Welcome to Data Handling, Graphs, and Calculations!

In Human Biology, we don’t just look at pictures of cells or organs; we also use numbers to understand how the body works. Whether you are calculating a patient's Body Mass Index (BMI) or analyzing the results of an enzyme experiment, being "good with data" is a superpower that helps you see patterns others might miss. This guide will break down the essential math and graphing skills you need for your Edexcel IGCSE exams.

1. Mastering the Numbers: Essential Math Skills

You don’t need to be a mathematician, but you do need to be comfortable with a few basic tools. These skills appear in almost every exam paper!

Averages: Mean, Median, and Mode

When we repeat an experiment (like measuring pulse rate), we often get slightly different results. Averages help us find a representative value.

  • Arithmetic Mean: Add all the numbers together and divide by how many numbers there are.
    Example: Pulse rates of \(70\), \(72\), and \(74\).
    \( \text{Mean} = \frac{70 + 72 + 74}{3} = 72 \text{ beats per minute} \)
  • Median: The middle value when the numbers are listed in order.
  • Mode: The number that appears most often in a data set.

Percentages and Ratios

Biology often involves comparing sizes or amounts.

  • Percentage Change: This shows how much something increased or decreased.
    \( \text{Percentage Change} = \frac{\text{Change}}{\text{Original Value}} \times 100 \)
  • Ratios: These compare two quantities. If there are \(10\) red blood cells for every \(1\) white blood cell, the ratio is \(10:1\). Always simplify ratios if possible (like simplifying fractions!).

Standard Form and Significant Figures

Some biological numbers are tiny (like the width of a DNA molecule) or huge (like the number of cells in the body).

  • Standard Form: Written as \(A \times 10^n\). For example, \(0.005\) becomes \(5 \times 10^{-3}\).
  • Significant Figures (sig figs): This is about rounding to show how precise your measurement is. If the question asks for \(3\) sig figs, \(123.45\) becomes \(123\).
Quick Review: The Calculator Rule

You are expected to have a calculator for all papers. However, make sure yours does not have a QWERTY keyboard or the ability to store text, as these are not allowed in the exam!

2. The "Must-Know" Biology Formulas

While some formulas are provided, you are expected to memorize and apply these specific ones for the Human Biology syllabus:

Body Mass Index (BMI)

Used to assess if a person is a healthy weight for their height.

\( \text{BMI} = \frac{\text{mass in kg}}{(\text{height in m})^2} \)

Common Mistake: Don't forget to square the height! If someone is \(2\text{m}\) tall, you divide the mass by \(4\) (which is \(2 \times 2\)).

Aerobic Respiration

You must know both the word and the balanced chemical symbol equation:

Word: \( \text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water} \ (+ \text{energy}) \)

Symbol: \( \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} \)

Anaerobic Respiration

For humans (in muscles), you only need the word equation:

Word: \( \text{glucose} \rightarrow \text{lactic acid} \ (+ \text{energy}) \)

3. Graphing: Turning Numbers into Pictures

If a question asks you to Plot, Sketch, or Draw, follow these golden rules to avoid losing "easy" marks.

Choosing the Right Graph

  • Bar Charts: Use these when one variable is discrete (categories like "Blood Group A, B, AB, O").
  • Histograms: Use these for continuous data that has been grouped into ranges (e.g., "Number of people with heights between \(150\text{--}160\text{cm}\)").
  • Scatter Diagrams: Use these to look for a trend or correlation between two variables (e.g., "Age vs. Blood Pressure").

The SLAPUK Checklist for Plotting

When you are asked to Plot a graph, check your work against these letters:

  • S (Scale): Does the graph fill at least half of the provided grid? Use sensible intervals (e.g., \(2\text{s}, 5\text{s}, 10\text{s}\)).
  • L (Line): Draw a Line of Best Fit. This can be a straight line or a smooth curve. It should follow the trend and ignore anomalous (weird) results.
  • A (Axes): The Independent Variable (the one you change) goes on the \(x\)-axis (bottom). The Dependent Variable (the one you measure) goes on the \(y\)-axis (side).
  • P (Points): Plot your points accurately using a small \(x\) or a dot with a circle around it.
  • U (Units): Always include units in your axis labels (e.g., \( \text{Time / seconds} \)).
  • K (Key): If you are plotting two different sets of data on the same graph, use a key to show which is which.
Did you know?

A Line of Best Fit does not have to go through every single point. Its job is to show the overall pattern. If one point is far away from all the others, it might be an "anomaly"—a mistake in the experiment!

The exam will often ask you to Describe or Explain a graph. These mean two different things!

  • Describe: Say what you see. (e.g., "As temperature increases, the rate of enzyme activity increases until \(40^\circ\text{C}\), then it decreases.")
  • Explain: Say why it is happening using your biology knowledge. (e.g., "The rate decreases after \(40^\circ\text{C}\) because the enzymes have denatured.")
  • Determine: This usually means you need to find a specific value from the graph. For example, "Determine the heart rate at \(5\) minutes" means you find \(5\) on the \(x\)-axis, go up to the line, and read the value on the \(y\)-axis.

Slope and Intercept

For a linear (straight-line) graph, the slope (gradient) tells you the rate of change. A steeper slope means a faster change. The intercept is where the line crosses the axis.

5. Exam Command Words: A Quick Guide

Pay close attention to these words in the "Practical and Mathematical Skills" section:

  • Calculate: Use numbers from the question to find an answer. Show your working! Even if your final answer is wrong, you can get marks for the steps.
  • Estimate: Give an approximate value. You can often do this by rounding numbers to make them easier to handle in your head.
  • Predict: State what you think will happen in the future based on the data you have.
  • Show that: The answer is already given; you must provide the mathematical steps to reach it.

Note: For more information on how to design the experiments that produce this data, see the chapter on "Experimental design, variables and evaluation."

Key Takeaways Summary

1. Practice your BMI: Remember \( \text{mass} / \text{height}^2 \).
2. Graphing Precision: Always label axes with units and use at least half the page.
3. Read carefully: Check if the question asks for "Mean" (average) or "Range" (smallest to largest).
4. Symbols matter: Be ready to write out the balanced symbol equation for aerobic respiration.