MYP Biology: The Respiratory System & Breathing

You need to know the structure of the respiratory system (nose, trachea, bronchi, bronchioles, alveoli), the mechanics of breathing (diaphragm and intercostal muscles changing chest volume and pressure), and gas exchange at the alveoli by diffusion. You also need to link breathing rate to exercise and cellular respiration.

Breathing is the physical, mechanical process of moving air in and out of the lungs — it's what you can see and measure. Respiration is the chemical process inside cells that releases energy from glucose, using the oxygen breathing supplies. Mixing these two up is the single most common mistake in this unit.

Inhalation: the diaphragm contracts and flattens, intercostal muscles pull the ribcage up and out, chest volume increases, pressure inside drops below atmospheric pressure, and air rushes in. Exhalation reverses this — muscles relax, volume decreases, pressure rises above atmospheric, and air is pushed out.

Oxygen diffuses from the alveoli (high concentration) into the blood in surrounding capillaries (low concentration), and carbon dioxide diffuses the opposite way, from blood into alveoli, to be exhaled. This happens by simple diffusion down concentration gradients across the thin alveolar walls.

A large surface area means more diffusion can happen at once, so more oxygen enters the blood and more carbon dioxide leaves it per second. With around 300 million alveoli in adult human lungs giving a combined surface area roughly the size of a tennis court, gas exchange keeps pace with the body's demand for oxygen even during exercise.

Expect 'identify' and 'label' for structures, 'describe' for the sequence of breathing mechanics, 'explain' for linking structure to function or pressure to volume, and 'evaluate' or 'discuss' if the unit is assessed against Criterion D (Reflecting on the impacts of science), often tied to a real-world respiratory disease.

Most schools assess this unit against Criterion A (Knowing and understanding) through structure-labelling and gas-exchange questions, and Criterion D (Reflecting on the impacts of science) through a task on smoking, asthma or air pollution and its effect on lung function. Some units also use Criterion C if there's a practical investigation on breathing rate.

Structure your answer in the same order the examiner will mark it: name the structure or process, state what change happens, then explain the mechanism or consequence. For a 4-mark 'explain' question, aim for four distinct, linked points rather than one long paragraph repeating the same idea.

Learn the pathway air actually travels, in order, rather than a random list: nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli. Saying it aloud as a sentence, or sketching it from memory three times, embeds the sequence far better than re-reading a labelled diagram passively.

Practise explaining inhalation and exhalation out loud, as if teaching someone else, using the words 'diaphragm', 'intercostal muscles', 'volume' and 'pressure' every time. If you can explain both halves of the breathing cycle without checking notes, you've got the mechanism — most students only ever memorise inhalation and freeze on exhalation in the exam.

Usually it's not understanding that's missing — it's precision in the answer. Students often say 'the lungs expand' without naming which muscles cause it, or say 'oxygen goes into the blood' without saying 'by diffusion down a concentration gradient'. Examiners mark the specific biological vocabulary, not just the general idea.

It's a mid-difficulty unit — the vocabulary is heavy (diaphragm, intercostal, alveoli, diffusion) but the underlying logic is straightforward once your child sees the volume-pressure-diffusion chain as one connected story rather than three separate facts to memorise. Most students who struggle are missing the mechanism, not the terminology.

Ask your child to explain, out loud, why breathing rate increases during exercise and see if they connect it to cellular respiration needing more oxygen. If they can teach you the diaphragm-volume-pressure-diffusion chain unprompted, they're genuinely ready; if they only recall isolated facts, that's the gap worth practising before the assessment.