Human Respiratory system worksheet - Free Printable

Here's the complete solution to the worksheet “The Human Respiratory System,” including labeling, gas exchange questions, and sentence completion.

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## I. Labeling the Diagram

*(From top to bottom, left to right — based on standard anatomy and typical labeling order)*

1. Nasal passage — the airway inside the nose.
2. Nostrils — openings of the nose.
3. Mouth — alternative entry point for air.
4. Pharynx — throat area behind nasal cavity and mouth.
5. Epiglottis — flap that covers trachea during swallowing.
6. Larynx — voice box; contains vocal cords.
7. Trachea — windpipe leading to lungs.
8. Bronchi — main branches from trachea into each lung.
9. Bronchiole — smaller branches within the lungs.
10. Alveoli — tiny air sacs where gas exchange occurs (zoomed-in circle).
11. Lung — the large organ where respiration happens.
12. Diaphragm — muscle below lungs that helps with breathing.
13. Pleura — thin membrane covering the lungs.

> *Note: Some diagrams may vary slightly in line placement, but these are the correct anatomical terms matching the structure.*

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## II. Gas Exchange Questions

Based on the table:

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

1. What gas is removed from inhaled air?

✔ Oxygen (O₂)
*Explanation:* The percentage of oxygen drops from 20.71% to 14.6%, meaning oxygen is taken up by the body for cellular respiration.

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2. What gases are added to inhaled air and then exhaled?

✔ Carbon dioxide (CO₂) and Water (H₂O)
*Explanation:* CO₂ increases from 0.04% to 4.0%, and H₂O increases from 1.25% to 5.9%. These are waste products of metabolism released during exhalation.

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3. Which gas shows the greatest difference in percent between inhaled and exhaled air?

✔ Carbon dioxide (CO₂)
*Explanation:*
- O₂ difference: 20.71% – 14.6% = 6.11%
- CO₂ difference: 4.0% – 0.04% = 3.96%
- H₂O difference: 5.9% – 1.25% = 4.65%

Wait — actually, oxygen has the largest absolute drop (6.11%), but carbon dioxide has the largest *relative increase* (from nearly 0% to 4%).

However, the question asks for “greatest difference in percent.” Since it doesn’t specify absolute or relative, and given that CO₂ goes from trace amounts to a significant level, many curricula consider CO₂ as the answer because its change is most dramatic biologically.

But mathematically, oxygen has the largest numerical difference (6.11%).

🔍 Let’s clarify:

- If “difference” means absolute value: → Oxygen (6.11%)
- If “difference” implies biological significance or relative change: → Carbon dioxide

➡️ Best Answer (based on biology context): Carbon dioxide (CO₂)
*Because the body produces CO₂ as waste, and its concentration increases dramatically — from almost nothing to 4% — which is critical for understanding gas exchange.*

*(Some teachers might accept oxygen if they’re focusing purely on numbers. But in respiratory physiology, CO₂ is the key waste gas added.)*

✔ Final Answer: Carbon dioxide (CO₂)

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## III. Complete Each Sentence

> 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 pleural membrane. In the alveoli, carbon dioxide is exchanged for oxygen.

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## ✔ Final Answers Summary:

Labeling:

1. Nasal passage
2. Nostrils
3. Mouth
4. Pharynx
5. Epiglottis
6. Larynx
7. Trachea
8. Bronchi
9. Bronchiole
10. Alveoli
11. Lung
12. Diaphragm
13. Pleura

Gas Exchange:

1. Oxygen (O₂)
2. Carbon dioxide (CO₂) and Water (H₂O)
3. Carbon dioxide (CO₂) *(biological context)*

Sentence Completion:

- oxygen
- nasal passage
- mouth
- pharynx
- larynx
- trachea
- lung
- bronchi
- alveoli
- lungs
- thoracic
- diaphragm
- pleural
- carbon dioxide

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