Explain the mechanism of breathing

Breathing consists of two phases called inhalation and exhalation.


In order for air to be drawn into the lungs during inhalation the volume of the thorax must increase. This is brought about due to the contraction of respiratory muscles. The diaphragm contracts and flattens and the intercostal muscles contract to pull the ribs up and out. The increased volume within the thoracic cavity lowers the pressure within the lungs with respect to the atmospheric pressure. Consequently, air is drawn into the lungs down a pressure gradient.


Inhalation is now complete and the next step is exhalation. The diaphragm relaxes and moves up and the relaxation of the intercostal muscles moves the ribs in and down. This has the effect of decreasing the volume within the thoracic cavity and increasing the pressure within the lungs with respect to atmospheric pressure. As a result, air moves out of the lungs down a pressure gradient.

Lauren M. Mentoring -Medical School Preparation- tutor, Uni Admission...

1 year ago

Answered by Lauren, an A Level Biology tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


£26 /hr

Lorenzo C.

Degree: Biomedical Sciences with Honours in Infectious Diseases (Bachelors) - Edinburgh University

Subjects offered: Biology, Physics+ 1 more


“Hey! I'm Lorenzo and I study Biomedical Sciences with an honours in Infectious Diseases at the University of Edinburgh. I'd be happy to help you with Biology, Chemistry and Physics at GCSE or at A-Level.  I have previous experience tu...”

£20 /hr

Lucy R.

Degree: Health and Human Sciences (Bachelors) - Durham University

Subjects offered: Biology, Maths+ 3 more

English Literature

“I am a first year undergraduate at Durham University. I am studying Health and Human Sciences which is a bridge between science and humanities, combining Anthropology, Biology and Geography! I have always had a hard working ethos and ...”

MyTutor guarantee

£20 /hr

Alice W.

Degree: Psychology (Bachelors) - Bristol University

Subjects offered: Biology, Sociology+ 1 more


“About me Hi my name’s Alice and I’m a Psychology student at the University of Bristol. At A-level I studied Psychology, Sociology and Biology, which meant all my studies complimented each other. This enabled me not only to understand ...”

MyTutor guarantee

About the author

Lauren M.

Currently unavailable: for new students

Degree: Veterinary Medicine (Bachelors) - Cambridge University

Subjects offered: Biology, Maths+ 3 more

.BMAT (BioMedical Admissions)
-Medical School Preparation-

“Hi, I'm Lauren, and I'm a second year veterinary student at Cambridge University. I tutor Maths and Science at GCSE and A-level and can also help with university applications.”

MyTutor guarantee

You may also like...

Other A Level Biology questions

Describe blood supply to the liver?

What's the difference between the cell wall and cell membrane?

What are the two main secondary structures of proteins?

What is the role of ATP in a cell?

View A Level Biology tutors


We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss