Human Gas Exchange » Breathing Investigation Practical

What you'll learn this session

Study time: 30 minutes

How to design and conduct a breathing rate investigation
The relationship between exercise and breathing rate
How to measure and record breathing rate accurately
Variables affecting breathing rate
How to analyse and interpret breathing investigation data
How to draw valid conclusions from experimental results

Introduction to Breathing Investigation Practical

Our bodies need a constant supply of oxygen for cellular respiration and must remove carbon dioxide efficiently. During exercise, our muscles work harder and require more oxygen, leading to changes in our breathing rate. In this practical investigation, we'll explore how exercise affects our breathing rate and why these changes occur.

Key Definitions:

Breathing rate: The number of breaths taken per minute.
Ventilation: The process of moving air into and out of the lungs.
Tidal volume: The amount of air moved in or out of the lungs during normal breathing.
Independent variable: The factor you change in an experiment (exercise intensity).
Dependent variable: The factor you measure in an experiment (breathing rate).

💪 Why Exercise Affects Breathing

When we exercise, our muscles need more energy. This means they need more oxygen for aerobic respiration and produce more carbon dioxide as waste. To meet this demand, our breathing rate increases to take in more oxygen and remove more carbon dioxide. This is why you breathe faster when you run or do other physical activities!

🧠 Scientific Question

For our investigation, we'll ask: "How does exercise intensity affect breathing rate?" This question is specific, measurable and allows us to design a fair test. We can predict that as exercise intensity increases, breathing rate will also increase to supply more oxygen to working muscles.

Planning Your Investigation

A good investigation needs careful planning to ensure reliable results. Let's look at how to set up our breathing rate experiment.

Variables in Our Investigation

To make our experiment fair and reliable, we need to identify and control our variables:

📝 Independent Variable

Exercise intensity (e.g., rest, walking, jogging, running)

📊 Dependent Variable

Breathing rate (breaths per minute)

🛠 Control Variables

Age, fitness level, time of day, recovery time between exercises, room temperature

Equipment Needed

Stopwatch or timer
Recording sheet
Step or bench (for step exercise)
Calculator
Graph paper or computer with graphing software

Method for Breathing Rate Investigation

Follow these steps to conduct your investigation safely and accurately:

Measure resting breathing rate: Count the number of breaths (one inhalation + one exhalation = one breath) for 1 minute while sitting quietly. Record this as your resting breathing rate.
Perform light exercise: Walk at a normal pace for 2 minutes.
Measure breathing rate immediately: Count breaths for 1 minute and record.
Rest period: Sit quietly for 5 minutes to allow your breathing to return to normal.
Perform moderate exercise: Jog on the spot for 2 minutes.
Measure breathing rate again: Count breaths for 1 minute and record.
Rest period: Sit quietly for 5 minutes.
Perform vigorous exercise: Do step-ups (stepping up and down on a bench) for 2 minutes.
Measure breathing rate again: Count breaths for 1 minute and record.
Repeat the entire procedure twice more: This gives you three trials for each exercise intensity.

Safety First! ⚠

When conducting exercise investigations:

Make sure participants are healthy and fit enough for exercise
Stop immediately if anyone feels dizzy, faint, or experiences chest pain
Allow adequate rest between exercise periods
Have water available for participants
Exercise on a non-slip surface

Recording Your Results

Create a table like this to record your results:

Exercise Intensity	Trial 1 (breaths/min)	Trial 2 (breaths/min)	Trial 3 (breaths/min)	Mean (breaths/min)
Rest
Walking
Jogging
Step-ups

Analysing Your Results

After collecting your data, you need to analyse it to draw conclusions:

📈 Calculating Mean Values

For each exercise intensity, calculate the mean (average) breathing rate using this formula:

Mean = (Trial 1 + Trial 2 + Trial 3) ÷ 3

For example, if your breathing rates after jogging were 24, 26 and 25 breaths per minute:

Mean = (24 + 26 + 25) ÷ 3 = 75 ÷ 3 = 25 breaths per minute

📊 Creating a Graph

Draw a line graph to show your results:

X-axis: Exercise intensity (rest, walking, jogging, step-ups)
Y-axis: Mean breathing rate (breaths per minute)
Plot your mean values and connect the points with a line
Add a title, label both axes and include units

Interpreting Your Results

Look at your graph and consider these questions:

How does breathing rate change with increasing exercise intensity?
Is there a pattern or relationship between the variables?
Does your data support your prediction?
Are there any unusual results (outliers) that don't fit the pattern?

Explaining Your Results

When you exercise, your muscles need more energy from respiration. This increases your body's demand for oxygen and produces more carbon dioxide. Your breathing rate increases to:

Bring more oxygen into the lungs for diffusion into the bloodstream
Remove more carbon dioxide from the body
Maintain homeostasis (balance) in the body

The increase in breathing rate is detected and controlled by:

Chemoreceptors in the carotid arteries and aorta that detect changes in blood CO₂ levels
The respiratory centre in the medulla oblongata (part of the brain stem)
The intercostal muscles and diaphragm, which respond by contracting more frequently

Case Study Focus: Athletes and Breathing Efficiency

Elite athletes often have lower resting breathing rates than non-athletes. For example, Olympic swimmers might have resting rates of 10-12 breaths per minute compared to the average 12-20 breaths per minute. Through training, athletes develop:

Larger lung capacity
More efficient oxygen extraction
Greater tidal volume (amount of air per breath)
Stronger respiratory muscles

This means they can take fewer, deeper breaths while still meeting their oxygen needs, even during intense exercise.

Evaluating Your Investigation

Every scientific investigation has strengths and limitations. Consider:

✅ Strengths

Simple equipment needed
Easy to repeat multiple times
Clear relationship between variables
Multiple trials improve reliability

❌ Limitations

Counting breaths manually may introduce error
Exercise intensity is difficult to standardise
Individual differences (fitness, age, gender) affect results
Environmental factors (temperature, humidity) may influence breathing

Improvements and Extensions

How could you improve or extend this investigation?

Use a spirometer to measure breathing volume as well as rate
Monitor recovery time - how long until breathing returns to normal?
Compare breathing rates between different age groups or fitness levels
Use a heart rate monitor to correlate heart rate with breathing rate
Investigate the effect of different types of exercise (aerobic vs anaerobic)

Summary

In this practical investigation, we've explored how exercise affects breathing rate. We've seen that:

Breathing rate increases with exercise intensity
This happens because working muscles need more oxygen and produce more carbon dioxide
The body responds by increasing ventilation to maintain homeostasis
Scientific investigations require careful planning, accurate measurements and thoughtful analysis

Understanding this relationship helps explain how our respiratory system adapts to changing demands and maintains the delicate balance needed for cellular respiration.

🧠 Test Your Knowledge!