gaseous exchange
unicellular
uni = 1 cell
obtain o2 through diffusion
has a much larger SA:V ratio
multicellular
multi = many cells
cannot rely on diffusion
has to have evolved a specialised exchange surface
good exchange surface features
• large SA
• maintains a steep concentration gradient -> constantly removed on one side and fresh supply on the other
• thin wall -> short diffusion distance
lungs are needed because
small SA:V ratio
diffusion is not sufficient to meet cellular demands
trachea adaptations
•c-shaped rings of cartilage -> holds airways open, allows oesophagus to expand
•smooth muscle -> expand of restricted airway, contsrict airways
•ciliated epithelial cells -> waft mucus up to the mouth
• goblet cells -> secrete mucus
bronchus adaptations
•trachea splits into two bronchi
•bronchi divides into many bronchioles, then feed into many alveoli
ciliated epithelial tissue is made up of ciliated epithelial cells and goblet cells
cartilage
• keeps airway open -> support
• rings are in blocks so small amount of bending can happen
smooth muscle
• involuntary
• controls airflow into and out of the airway
• contracts to reduce lumen size
elastic fibres
• stretch during inspiration (breathing in) and recoil during expiration (breathing out)
• aids the forcing out of air during expiration
goblet cells
• in epithelium
• secrets mucus to trap foreign particles
ciliated epithelium
have cilia that waft mucus and foreign particles up to the mouth
simple squamous epithelial cell
very thin and flat -> gas exchange
e.g. alveoli
simple columnar epithelial cells
in trachea, long and tall
alveoli
• about 300 million in lungs -> large SA
• thin squamous epithelial cells -> short diffusion distance
• lots of capillaries -> good blood supply, steep concentration gradient
• moist -> dissolves gases, contains surfactant
• elastic fibres -> recoils during expiration
gaseous exchange when breathing in
the concentration of oxygen is higher in the alveoli than in the blood, so it diffuses into the blood DOWN a concentration gradient
inspiration (breathing in)
• diaphragm contracts to pull lungs down
• external intercostal muscles contract and pull ribcage up and out, increasing volume of pleural cavity
• because volume increases, pressure inside lungs decreases relative to outside -> air rushes into lungs to equalise pressure
expiration (breathing out)
• external intercostal muscles and diaphragm relax and decrease the volume of the pleural cavity, moving the rib cage in and down
• the pressure inside the lungs increases relative to outside -> air moves out
spirometer
measures changes in lung volume
spirometer reading
tidal volume - beginning
inspiratory reserve volume - below TV
expiratory reserve volume - above TV
residual volume - amount above ERV
vital capacity - TV + IRV + ERV
lung volume - VC + RV
insect ventilation
• have holes in their side called spiracles
• spiracles can be opened and closed by sphincters
• spiracles lead to a system of tracheae, tracheoles and the end of tracheoles are filled with water
• tracheae oh hold open by rings of chitin
fish ventilation
• gills have long, thin lamellae - rich blood supply and large SA
• find lamellae on filaments
• filaments are stacked in gill plates - large SA
• water passes over the gills to allow gas exchange as the fish swims
• when stationery, the fish can open and close mouth and a operculum to ventilate gills
fish ventilation process
• mouth is opened and flaw of buccal cavity is lowered, this increases volume of buccal cavity
• pressure in the cavity drops and water moves to the buccal cavity
• the opercular valve is shut
• floor of the buccal cavity starts to move up, increasing pressure, so water moves from the buccal cavity over to the gills
• mouth closes, operculum opens, sides of opercular cavity move inwards -> increases the pressure in the opercular cavity, force water over gills and out of the operculum