Instructions
Your lungs are amazing organs that allow you to breathe. The amount of air your lungs can hold is called lung capacity. In this activity, you will learn about the different ways we measure lung volume and then follow the procedure for a simple experiment you can do at home to estimate your own lung capacity.
Part 1: Understanding Lung Volumes
Match the term on the left with the correct definition on the right. Write the letter of the correct definition in the blank space.
- Tidal Volume (TV) _____
- Vital Capacity (VC) _____
- Residual Volume (RV) _____
- Total Lung Capacity (TLC) _____
- A. The maximum amount of air a person can exhale after taking the deepest breath possible.
- B. The total volume of air the lungs can hold. It is the sum of Vital Capacity and Residual Volume.
- C. The amount of air that moves in and out of the lungs during a normal, relaxed breath.
- D. The amount of air that always remains in the lungs, even after exhaling as forcefully as you can. This prevents the lungs from collapsing.
Part 2: Estimating Your Vital Capacity
This experiment uses the water displacement method to estimate your vital capacity. You will measure the amount of water pushed out of a bottle by the air you exhale.
Materials Needed:
- A large plastic bottle with a cap (a 2-liter soda bottle works well)
- A large tub, basin, or sink that can hold water
- A flexible plastic tube or a long straw
- A measuring cup or graduated cylinder
- Water
Procedure:
- Use your measuring cup to determine the total volume of your plastic bottle. Fill it with water, pouring it out into the measuring cup and adding the amounts until the bottle is empty. Record this total volume. Total Bottle Volume: _________ mL
- Fill the plastic bottle completely to the brim with water. Screw the cap on tightly.
- Fill the large tub or sink about halfway with water.
- Turn the bottle upside down and place the top of it under the surface of the water in the tub. Unscrew and remove the cap while the bottle opening is still underwater. Try not to let any air bubbles enter the bottle. The water should stay inside the bottle.
- Carefully slide one end of the flexible tube or straw into the opening of the bottle. Make sure the opening of the tube is inside the bottle and not blocked.
- Take the deepest breath you possibly can, filling your lungs completely.
- Pinch your nose, put your mouth on the other end of the tube, and exhale all the air from your lungs into the tube. Exhale as much air as you can until you can't push out any more. Be careful not to inhale any water!
- The air you exhaled will be trapped in the bottle, pushing water out.
- While keeping the bottle upside down, screw the cap back on tightly before lifting it out of the water.
- Place the bottle upright on a flat surface. The volume of air now at the top of the bottle is equal to your Vital Capacity.
- To measure this volume, carefully pour the remaining water from the bottle into your measuring cup. Record this volume.
- Subtract the volume of the remaining water from the Total Bottle Volume you recorded in Step 1. The result is your estimated Vital Capacity for this trial.
Part 3: Data and Analysis
Good scientific practice involves repeating experiments to ensure your results are reliable. If possible, repeat the experiment two more times (for a total of three trials) and record your data below.
| Measurement | Trial 1 | Trial 2 | Trial 3 |
|---|---|---|---|
| A. Total Bottle Volume (mL) | |||
| B. Volume of Water Left in Bottle (mL) | |||
| C. Estimated Vital Capacity (A - B) (mL) |
Analysis Questions
Answer the following questions based on your experiment and what you've learned.
- Calculate your average Vital Capacity from the three trials. (Add the Vital Capacity from Trial 1, 2, and 3, then divide by 3). Show your work.
- Why is taking an average of multiple trials a better scientific practice than just using the result from a single trial?
- This experiment measures your Vital Capacity, not your Total Lung Capacity. Which lung volume is not being measured, and why can't this experiment measure it?
- A person's Residual Volume is typically estimated to be about 1200 mL. Using your average Vital Capacity from question 1, calculate your estimated Total Lung Capacity. (TLC = Vital Capacity + Residual Volume).
- List two factors that could affect a person's lung capacity and briefly explain how.
Answer Key
Part 1: Understanding Lung Volumes
- Tidal Volume (TV) C
- Vital Capacity (VC) A
- Residual Volume (RV) D
- Total Lung Capacity (TLC) B
Part 3: Data and Analysis
(Note: Answers for the data table and questions 1 & 4 will vary based on the student's own results. A sample calculation is provided.)
- Calculate your average Vital Capacity from the three trials.
Sample Answer: If my trials were 2800 mL, 2950 mL, and 2850 mL.
(2800 + 2950 + 2850) / 3 = 8600 / 3 = 2866.7 mL. My average Vital Capacity is 2866.7 mL. - Why is taking an average of multiple trials a better scientific practice than just using the result from a single trial?
Averaging multiple trials helps to minimize the effect of random errors or a single inaccurate measurement. It provides a more reliable and representative result than a single attempt might. - This experiment measures your Vital Capacity, not your Total Lung Capacity. Which lung volume is not being measured, and why can't this experiment measure it?
The Residual Volume (RV) is not being measured. This experiment cannot measure it because residual volume is the air that you cannot physically force out of your lungs; it always remains inside. - A person's Residual Volume is typically estimated to be about 1200 mL. Using your average Vital Capacity from question 1, calculate your estimated Total Lung Capacity.
Sample Answer using the average from above:
TLC = 2866.7 mL (Vital Capacity) + 1200 mL (Residual Volume) = 4066.7 mL. - List two factors that could affect a person's lung capacity and briefly explain how.
(Any two of the following or other logical answers are acceptable)
- Height/Size: Taller or larger individuals generally have larger thoracic cavities and therefore larger lungs and a greater lung capacity.
- Fitness Level: Regular aerobic exercise (like running or swimming) can strengthen respiratory muscles and increase vital capacity.
- Age: Lung capacity typically increases through childhood and adolescence, peaks in early adulthood, and then gradually declines with age.
- Altitude: People living at high altitudes, where there is less oxygen, often develop a larger lung capacity over time to compensate.
- Health/Smoking: Smoking and respiratory illnesses like asthma can damage lung tissue and reduce lung capacity.