Page 136 - Biology Form Two
P. 136
Biology for Secondary Schools
Part Adaptive features Functions
Mucus lining and cilia Trap and filter dust and
micro-organisms
Lungs Spongy with numerous air To hold inhaled air
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spaces (alveoli)
Alveoli Numerous in number Provide large surface area
(singular, alveolus) for gas exchange
Thin membranes Reduce distance for
diffusion of gases
Moist surface Enables gases to dissolve
into solutions before
diffusing
Have dense network of Transport oxygen from the
capillaries alveoli to the tissues and
carbon dioxide from the
tissues to the alveoli
Constantly contain air Maintain shape to avoid
collapsing
Pleural membrane Contain pleural fluid Lubricates the membranes
so that the lungs can slide
smoothly over the thoracic
cavity during breathing
Ribs Made of hard bone tissue Protect the lungs from
mechanical injury
Intercostal muscles Move antagonistically: when Allow expansion and
one muscle contracts the other contraction of the thoracic
relaxes and vice versa cavity
Diaphragm Consit of a dome-shaped sheet Separates the thorax from
of skeletal muscle the abdomen
Allows gas exchange by
becoming dome-shaped or
relaxed
130 Student’s Book - Form Two
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