Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

1.3.2Additional lessons

Cell Theory- Skills — IB Biology SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 1 of 142

📚 IB Biology SL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
0%read

Part 1 of 6Parts of the Light Microscope

Eyepiece lens
  • Eyepiece lens The lens you look through, which usually magnifies the image ten times.
Objective lenses
  • Objective lenses A set of lenses of different power on a turret;
    • rotating the turret changes the total magnification.
Stage
  • Stage The flat platform that holds the slide, with clips to keep it still while it is being viewed.
Light source
  • Light source A lamp below the stage that shines light up through the thin specimen into the objective lens.
Focus knobs
  • Focus knobs The coarse knob brings the image roughly into focus and the fine knob sharpens it, mainly at higher power.

Part 2 of 6Making a Temporary Mount

1
For a liquid specimen, place a few drops on the slide with a pipette; for a solid, cut a very thin layer of tissue.
2
Add a drop of a suitable stain if the structures are colourless, because stains make parts of the cell easier to see.
3
Lower a coverslip gently at an angle onto the specimen so that air bubbles are not trapped beneath it.
4
Wear gloves, because stains can mark skin, and take care with scalpels and other sharp tools.
5
Place the slide on the stage and secure it with the clips before switching on the lamp.

Part 3 of 6Focusing Safely

1
Always begin with the lowest power objective lens, since the field of view is larger and the specimen is easier to find.
2
Turn the coarse focus until the specimen comes into view, then use the fine focus to sharpen details.
3
Centre the part you want to study, then rotate the turret to the next objective lens without moving the stage down.
4
At higher power use only the fine focus, to avoid pushing the lens into the coverslip.
5
If the image is blurred, return to low power and check that the specimen is thin enough for light to pass through.

Part 4 of 6Measuring with a Graticule

Measuring with a Graticule
Graticule
  • Graticule A small disc with an engraved scale placed in the eyepiece, which has no fixed units of its own.
Stage micrometer
  • Stage micrometer A slide with a scale of known length, used to find what one graticule division is worth.
Calibration
  • Calibration The graticule is lined up with the stage micrometer separately for each objective lens, because the value changes.
Measurement
  • Measurement Count how many graticule divisions the cell covers and multiply by the calibrated value of one division.

Part 5 of 6Worked Example

Question

  • Forty graticule divisions lie exactly alongside 0.20 mm of a stage micrometer.
  • A cell covers 12 graticule divisions.
  • Find the cell length, and the magnification if its drawing is 45 mm long.

  1. Convert 0.20 mm to micrometres: 0.20 × 1000 = 200 µm.
  2. Value of one division = 200 µm ÷ 40 = 5 µm.
  3. Cell length = 12 × 5 µm = 60 µm.
  4. Convert drawing length45 mm × 1000 = 45 000 µm.
  5. Magnification = image size ÷ actual size = 45 000 ÷ 60 = 750.

Answer The cell is 60 µm long and the drawing has a magnification of ×750.

Part 6 of 6Exam Checklist & Tips

1.3.2 – Key Points for the Exam

  • Magnification How many times larger an image is than the real object.
  • Graticule An eyepiece scale used as a ruler in the field of view.
  • Stage micrometer A slide carrying a scale of known size used to calibrate a graticule.
  • Temporary mount A slide of fresh specimen under a coverslip that is prepared for immediate viewing.
  • Field of view The area of the specimen that can be seen through the microscope at one time.

Common Mistakes

  • Starting on the high power lens; always start on low power to find the specimen and protect the lens.
  • Using the same graticule value for every objective lens; it must be recalibrated each time the lens changes.
  • Dropping the coverslip flat so that air bubbles are trapped and look like cells.
  • Using the coarse focus at high power, which can crack the coverslip or damage the lens.

Last updated:

Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.

\n