Activity 1.1 asks us to put a plant in the dark for 72 hours, test its leaf for the presence of the starch with iodine and compare the result with a plant kept in sunlight.
How do we do a test for the starch
We first put the leaf in a boiling solution of spirit. Spirit breaks the leaf cells, and all the green colour of chlorophyll goes into the spirt. We do this because the colourless leaf is easy to stain with iodine. Now we put iodine solution on the colourless leaf. If the leaf contains the starch, it turns blue.
Leaf of the plant kept in the dark does not turn blue. While the leaf of the plant remained in sunlight turns blue with iodine.
This experiment shows that the plant kept in the dark does not produce starch. Thus we can say that sunlight is essential for starch formation.
Plant prepare their food from the carbon dioxide and water in the presence of the sunlight. When we keep the plant in the dark, a plant is not able to make their food. As a result, when we put the iodine solution to that leaf, it does not turn blue. A plant kept in sunlight can make their food, so the iodine solution turns blue.
Activity 1.2 asks us to water a piece of bread, put it into a warm place and observe it.
Observation: Green and black cotton thread like mould appear on the bread.
The wet and warm place is the favourites of saprophytes. Saprophytes are the organism which obtains their nutrition from dead or decaying materials. They clean the dead materials, so they are also called ‘scavengers of the earth’. Their spores are present everywhere in the air. They settle at a damp and warm place and multiply. Bread mould is favourite of a fungus named Rhizopus. So, we also call them Bread Mould. They are a thin thread-like structure with a bulb. Bulb stores the spore, which on maturation released into the air.