5.1.3Tools
Applying Techniques in Biology — IB Biology SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 4 of 10
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.
Part 1 of 6Separating and Measuring
Chromatography
- Chromatography Mixtures separate on paper or a thin layer as a solvent moves up;
- each substance travels a different distance depending on solubility and attraction to the paper.
Rf value
- Rf value Rf equals the distance moved by the substance divided by the distance moved by the solvent front;
- it is always less than 1.
Colorimetry
- Colorimetry A colorimeter measures absorbance of light by a coloured solution, which relates to its concentration.
Serial dilution
- Serial dilution Repeatedly diluting a solution by a fixed factor, such as 1 in 10, gives a range of known concentrations.
Part 2 of 6Microscopy and Observation
1
Make a temporary mount by placing a thin specimen in a drop of water or stain on a slide and lowering a coverslip at an angle.
2
Start with the lowest-power objective, and focus using the coarse then the fine adjustment.
3
Calibrate the eyepiece graticule against a stage micrometer for each objective lens.
4
Draw what is seen with clear continuous lines, no shading, and label the structures.
5
Calculate magnification from the size of the drawing divided by the actual size.
Part 3 of 6Sampling Ecosystems
Sampling Ecosystems
Random sampling
- Random sampling Quadrats are placed at coordinates chosen by random numbers, which avoids bias when an area is uniform.
Systematic sampling
- Systematic sampling Samples are taken at regular intervals along a transect, which suits a gradient such as moving away from the shore.
Identification
- Identification Dichotomous keys classify organisms using clear observable features.
Reliability
- Reliability More samples reduce the effect of chance on estimates of abundance.
Part 4 of 6Genetic and Evolutionary Tools
Karyotyping
- Karyotyping Chromosomes from a dividing cell are photographed and arranged in pairs by size and banding to show the full chromosome set.
Uses of karyograms
- Uses of karyograms They can reveal chromosome number errors such as Down syndrome, and show the sex of an individual.
Cladograms
- Cladograms Branching diagrams show evolutionary relationships based on shared derived characteristics or DNA sequences.
Molecular models
- Molecular models Physical or digital models show the shapes of molecules such as proteins and DNA.
Part 5 of 6Worked Example
Question
- In a chromatography experiment the solvent front moved 8.0 cm and a pigment spot moved 3.6 cm from the origin.
- Calculate the Rf value.
- Rf = distance moved by pigment ÷ distance moved by solvent front.
- Rf = 3.6 ÷ 8.0.
- The distances use the same unit, so Rf has no unit.
Answer Rf = 0.45.
Part 6 of 6Exam Checklist & Tips
5.1.3 – Key Points for the Exam
- Chromatography A technique for separating the components of a mixture.
- Rf value Distance moved by a substance divided by the distance moved by the solvent front.
- Serial dilution A stepwise dilution by a constant factor.
- Karyogram An image of the chromosomes of a cell arranged in pairs.
- Cladogram A tree diagram showing evolutionary relationships.
Common Mistakes
- Drawing the origin line in ink or below the solvent level, so that pigments dissolve into the solvent.
- Giving an Rf value greater than 1.
- Using only the high-power lens to find a specimen.
- Shading or sketching with overlapping lines in a biological drawing.
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