$(a)$ List the three events that occur during the process of photosynthesis. Explain the role of stomata in this process.
$(b)$ Describe an experiment to show that sunlight is essential for photosynthesis.

(N/A) The three events that occur during the process of photosynthesis are:
$(i)$ Absorption of light energy by chlorophyll.
(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to carbohydrates.
Role of stomata: Stomata help in the gaseous exchange between the plant and its atmosphere. They facilitate the intake of carbon dioxide, which is essential for photosynthesis.
$(b)$ Experiment to show sunlight is essential for photosynthesis:
$1$. Place a healthy potted plant in a dark room for $1-2$ days to destarch the leaves.
$2$. Cover a portion of a leaf on both sides with black paper strips using paper clips.
$3$. Expose the plant to bright sunlight for a few hours.
$4$. Pluck the leaf, boil it in alcohol to remove chlorophyll (decolorize), and wash it.
$5$. Add a few drops of iodine solution to the leaf.
Observation: The portion covered with black paper does not turn blue-black, while the exposed portion turns blue-black, indicating the presence of starch. This proves that sunlight is essential for photosynthesis.