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5.1.3Tools

Applying Techniques in Biology — IB Biology HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 4 of 10

📚 IB Biology HL Hub / Topical Revision
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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.
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Part 1 of 5Observing Structure

Light microscopy
  • Light microscopy Thin sections are placed on a slide, often stained,
    • and viewed at increasing magnification; focus with the coarse and then the fine adjustment.
Scale and magnification
  • Scale and magnification Magnification = image size ÷ actual size, and a scale bar lets the real size of a structure be found.
Graticule
  • Graticule An eyepiece graticule is calibrated against a stage micrometer at each objective lens before it is used for measuring cells.
Dissection
  • Dissection Organs are cut with a scalpel after pinning the specimen, and annotated drawings with a title, scale and labels record what is seen.
Electron microscopy
  • Electron microscopy Electron micrographs show ultrastructure at much higher resolution, but only dead, prepared specimens can be examined.

Part 2 of 5Separating and Analysing Molecules

Separating and Analysing Molecules
Chromatography
  • Chromatography Pigments or other molecules are carried by a solvent up a stationary phase, and each substance travels at a different speed.
Rf value
  • Rf value Rf = distance moved by the spot ÷ distance moved by the solvent front, which is always between 0 and 1.
Gel electrophoresis
  • Gel electrophoresis Charged molecules such as DNA fragments are separated by size as an electric current moves them through a gel.
Colorimetry
  • Colorimetry The absorbance of a coloured solution is measured and compared with standard solutions to find concentration.
Serial dilution
  • Serial dilution A solution is diluted step by step by the same factor, for example 1 : 10, to produce a range of concentrations.

Part 3 of 5Sampling and Culturing

Quadrats
  • Quadrats Frames placed at random positions estimate the number or percentage cover of plants or slow-moving animals in an area.
Transects
  • Transects A line across a habitat shows how species change along an environmental gradient such as a shore.
Mark-release-recapture
  • Mark-release-recapture Animals are caught, marked, released and recaptured,
    • so that population size can be estimated from the proportion of marked animals.
Aseptic culture
  • Aseptic culture Using sterile equipment and flame sterilisation helps microbes to be grown on agar without contamination.
TechniqueUsed to
ChromatographySeparate pigments
Gel electrophoresisSeparate DNA fragments by size
TransectStudy change along a gradient

Part 4 of 5Worked Example

Question

  • An image of a cell measures 45 mm across, and the actual cell is 0.15 mm across.
  • Calculate the magnification.
  • In a chromatogram a pigment moved 3.2 cm while the solvent front moved 8.0 cm.
  • Find its Rf value.

  1. Magnification = image size ÷ actual size = 45 ÷ 0.15 = 300, so ×300.
  2. Rf = distance moved by pigment ÷ distance moved by solvent front.
  3. Rf = 3.2 ÷ 8.0 = 0.40.

Answer The magnification is ×300 and the Rf value is 0.40 (no units).

Part 5 of 5Exam Checklist & Tips

5.1.3 – Key Points for the Exam

  • Magnification How many times larger an image is than the object.
  • Rf value Ratio of the distance moved by a substance to the distance moved by the solvent.
  • Quadrat A square frame used to sample organisms.
  • Stage micrometer A slide with a precise scale used to calibrate an eyepiece graticule.

Common Mistakes

  • Measuring the image and actual sizes in different units when calculating magnification.
  • Measuring the Rf distance from the top of the paper instead of from the starting line.
  • Placing quadrats where plants look most interesting instead of at random.
  • Forgetting to include a scale bar or magnification on a drawing.

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