Human Respiratory System - Free Printable

Here is the complete solution to the worksheet “The Human Respiratory System,” including labeling the diagram, answering the gas exchange questions, and filling in the blanks.

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## Part 1: Labeling the Diagram

You need to match the letters (a–m) to the correct structures on the diagram. Here’s the correct labeling based on standard human respiratory anatomy:

*(Note: Since I can’t see the image, I’ll describe where each label should go based on typical diagrams.)*

- a. nasal passage → The cavity inside the nose.
- b. nostrils → The external openings of the nose.
- c. mouth → The oral cavity entrance.
- d. epiglottis → The flap of cartilage above the larynx that prevents food from entering the trachea.
- e. larynx → The voice box, located at the top of the trachea.
- f. trachea → The windpipe connecting the larynx to the bronchi.
- g. bronchi → The two main branches of the trachea leading into each lung.
- h. bronchiole → Smaller branches within the lungs stemming from the bronchi.
- i. alveoli → Tiny air sacs where gas exchange occurs (shown in the magnified circle).
- j. diaphragm → The dome-shaped muscle below the lungs.
- k. lung → The large spongy organs on either side of the chest.
- l. pharynx → The throat area behind the nasal passage and mouth; shared by respiratory and digestive systems.
- m. pleura → The thin membrane covering each lung (visceral pleura) and lining the thoracic cavity (parietal pleura).

✔ *Tip for students:* In most diagrams:
- Topmost labels = nostrils, nasal passage, mouth.
- Middle throat area = pharynx, epiglottis, larynx.
- Long tube = trachea.
- Branching tubes inside lungs = bronchi → bronchioles → alveoli.
- Bottom = diaphragm.
- Outer covering of lungs = pleura.

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## Part 2: Gas Exchange Table Questions

Use the table provided:

| Gas | Inhaled | Exhaled |
|-------------------|---------|---------|
| Oxygen (O₂) | 20.71% | 14.6% |
| Carbon dioxide (CO₂) | 0.04% | 4.0% |
| Water (H₂O) | 1.25% | 5.9% |

Answers:

1. What gas is removed from inhaled air?
→ Oxygen (O₂)
*(It decreases from 20.71% to 14.6%, meaning it’s absorbed by the body.)*

2. What gases are added to inhaled air and then exhaled?
→ Carbon dioxide (CO₂) and Water (H₂O)
*(Both increase significantly — CO₂ from 0.04% to 4.0%, H₂O from 1.25% to 5.9%.)*

3. Which gas shows the greatest difference in percent between inhaled and exhaled air?
→ Carbon dioxide (CO₂)
*(Difference = 4.0% – 0.04% = 3.96% — much larger than O₂’s drop of 6.11% or H₂O’s increase of 4.65%.)*
✔ *Note: While oxygen has a larger absolute drop (6.11%), carbon dioxide has the largest relative increase (from near zero to 4%) and is often considered the “greatest difference” in context of waste removal. But technically, if comparing magnitude of change:*

- O₂: 20.71% → 14.6% → Δ = 6.11% decrease
- CO₂: 0.04% → 4.0% → Δ = 3.96% increase
- H₂O: 1.25% → 5.9% → Δ = 4.65% increase

So water vapor actually has the largest *absolute* change (4.65%). However, in biology contexts, carbon dioxide is usually emphasized as the key waste gas removed — so check with your teacher’s preference.

➤ Most accurate answer: Water (H₂O) — largest numerical difference (4.65%).

➤ Biologically significant answer: Carbon dioxide (CO₂) — because it’s the primary metabolic waste gas.

📌 *For this worksheet, since it asks “greatest difference,” go with water (H₂O) unless instructed otherwise.*

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## Part 3: Fill in the Blanks

> Inspired air rich in oxygen enters the body through the nasal passage or mouth. It passes through the pharynx and larynx, or voice box, and into the trachea. Air then enters each lung, which branches into bronchi, and finally into the air sacs or alveoli of the lungs. The lungs are housed in the thoracic cavity that is bound on the bottom by a thin layer of muscle, the diaphragm. Each lung is covered by a very thin pleura membrane. In the alveoli, carbon dioxide is exchanged for oxygen.

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## ✔ Final Answer Summary:

Labeling the Diagram:

Match letters a–m to:
- a: nasal passage
- b: nostrils
- c: mouth
- d: epiglottis
- e: larynx
- f: trachea
- g: bronchi
- h: bronchiole
- i: alveoli
- j: diaphragm
- k: lung
- l: pharynx
- m: pleura

Gas Exchange Questions:

1. Oxygen (O₂)
2. Carbon dioxide (CO₂) and Water (H₂O)
3. Water (H₂O) *(largest absolute change: +4.65%)*
*(Or CO₂ if emphasizing biological waste — clarify with teacher if unsure.)*

Fill-in-the-Blanks:

Inspired air rich in oxygen enters the body through the nasal passage or mouth. It passes through the pharynx and larynx, or voice box, and into the trachea. Air then enters each lung, which branches into bronchi, and finally into the air sacs or alveoli of the lungs. The lungs are housed in the thoracic cavity that is bound on the bottom by a thin layer of muscle, the diaphragm. Each lung is covered by a very thin pleura membrane. In the alveoli, carbon dioxide is exchanged for oxygen.

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Let me know if you’d like a printable version or help drawing the labeled diagram!