Breathing in living organisms
In cells nutrients (proteins, fats, carbohydrates) are broken down with oxygen, releasing energy and carbon dioxide; this energy is used for growth, movement and life processes. So organisms take in oxygen and give out carbon dioxide. Plants breathe with all their organs: stem, leaf and flower take oxygen from the air, roots from the air between soil particles (so loosening soil helps). Gases enter and leave through the leaf’s stomata. Molluscs and fish breathe with gills; reptiles, birds and mammals with lungs. Human airways: nasal cavity (air is cleaned, moistened and warmed), pharynx, larynx (with vocal cords), trachea, bronchi and lungs. When we breathe in, the chest expands and air enters the lungs; in the lungs gas exchange happens by diffusion: oxygen passes into the blood and carbon dioxide from the blood into the lungs; when we breathe out the chest narrows. In a crowded room oxygen runs low, so rooms need airing.
Small investigation: 1) count your breaths for 1 minute at rest; 2) do 10 squats and count again; 3) rest 2 minutes and count again; draw a graph of the results. Put your hand on your chest and feel it expand as you breathe in. Breathe out in front of a mirror or cold glass and watch the vapour form. Safety: if you feel dizzy, stop and sit down; pupils with asthma or heart conditions skip the exercise and only take part in counting.