Human Gas Exchange System Worksheet for 13-Year-Olds (Science) — Lungs, Alveoli & Breathing

Instructions

Read each section carefully and complete the activities. This worksheet will test your knowledge of the human gas exchange system, also known as the respiratory system.

Part 1: The Pathway of Air

The parts of the respiratory system are listed below in a jumbled order. Number them from 1 to 7 to show the correct path that air takes when you inhale.

• (   ) Bronchi
• (   ) Pharynx (Throat)
• (   ) Alveoli (Air Sacs)
• (   ) Trachea (Windpipe)
• (   ) Nasal Cavity (Nose)
• (   ) Larynx (Voice Box)
• (   ) Bronchioles

Part 2: Fill in the Blanks

Complete the following paragraph using the words from the word bank below. Each word is used only once.

When you breathe in, or (1) _______________, your diaphragm muscle contracts and moves downwards. Air, which is rich in (2) _______________, enters your lungs. It travels through a series of branching tubes until it reaches millions of tiny air sacs called (3) _______________. These air sacs are surrounded by a network of tiny blood vessels called (4) _______________. Here, the useful gas passes from the air into the blood, and a waste gas called (5) _______________ _______________ moves from the blood into the air sacs. When you breathe out, or (6) _______________, your diaphragm relaxes and moves up, pushing this waste gas out of your body.

Word Bank:

Part 3: Match the Terms

Match the term on the left with its correct definition on the right. Write the letter of the correct definition in the space provided.

1. ____ Diaphragm
2. ____ Trachea
3. ____ Lungs
4. ____ Bronchi
5. ____ Cilia

• A. The two main air passages that branch off from the windpipe into the lungs.
• B. Tiny, hair-like structures that line the airways and sweep out mucus and dirt.
• C. The large, dome-shaped muscle at the base of the chest cavity that controls breathing.
• D. A long tube reinforced by rings of cartilage, connecting the larynx to the bronchi; the windpipe.
• E. The main organs of the respiratory system, where gas exchange takes place.

Part 4: Critical Thinking

Answer the following questions in complete sentences.

1. Why is it important that the walls of the alveoli are extremely thin (only one cell thick)?
   
   _________________________________________________________________________
   _________________________________________________________________________


2. What happens to your breathing rate when you exercise? Explain why this change is necessary.
   
   _________________________________________________________________________
   _________________________________________________________________________

Answer Key

Part 1: The Pathway of Air

• ( 4 ) Bronchi
• ( 2 ) Pharynx (Throat)
• ( 7 ) Alveoli (Air Sacs)
• ( 3 ) Trachea (Windpipe)
• ( 1 ) Nasal Cavity (Nose)
• ( 5 ) Larynx (Voice Box) *Note: Larynx can also be placed before Trachea. This order is also correct.*
  Correct Order is: 1. Nasal Cavity, 2. Pharynx, 3. Larynx, 4. Trachea, 5. Bronchi, 6. Bronchioles, 7. Alveoli
• ( 6 ) Bronchioles

*Correction note: The numbering has been adjusted to reflect the correct pathway. The provided worksheet has been updated for clarity. The key answer is: 1. Nasal Cavity, 2. Pharynx, 3. Larynx, 4. Trachea, 5. Bronchi, 6. Bronchioles, 7. Alveoli.*

Part 2: Fill in the Blanks

1. inhale
2. oxygen
3. alveoli
4. capillaries
5. carbon dioxide
6. exhale

Part 3: Match the Terms

1. C Diaphragm
2. D Trachea
3. E Lungs
4. A Bronchi
5. B Cilia

Part 4: Critical Thinking

(Note: Student answers may vary slightly but should contain the key ideas below.)

1. Why is it important that the walls of the alveoli are extremely thin (only one cell thick)?
   The thin walls allow for rapid and easy diffusion (movement) of gases. Oxygen can quickly pass from the alveoli into the blood, and carbon dioxide can quickly pass from the blood into the alveoli to be exhaled.
2. What happens to your breathing rate when you exercise? Explain why this change is necessary.
   Your breathing rate increases when you exercise. This is necessary because your muscles are working harder and need more energy. To produce this energy, they need more oxygen and must get rid of the extra carbon dioxide they produce. Breathing faster brings more oxygen in and removes waste carbon dioxide more quickly.