2.3.6 Investigating Plant Root Tips

Key Steps in Investigating Plant Root Tips:

1. Preparing the Sample:

• Use root tips (e.g., from garlic or onion) as these contain actively dividing cells.
• Cut the root tips (about 1–2 mm) from the growing end where mitosis occurs.

2. Fixing the Root Tips:

• Place the root tips in a fixative solution (e.g., acetic alcohol) to preserve the cells and prevent further division.

3. Staining:

• Stain the root tips with a dye such as toluidine blue or acetic orcein, which binds to chromosomes and makes them visible under the microscope.

4. Softening the Tissue:

• Heat the root tips gently in acid (e.g., hydrochloric acid) to break down the cell walls and allow the cells to spread more easily.

5. Mounting the Root Tip:

• Place the stained root tip on a microscope slide.
• Use a mounted needle to gently squash the tissue, spreading the cells into a single layer to observe individual nuclei and chromosomes.

Observing Under the Microscope:

• Use a light microscope to view the prepared slide.
• Identify cells in different stages of mitosis: prophase, metaphase, anaphase, and telophase.
• Record your observations with labelled diagrams.

Calculating the Mitotic Index:

• The mitotic index is the proportion of cells undergoing mitosis and is calculated using the formula:

$$\text{Mitotic Index} = \frac{\text{Number of cells in mitosis}}{\text{Total number of cells observed}} \times 100$$

• A higher mitotic index indicates a higher rate of cell division, typical in growing tissues.

Safety Precautions:

• Wear gloves and safety goggles when handling stains and acids.
• Use care when cutting root tips and handling sharp objects (e.g., needles and scalpel).

Applications of Root Tip Investigation:

• Study cell division and the stages of mitosis in plants.
• Compare mitotic activity in different plants or conditions (e.g., varying nutrient levels or light exposure).