Iodine solution is a chemical reagent used in microscopy to identify the presence of starch grains in plant cells. This staining technique allows starch-containing structures to be easily observed under the microscope.

Key Points:

1. Preparation of Specimen:

• A thin section of the plant tissue is prepared and placed on a slide.
• A drop of iodine solution is added to the tissue to stain the starch grains.
• The slide is covered with a coverslip and observed under a light microscope.

2. Location of Starch Grains:

• Found in amyloplasts within plant cells.
• Commonly observed in tissues such as:
• Storage organs (e.g., potato tubers).
• Leaves, where starch is temporarily stored during photosynthesis.

3. Detection of Starch:

• When iodine binds to starch grains, the grains turn blue-black.
• The colour change is due to the formation of an iodine-starch complex.

4. Iodine as a Staining Agent:

• Iodine is dissolved in potassium iodide solution to create the reagent.
• The solution interacts with starch, causing a colour change.

Tip for Exams:

• Understand the blue-black colour change as a key indicator of starch presence.
• Be able to describe how to prepare a slide and use iodine solution in practical questions.
• Link the detection of starch grains to biological processes such as photosynthesis and storage.

Summary:

• Iodine solution is used to detect starch grains, which stain blue-black.
• This method is vital for identifying storage structures in plants and linking starch presence to physiological functions.