Limiting water loss and structure of human gas-exchange system

How do insects limit water loss

• small surface area to volume ratio - minimise area over which water is lost

• waterproof coverings - chitin covered in a waterproof cuticle

• spiracles - openings of the tracheae at body surface that can be closed to reduce water loss

What are xerophytes?

plants that are adapted to living in areas where water is in short supply

Plant modification to reduce water loss

• thick cuticle - waterproof barrier

• rolling up of leaves - traps a region of still air within the rolled leaf which is saturated with water vapour so there is no water potential gradient

• hairy leaves - traps moist air next to leaf surface

• stomata in pits - traps still, moist air

• reduced surface area to volume ratio of leaves - slower rate of diffusion

Gas exchange system components

• alveoli

• bronchioles

• bronchi

• trachea

• lungs

Lungs

pair of lobed structures made up of a series of highly branched tubules called bronchioles which end in tiny air sac called aleoli

Trachea

• flexible airway supported by rings of cartilage

• walls made of muscle lined with ciliated epithelium and goblet cells

  
  

Bronchi

• two divisions of the trachea

• produce mucus to trap dirt particles

• have cilia that move dirt-laden mucus towards throat

Bronchioles

• branching subdivisions of bronchi

• walls made of muscle lined with epithelial cells

• muscle allows them to constrict so they can control flow of air in and out the alveoli

Alveoli

• minute air sacs at end of bronchioles

• lined with epithelium

• stretch (elastic fibres) when breathing in

• spring back during breathing out