Tools
5. Tools — IB Biology HL Revision Notes & Topical Questions
10 min read 12 parts Lesson 1 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.
Lesson summary
5. Tools — IB BIOLOGY HL notes: Apply safe practice, measuring techniques, technology, mathematics, uncertainty processing and graphing in biological investigations.Hazard = a feature of a procedure that may cause harm, such as an irritant chemical, slippery rocks on a shore or a…
- Risk assessment
- Safety precautions
- Volume of liquids
- Temperature
- Counting cells
- Counting organisms
Part 1 of 10Safety, ethical and environmental issues
Hazard
Hazard a feature of a procedure that may cause harm, such as an irritant chemical, slippery rocks on a shore or a Bunsen burner.
Risk
Risk the level of danger from a hazard, set by the likelihood of harm and its severity.
Risk assessment
- Risk assessment identify hazards, assess the level of risk and change the procedure to reduce it.
- A rocky shore quadrat study has slippery rocks as a hazard, with a likely fall causing bruises or twisted ankles.
- Control by requiring footwear with good grip, avoiding seaweed-covered rocks and walking slowly with care.
Chemicals
- Chemicals stains, enzyme-reaction reagents and chromatography solvents carry hazards shown by nine standardised hazard symbols in a red diamond.
| Symbol | Meaning |
|---|---|
| Health hazard | Skin rashes, eye damage or harm if swallowed |
| Corrosive | Skin burns and permanent eye damage |
| Flammable | Catches fire if heated or near a flame |
| Acute toxicity | Life-threatening effects even in small quantities |
| Hazardous to the environment | A threat to aquatic life and the environment |
| Oxidising | Can cause fire or explosions |
- Safety precautions
- name the hazard and justify the precaution, for example iodine is an irritant, so wear goggles and wash skin contact immediately.
Part 2 of 10Ethical and environmental considerations, measuring mass, volume and gases
Animals
- IB policy says to use animals only when there is no alternative, and without cruelty.
- Choose experiments without animals where possible.
- Minimise harm with short experiments, minimal handling and release at the end.
Humans
- Humans experiments such as using a spirometer need fully informed consent.
Laboratory environment
- Do not pour toxic chemical waste down the sink.
- Use a sharps bin for sharp equipment.
- Dispose of biological waste such as bacterial plates and dissected organs correctly.
Field environment
- Do not work in very large groups.
- Avoid sensitive environments.
- Take away equipment and litter.
Mass
- Mass a digital balance reading to two decimal places, tared (zeroed) before use so the container is excluded.
- 1 kg = 1000 g.
Volume of liquids
- Volume of liquids units are cm3, dm3, ml and litres, with 1 ml = 1 cm3.
- A measuring (graduated) cylinder gives approximate volumes in sizes from 10 cm3 to 1 dm3.
- A volumetric pipette is the most accurate for a fixed volume, usually 10 or 25 cm3, matching the bottom of the meniscus to the scratch mark.
- A burette is the most accurate for variable volumes from 0 to 50 cm3, read from the top because 0.00 is at the top.
Volume of gases
- A gas syringe is usually used.
- A graduated cylinder or burette inverted in water works if the gas is not water-soluble.
- An upright cylinder works for a coloured gas heavier than air.
Part 3 of 10Measuring time, temperature, length and counts, observation and techniques
Time
- Time a stopwatch or stop-clock, in seconds or minutes (1 min = 60 s).
- Human reaction time matters most for intervals under a second.
Temperature
- Temperature a thermometer or a digital probe (often 0.1 °C), in °C.
- (precision ½ or 1 °C)
Length
- Length a ruler reads to the nearest millimetre, and a tape measure covers larger distances.
- (1 cm = 10 mm and 100 cm = 1 m)
Counting cells
- Counting cells count in a known volume of culture to find concentration.
- A haemocytometer or counting chamber has a volumetric grid for counting particles and calculating concentration.
- A streak plate spreads a known volume of culture on growth medium, and direct counting is simple but slow.
Counting organisms
- Counting organisms accurate counts are rare because organisms move or are inconspicuous, so sampling is used.
- Errors come from population size, missed individuals, miscounting large groups and misidentification.
Annotated drawings
- Annotated drawings labelled line pictures of features observed under a microscope or in a micrograph, following drawing conventions.
Qualitative observations
- Qualitative observations classification by attributes such as sex, fur colour or number of limbs, which cannot be measured numerically.
Required techniques
- Required techniques describe the purpose and method of each.
- Paper or thin-layer chromatography.
- Colorimetry and serial dilutions.
- Physical and digital molecular modelling.
- Light microscope and eyepiece graticule.
- Preparation of temporary mounts.
- Identifying and classifying organisms.
- Random and systematic sampling.
- Karyotyping and karyograms.
- Cladogram analysis.
Part 4 of 10Technology to collect and process data
1
Collecting data
- Electronic sensors measure the abiotic environment and physiological factors such as lung volume and heart rate.
- Online databases (structured, searchable and sortable) give DNA sequence and chromosome data.
- Models and simulations predict real situations, such as population growth curves and mesocosm ecosystems.
2
Data loggers
Data loggers electronic devices that gather data quickly, store sensor readings over time and send them to a computer.
3
Sensors
Sensors input devices that detect changes and convert them into electrical signals stored in a data logger.
- A pH meter measures H+ concentration as a pH value, for example when testing pH and enzyme activity.
- A temperature probe replaces a thermometer when specific temperatures are needed.
4
Processing data
- Spreadsheets record, organise and calculate with data, including statistics, and build graphs and charts automatically.
- Computers handle data with large ranges, such as population data.
- Computers build models for ongoing predictions.
- Programs analyse images, such as joints in motion.
Part 5 of 10General mathematics
General mathematics
Calculation types
- Decimals, such as the size of a bacterial cell.
- Fractions, converted to decimals using the calculator button.
- Percentages, including percentage change and percentage difference.
- Ratios, most commonly surface area to volume.
- Proportions, as in scaling drawings of cells and tissues.
- Frequencies, such as allele frequency change.
- Densities, such as population density and stomatal density.
- Approximations, such as with the magnification formula.
- Reciprocals, such as 1/T in concentration-rate graphs.
Central tendency
- Mean = total of values divided by the number of values, a typical value.
- Median = the middle value when ordered, with 50% of values at or below it.
- Mode = the most frequent value, useful for categorical data.
Part 6 of 10Dispersion and scientific notation, rates, proportionality and percentages
1Standard deviation
Standard deviation the spread of data around the mean, and the mean must be found first.
2Standard error of the mean
Standard error of the mean how far the sample mean is likely to be from the true mean, always smaller than the SD.
3Interquartile range
Interquartile range the 75th percentile minus the 25th, with quartiles dividing the series into four equal parts.
4Scientific notation (standard form)
Scientific notation (standard form) a × 10n.
- a is between 1 and 10.
- n is a positive integer for large numbers and a negative integer for small numbers.
5
Approximation versus estimation
- Approximation finds a value close to the actual value when exact calculation is hard.
- Estimation is an educated assessment when the true value is unknown, such as the molecular clock dating of the first cells and LUCA.
6Magnification scales
- Magnification scales magnification is widely assessed.
Rate of change
Rate of change change in the dependent variable ÷ change in the independent variable, such as oxygen use in germinating seeds over days.
- Use the average rate from a table, or the gradient from a graph.
Direct proportionality
Direct proportionality a linear relationship in which doubling x doubles y.
Inverse proportionality
Inverse proportionality doubling x halves y.
Correlations
- Positive correlationthe gradient is positive and y rises with x.
- Negative correlationthe gradient is negative and y falls as x rises.
Percentage change
(final − initial) ÷ initial × 100.
Percentage difference
- Relative change(A − B) ÷ A × 100, using the baseline value as divisor.
- Symmetrical(A − B) ÷ ((A + B) ÷ 2) × 100, used when there is no baseline.
Part 7 of 10Data types and statistical tests
Data types and statistical tests
Discrete data
Discrete data quantitative, separate and countable, such as number of organisms.
Continuous data
Continuous data quantitative measurements that can take any value, such as temperature or volume of gas.
Test choice depends on sample size, type of data and the question.
| Test or index | Use |
|---|---|
| Simpson's reciprocal index | Measures relative biodiversity using richness and evenness; a higher value means greater biodiversity |
| Lincoln index | Estimates population size of an animal species |
| Chi-squared test | Compares observed and expected results |
| t-test | Tests whether the means of two data sets differ significantly (rough normal distribution, continuous data, similar standard deviations) |
| Correlation test | Tests the presence and strength of a correlation |
- Formulae are provided, and the task is to apply them.
Part 8 of 10SI units and significant figures
SI base units
- SI base units length metre (m), mass kilogram (kg), time second (s), temperature kelvin (K), amount of substance mole (mol), current ampere (A) and luminous intensity candela (cd).
Prefixes
- Prefixes kilo (k) 103, centi (c) 10−2, milli (m) 10−3, micro (µ) 10−6 and nano (n) 10−9.
| Quantity | Conversions |
|---|---|
| Length | 1000 m = 1 km; 0.01 m = 1 cm; 0.001 m = 1 mm; 10−6 m = 1 µm |
| Volume | 1 cm3 = 1 ml and 1 dm3 = 1 litre |
| Mass | 1000 kg = 1 tonne; 0.001 kg = 1 g |
| Time | 60 s = 1 min; 60 min = 1 hour |
| Pressure | 1000 Pa = 1 kPa |
| Energy | 1000 J = 1 kJ |
| Amount of substance | 0.001 mol = 1 millimole |
SI units and significant figures
"Amount" means moles, so refer to the mass, volume or concentration of a substance instead.
Significant figures
- All non-zero digits are significant.
- Zeros between non-zero digits are significant.
- Zeros before all non-zero digits are not significant.
- Zeros after non-zero digits in a number without a decimal point are not significant.
- Zeros after non-zero digits in a number with decimals are significant.
- To round, count to the required figure and look at the next digit: 5 or more rounds up.
Part 9 of 10Uncertainty and error bars
1Uncertainty
Uncertainty the range of values around a measurement within which the true value is expected to lie, written as ± to an appropriate precision.
- A balance with 10 g graduations has uncertainty ±5 g, and a pipette with 0.1 cm3 graduations ±0.05 cm3.
2
Error is the difference between a measured and true value, which is not the same as uncertainty.
3Error bars
- Error bars drawn above and below a point, usually vertical, to show uncertainty.
- (or side to side)
- They can show range, degree of precision, standard error or standard deviation, and the question states which.
- Overlapping standard deviation bars suggest two data sets are not significantly different.
4Precision
- Precision processed values and uncertainties must not exceed the precision of the original measurement, and raw data share one level of precision.
5Coefficient of determination (R2)
Coefficient of determination (R2) the fit of a trend line or curve to data.
- R2 = 0 means the dependent variable cannot be predicted.
- The closer R2 is to 1, the better the fit, and 1 is a perfect fit, though that does not guarantee a good model.
6Correlation coefficient (r)
Correlation coefficient (r) the strength of a linear relationship from −1 to +1, where ±1 is perfect and 0 means none.
7
Correlation does not mean causation.
8Hypotheses
- Hypotheses the null hypothesis says there is no significant difference or association, and the alternative says there is.
- Tests accept or reject the null hypothesis, and a non-significant result means differences are due to chance.
- A t-test compares means, a correlation test checks strength,
- and chi-squared tests observed against expected values,
- as in genetic crosses and species association.
Part 10 of 10Graphing
Graphing
Sketch graphs show qualitative trends, often proportional or inversely proportional.
Graph types
- Graph types bar chart, histogram, scatter graph, line or curve graph, logarithmic graph, pie chart and box-and-whisker plot.
Plotting rules
- Independent variable on the x-axis and dependent variable on the y-axis.
- Plot points accurately in pencil.
- Use linear scales that fit all data and fill the space.
- Label axes with units.
- Line graphs suit continuous data and bar charts suit grouped data.
Line of best fit
- Line of best fit it can be straight or curved and shows the trend.
- It need not pass through every point but must go through the majority, with points balanced on both sides.
- A curve must be smooth, and it passes through the origin only if the data allow it.
Tangent for initial rate
Extrapolate the curve back to time 0.
Draw a straight tangent touching the curve at that point, with a ruler and pencil and the curve fully visible.
Calculate the gradient
Calculate the gradient change in y ÷ change in x ('rise over run').
- For example, 72 cm3 in 20 s gives 3.6 cm3 s−1.
Graphing
Gradients
- Gradients non-linear graphs have changing gradients, which show how rate progresses and how factors such as concentration affect it.
Features of graphs
- Intercepts are where the line crosses an axis.
- Maxima are peaks where the gradient passes from positive through zero to negative,
- and minima are troughs where it passes from negative through zero to positive.
- Uncertainty bars show the absolute uncertainty of plotted values.
- Interpolation estimates values between points, and extrapolation extends the line beyond the data and is less reliable.
- The origin (0,0) is a good anchor if it is a true data point.
Biology-specific diagrams
- Biology-specific diagrams dichotomous keys, food chains, food webs, energy pyramids and pedigree charts.
Key terms
| Term | Meaning |
|---|---|
| Hazard | a feature of a procedure that can cause harm. |
| Risk | the likelihood and severity of harm from a hazard. |
| Data logger | a device that records sensor readings over time. |
| Tangent | a straight line touching a curve at one point, whose gradient gives the rate there. |
| Uncertainty | the range around a measurement within which the true value lies. |
| Coefficient of determination | R2, a measure of how well a line or curve fits data. |
| Standard deviation | a measure of the spread of data around the mean. |
Avoid these mistakes
1
Joining the points makes a line of best fit — the line shows the trend through most points and may be straight or curved.
2
Wearing goggles is enough for a safety plan — the hazard must be named and the precaution justified.
3
Uncertainty and error are the same — uncertainty is a range around a measurement, and error is the difference from the true value.
4
Burettes are read from the bottom — zero is at the top.
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