6.1Unit 6: Practical Skills in Biology II
Practical Skills in Biology II — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 8 parts Lesson 1 of 48 2 quizzes
Lesson summary
6.1 Practical Skills in Biology II — IAL EDEXCEL LINEAR notes: Plan, record, present and evaluate investigations, using variables, controls, tables, graphs and error analysis.Hypothesis = a testable prediction.Independent variable = the factor you change.Dependent variable = the …
- Control variables
- Planning sequence
- Risk assessment
- Statistical tests
- Random error
- Systematic error
Section 1 of 8Planning: hypothesis and variables
1Hypothesis
Hypothesis a testable prediction.
2Independent variable
Independent variable the factor you change.
3Dependent variable
Dependent variable the factor you measure.
4Control variables
- Control variables at least three are named and kept the same, because 'everything else constant' is not specific enough.
5Planning sequence
- Planning sequence state a hypothesis, identify variables and controls, then plan a method with repeats.
Section 2 of 8Recording results
Tables
- Tables headings carry the units, not each number.
Precision
- Precision all readings use the number of decimal places the instrument allows, with suitable significant figures.
Repeats
- Repeats repeat readings and calculate a mean.
Anomalies
- Anomalies identify them, discard them only with a reason, and explain them.
Risk assessment
- Risk assessment one is required for every practical.
Section 3 of 8Presenting data in graphs
Axes
- Axes the independent variable goes on the x axis, and both axes are labelled with quantity and unit.
Scale
- Scale choose a scale that uses at least half of the grid.
Line
- Line draw a line of best fit, not dot to dot, and do not force it through the origin unless the data support it.
Statistical tests
- Statistical tests a t-test, chi-squared test or Spearman's rank test is chosen to match the data.
Section 4 of 8Evaluating the investigation
Evaluating the investigation
Random error
Random error readings scatter either side of the true value, and it is reduced by repeating.
Systematic error
Systematic error every reading is shifted the same way, so repeating does not help; the instrument must be zeroed or the method changed.
Precision
Precision repeats agree with each other.
Accuracy
Accuracy results are close to the true value, and readings can be precise and still wrong.
Repeatability
Repeatability the same results when repeated by the same person.
Reproducibility
Reproducibility the same results when other people or other methods are used.
Improvements
- Improvements they must be specific, for example using a water bath to hold the temperature at 30 °C instead of 'being more accurate'.
Serial dilution
Serial dilution a stepwise dilution of a solution, used to make standards for calibration curves.
Section 5 of 8More from the specification
1
Photosynthesis rate
- The rate can be measured by counting oxygen bubbles or collecting gas volume from pondweed such as Elodea at different light intensities, with temperature and carbon dioxide controlled.
2
Pigments
- Chlorophyll a, chlorophyll b and carotenoids in the thylakoid membranes absorb light energy;
- each pigment absorbs different wavelengths, shown by chromatography.
3
Light-dependent reactions
- Photosystem II uses light to excite electrons which pass along an electron transport chain, generating ATP and reduced NADP while water is split to release oxygen.
4
Calvin cycle
- Carbon dioxide is fixed by RuBisCO onto RuBP and the products are reduced to triose phosphate using ATP and reduced NADP.
5
Limiting factors
- Light, carbon dioxide concentration and temperature can each limit the rate of the plant reactions.
6
Photosynthesis rate
- The rate can be measured by counting oxygen bubbles or collecting gas volume from pondweed such as Elodea at different light intensities, with temperature and carbon dioxide controlled.
7
Pigments
- Chlorophyll a, chlorophyll b and carotenoids in the thylakoid membranes absorb light energy;
- each pigment absorbs different wavelengths, shown by chromatography.
8
Light-dependent reactions
- Photosystem II uses light to excite electrons which pass along an electron transport chain, generating ATP and reduced NADP while water is split to release oxygen.
9
Calvin cycle
- Carbon dioxide is fixed by RuBisCO onto RuBP and the products are reduced to triose phosphate using ATP and reduced NADP.
10
Limiting factors
- Light, carbon dioxide concentration and temperature can each limit the rate of the plant reactions.
11
Solvent
- The liquid that a solute dissolves in.
12
Chloroplast
- Organelle where photosynthesis takes place.
13
Chromatography
- A technique to separate substances in a mixture.
14
Absorption
- Movement of digested molecules into the blood or lymph.
15
Photophosphorylation
- Production of ATP using light energy.
16
Light intensity
- The amount of light reaching a plant.
17
Limiting factor
- A factor in shortest supply that restricts a rate.
18
Molecule
- Two or more atoms bonded together.
19
Electron
- Negative particle with almost no mass that moves around the nucleus.
20
Hydrogen
- A flammable gas that burns with a squeaky pop.
Section 6 of 8Key terms
| Term | Meaning |
|---|---|
| Hypothesis | A testable prediction. |
| Independent variable | The factor you change. |
| Dependent variable | The factor you measure. |
| Control variable | A factor kept constant. |
| Repeatability | Same results when repeated by the same person. |
| Reproducibility | Same results when repeated by others or with other methods. |
| Serial dilution | Stepwise dilution of a solution. |
| Systematic error | An error that shifts every reading in the same direction. |
Section 7 of 8Syllabus checklist
| Practical | Variable changed | Measurement | Key control |
|---|---|---|---|
| Photosynthesis rate (Elodea) | Light distance, CO2 or temperature | Volume of oxygen per minute | Temperature, using a glass tank to absorb lamp heat |
| Quadrat and transect | Position along a gradient | Abundance or percentage cover | Random co-ordinates, same quadrat size |
| Temperature and development | Temperature | Seedling growth or hatching rate | Light, moisture, water volume |
| Yeast growth | Temperature or glucose | Colorimeter absorbance (turbidity) | Sterile technique, same inoculum |
| Antibiotics | Antibiotic type or concentration | Clear zone diameter or area | Disc size, plate lawn, incubation time |
| Respiration in yeast | Temperature or substrate | Time for DCPIP or methylene blue to decolourise | Volumes of yeast and dye |
| Respirometer RQ | Substrate or temperature | Oxygen uptake and RQ | Temperature, organism mass, soda lime |
| Exercise and breathing | Exercise | Spirometer trace | Same subject, rest and recovery times |
| Gibberellin and amylase | Gibberellin concentration | Clear zone on starch agar | Grain half size, soaking time |
Section 8 of 8Exam technique
1
Writing 'keep everything else constant' — name each control variable.
2
Putting units beside every value in a table — units go in the column heading.
3
Joining graph points dot to dot — draw a line of best fit.
4
Confusing precision with accuracy — precise results agree with each other and accurate results are close to the true value.
Marked practiceQuizzes for this lesson
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