation and exhalation), there is always sufficient time for oxygen to be absorbed into the blood and for carbon dioxide to be released from the blood into the lungs.

OR

(b) Experimental verification that sunlight is essential for photosynthesis:

1. De-starching: Keep a healthy potted plant in a dark room for 2 to 3 days to ensure that all the starch present in its leaves is completely consumed.
2. Covering the leaf: Select a leaf on the plant and cover a portion of it on both sides with a strip of black paper using paper clips, ensuring no light can reach this covered area.
3. Exposure to sunlight: Place the potted plant in bright sunlight for 4 to 6 hours to allow photosynthesis to occur in the uncovered parts.
4. Decolorization: Pluck the leaf, remove the black paper, and boil it in water for a few minutes. Then, place the leaf in a beaker of alcohol and heat it in a water bath until the leaf loses its green chlorophyll pigment and becomes pale.
5. Washing: Wash the decolorized leaf thoroughly in warm water to remove any remaining alcohol.
6. Iodine Test: Place the leaf in a petri dish and add a few drops of iodine solution over it.

• Observation: The uncovered part of the leaf turns blue-black (indicating starch formation), while the covered part remains pale brown (indicating no starch was formed).
• Conclusion: This demonstrates that sunlight is essential for photosynthesis.