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Microscope and Mitosis Lab Notes

The Light Microscope

  • A light microscope uses a beam of light and a combination of lenses to magnify an object that is too small to see with the unaided eye.

  • The most-used device in this lab is the compound light microscope.

    • The term compound refers to the two sets of lenses used.

    • Ocular lenses are located within the eyepieces.

    • Objective lenses are suspended above the stage and offer various powers of magnification.

Anatomy of the Compound Light Microscope

  • Key components (as shown in Figure 3.2):

    • Arm

    • Head

    • Ocular lenses / Eyepieces

    • Revolving nosepiece

    • Objective lenses

    • Stage clip (slide holder)

    • Condenser knob (regulates height of condenser)

    • Coarse adjustment knob

    • Stage

    • Condenser

    • Iris diaphragm control

    • Mechanical stage control knobs

    • Fine adjustment knob

    • Light control

    • Substage illuminator

    • Base

Basic Handling and Safety

  • Never carry a microscope with one hand. Always hold the base and the arm.

  • Do not touch the lenses unless you have lens cleaning paper.

  • Plug in the microscope for the light source and switch it off promptly when you are done.

  • Always place the microscope on a clean table. Do not place it on a notebook or laptop.

  • Breakages and damages need to be paid for by the responsible student. Exercise caution.

Important Terms and Concepts

  • Resolution

    • The ability of a microscope to show details of the specimen.

    • Minimum distance at which two distinct points on a specimen can be seen clearly.

  • Total magnification

    • Power of the ocular lens × Power of the objective lens used.

    • ext{Total Magnification} = ( ext{Ocular Power}) imes ( ext{Objective Power})

  • Field of view

    • Area of the slide visible through the microscope when you look into the eyepieces.

  • Working distance

    • Distance between the slide/specimen and the tip of the objective lens.

    • When you increase magnification, the working distance decreases.

Activity 1: Total Magnification Table (Table 3.3)

  • Objective powers and corresponding totals (typical values; results may vary if lens powers differ):

    • Scanning: Objective Power 4x, Ocular Power 10x, Total Magnification 40\times

    • Low: Objective Power 10x, Ocular Power 10x, Total Magnification 100\times

    • High: Objective Power 40x, Ocular Power 10x, Total Magnification 400\times

    • Oil immersion: Objective Power 100x, Ocular Power 10x, Total Magnification 1000x

Activity 2

  • Follow the instructions in the lab printout for Procedure 3 and record your results.

  • Use one slide per group as provided by your instructor.

Activity 3

  • Take a picture of the mitosis model presented in the lab and add it to your lab notebook binder.

Phases of Mitosis

  • Cell Division: Mitosis followed by Cytokinesis.

  • The stages of cell division oversee the separation of identical genetic material into two new nuclei, followed by the division of the cytoplasm.

  • Prophase:

    • Chromosomes condense and become visible

    • Spindle fibers emerge from the centrosomes

    • Nuclear envelope breaks down

    • Centrosomes move toward opposite poles

  • Prometaphase:

    • Chromosomes continue to condense

    • Kinetochores appear at the centromeres

    • Mitotic spindle microtubules attach to kinetochores

  • Metaphase:

    • Chromosomes are lined up at the metaphase plate

    • each sister chromatid is attached to a spindle fiber originating from opposite poles

  • Anaphase:

    • Centromeres split in two

    • sister chromatids (now called chromosomes) are pulled towards opposite poles

    • certain spindle fibers begin to elongate the cell

  • Telophase:

    • Chromosomes arrive at opposite poles and begin to decondence

    • nuclear envelope material surrounds each set of chromosomes

    • the mitotic spindle breaks down

    • spindle fibers continue to push poles apart

  • Cytokinesis:

    • Animal cells: a cleavage furrow separates the daughter cells

    • Plant cells: a cell plate, the precursor to a new cell wall, separates the daughter cells

Answers to Lab Activities (Lab Activity 3A)

  • Table 3.3 (example values; results may vary with different lenses):

    • Scanning: Objective Power 4x, Ocular Power 10x, Total Magnification 40\times

    • Low: Object Power 10x, Ocular Power 10x, Total Magnification 100\times

    • High: Object Power 40x, Ocular Power 10x, Total Magnification 400\times

    • Oil immersion: Object Power 100x, Ocular Power 10x, Total Magnification 1000\times

  • Observations (a–c):

    • (a) The "e" is bigger than the field of view at high power (400×). You have zoomed in so closely that the entire letter no longer fits in the field of view.

    • (b) The field of view gets smaller/decreases in size.

    • (c) The working distance gets smaller as the magnification increases.

Topics to Review for the Lab Exam

  • Table 3.2 – Parts of a compound microscope

  • Mitosis model

Practical and Conceptual Implications

  • Understanding how magnification, resolution, field of view, and working distance relate helps in planning observations and choosing appropriate objectives for different specimens.

  • Safety and proper handling are essential to prevent damage to equipment and ensure accuracy of observations.

  • The mitosis model connects structure to function, illustrating how genetic material is separated into two nuclei and how cytoplasmic division follows.

Quick Reference (Key Terms and Formulas)

  • Total Magnification: ext{Total Magnification} = ( ext{Ocular Power}) imes ( ext{Objective Power})

  • Common magnifications:

    • Scanning objective: 4x; Ocular: 10x; Total: 40\times

    • Low objective: 10x; Ocular: 10x; Total: 100\times

    • High objective: 40x; Ocular: 10x; Total: 400\times

    • Oil immersion: 100x; Ocular: 10x; Total: 1000\times

  • Important relationships:

    • As magnification increases, field of view decreases and working distance decreases.