Question

A student wanted to observe dividing cells under a microscope. The student squashed the root tip of an onion plant on a microscope slide. (i) Describe how the student should use a light microscope to view the squashed root tip. (3) (ii) Even though the slide was at the correct magnification, the student could not see the chromosomes in the dividing cells. State what could be done to the slide to make the chromosomes more visible. (1)

Answer 1

(i) To view the squashed root tip of an onion plant under a light microscope, the student should follow these steps:

1. Prepare the slide: Place a small piece of the squashed root tip onto a clean microscope slide.
2. Add a drop of stain: Apply a suitable stain, such as acetic orcein or toluidine blue, to the root tip. Stains help make cellular structures, including chromosomes, more visible.
3. Cover with a coverslip: Carefully place a coverslip over the stained root tip, ensuring there are no air bubbles.
4. Focus the microscope: Start with the lowest objective lens (usually 4x or 10x) and adjust the focus knobs to bring the specimen into focus.
5. Increase magnification: Gradually increase the magnification by switching to higher-power objective lenses (e.g., 40x or 100x) and refocusing as needed.
6. Observe and record: Carefully observe the cells and chromosomes while adjusting the focus and lighting as necessary. Make observations and record your findings.

(ii) If the student cannot see the chromosomes clearly, they can improve visibility by using a higher-quality microscope, increasing the intensity of the microscope's light source, or using a more suitable stain. Additionally, adjusting the focus and ensuring the slide is properly prepared (e.g., reducing air bubbles) can help improve visibility of chromosomes during cell division.