This key facts covers The Breathing Mechanism within Gas Exchange in Humans for GCSE Biology. Lung structure, alveoli adaptations, breathing mechanism, gas transport in blood, and effects of smoking It is section 5 of 19 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
The Breathing Mechanism
Inspiration (Breathing In)
Step 1: Diaphragm contracts and flattens (moves down)
Step 2: External intercostal muscles contract, lifting ribs up and out
Step 3: Chest cavity volume increases
Step 4: Pressure inside lungs decreases (below atmospheric pressure)
Step 5: Air rushes in through airways to equalize pressure
Expiration (Breathing Out)
Step 1: Diaphragm relaxes and returns to dome shape (moves up)
Step 2: External intercostal muscles relax, ribs move down and in
Step 3: Chest cavity volume decreases
Step 4: Pressure inside lungs increases (above atmospheric pressure)
Step 5: Air is pushed out through airways
Note: Normal expiration is passive (requires no energy), but forced expiration involves contraction of internal intercostal muscles and abdominal muscles.
Practice questions for Gas Exchange in Humans
Which is the correct order of structures air passes through to reach the lungs?
Explain how the structure of alveoli is adapted for efficient gas exchange.
Quick recall flashcards
What are alveoli?
Tiny air sacs in the lungs where gas exchange takes place - oxygen enters the blood and carbon dioxide leaves
What is the trachea?
The main airway (windpipe) that carries air from the throat to the lungs, reinforced with cartilage rings