Class 12 Biology PBA: Setup and Observation of Light Microscope | FBISE Federal Board

Microscopy Study Guide: Detailed Setup & Observation

According to [SLO: B-11-X-02 (ix)], students must be able to set up a light microscope to view and observe specimens. Below is the summarized process for achieving a clear and focused image.

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1. Preparation and Light Alignment

• Stability: Place the microscope on a flat, level surface to prevent vibration.
• Illumination: Adjust the mirror or turn on the built-in light source. Ensure the light passes through the diaphragm and condenser to provide a bright, uniform field of view.

2. Mounting the Specimen

• Slide Placement: Place the slide on the stage, centering the specimen over the hole where light passes through.
• Securing: Use the stage clips to hold the slide firmly in place to prevent it from moving during observation.

3. The Focusing Sequence

To avoid damaging the slide or the lens, always follow this numbered sequence:

1. Start Low: Rotate the revolving nosepiece to the lowest power objective lens (usually 4x or 10x). This provides the widest field of view.
2. Coarse Adjustment: While looking from the side (not through the eyepiece), use the coarse adjustment knob to bring the objective lens as close to the slide as possible without touching it.
3. Viewing: Look through the eyepiece (ocular lens) and slowly turn the coarse adjustment knob in the opposite direction until the specimen comes into view.
4. Fine Adjustment: Use the fine adjustment knob to sharpen the image and see the internal structures of the specimen clearly.

4. Increasing Magnification

• Once the specimen is focused under low power, rotate the nosepiece to a higher power objective lens.
• Caution: When using high power, only use the fine adjustment knob to avoid cracking the slide, as the lens is very close to the specimen.

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Summary Table for Students

Action	Component Used
Initial Focus	Coarse Adjustment Knob
Detail Sharpening	Fine Adjustment Knob
Changing Zoom	Revolving Nosepiece
Light Control	Diaphragm / Iris

FBISE Study Guide: Microscopy (SLO: B-11-X-02)

This guide covers the essential technical skills required to set up, focus, and observe specimens using a light microscope.

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1. Essential Components & Setup

Before observation begins, the microscope must be properly configured on a stable surface to ensure image clarity and equipment safety.

• Stability: Place the instrument on a flat, level surface to avoid vibrations.
• Illumination: Adjust the light source or mirror to reflect light through the diaphragm.
• Mounting: Place the slide on the stage and fix it with stage clips.

2. Standard Operating Procedure (Focusing)

1. Low Power First: Always start with the lowest power objective lens.
2. Coarse Focus: Use the coarse adjustment knob to bring the specimen into view.
3. Fine Focus: Use the fine adjustment knob to sharpen the details.
4. Magnification: Rotate the revolving nosepiece to a higher power objective if needed.

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Section I: Short Questions

1. What is the first step in focusing a specimen?

Select the lowest power objective lens and use the coarse adjustment knob.

2. Why is the fine adjustment knob used?

To sharpen the image and observe small, detailed structures within the specimen.

3. What holds the slide in place?

The stage clips located on the microscope stage.

4. How is magnification changed?

By rotating the revolving nosepiece to select a different objective lens.

5. Why use a flat surface for microscopy?

To prevent the microscope from tilting and to ensure the optical path remains stable.

6. When should you avoid the coarse adjustment knob?

When using high-power objective lenses, to prevent breaking the slide.

7. What is the role of the light source?

To illuminate the specimen so it can be seen through the ocular lens.

8. Define the purpose of SLO B-11-X-02 (ix).

To master the setup and observation techniques for light microscopy.

9. How do you center a specimen?

By moving the slide on the stage until the specimen is directly over the light hole.

10. What is the final step of observation?

Using the fine adjustment knob under high power for maximum detail.

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Section II: Multiple Choice Questions (MCQs)

No.	Question	Correct Answer
1	Which lens is used first for observation?	Lowest power objective
2	Which knob is used for rapid focusing?	Coarse adjustment
3	Where is the slide placed?	Stage
4	What part rotates the lenses?	Revolving nosepiece
5	Which knob is safe for high power?	Fine adjustment
6	What provides the light?	Mirror or Lamp
7	What secures the slide?	Stage clips
8	To see more detail, you should:	Increase magnification
9	If the image is blurry, adjust the:	Fine adjustment knob
10	Microscopy requires a surface that is:	Flat and stable