(a) the need for specialised exchange surfaces
To include surface area to volume ratio (SA:V), metabolic activity, single-celled and multicellular
organisms.
NOTES
o larger organisms require specialised exchange surfaces to ensure all cells can obtain
sufficient nutrients and gases,
o larger organims have a smaller SA:V which means that there is a long diffusion distance,
o oxygen cannot diffuse quick enough to meet their metabolic needs as they have higher
metabolic activity.
(b) the features of an efficient exchange surface
To include: • increased surface area – root hair cells • thin layer – alveoli • good blood
supply/ventilation to maintain gradient – gills/alveolus.
NOTES
o root hair cells have a large surface area to increase the rate of diffusion,
o alveoli walls made of squamous epithelial cells which forms a thin diffusion pathway and
shortens the diffusion distance,
o alveolus and gills have a good/rich blood supply to maintain the concentration gradient,
o alveoli have a high oxygen concentration and blood has a low oxygen concentration
which makes oxygen diffuse into blood.
(c) the structures and functions of the components of the mammalian gaseous exchange system
To include the distribution and functions of cartilage, ciliated epithelium, goblet cells, smooth
muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli.
NOTES
o goblet cells secrete mucus which trap dust/bacteria that enters the lungs,
o ciliated epithelial cells waft mucus to the top of the trachea where it is
swallowed/coughed up,
o elastic fibres recoil to their original shape to expel air and prevent lungs from bursting,
o smooth muscle in bronchioles contract to constrict the airways to prevent harmful
substances from entering,
o cartilage provides strength and support to the trachea which prevents collapse during
inhalation,
o trachea contains c-shaped rings of cartilage, smooth muscle, ciliated epithelial and
elastic fibres,
o bronchi contains cartilage, smooth muscle, elastic fibres, ciliated epithelial,
o bronchiole contains smooth muscle, elastic fibres and squamous epithelial,
o alveoli contains elastic fibres and squamous epithelial.
(d) the mechanism of ventilation in mammals
To include the function of the rib cage, intercostal muscles (internal and external) and
diaphragm.
NOTES
, o EXAM TIP: when talking about ventilation you must discuss DRVPPG (diaphragm, ribs,
volume, pressure, pressure gradient),
Inspiration:
1. diaphragm contracts and flattens,
2. ribs move up and out, the external intercostal muscles contract and the internal relax,
3. volume in the thorax increases,
4. pressure in the thorax decreases,
5. air moves in along the pressure gradient.
2. Expiration:
1. diaphragm relaxes and rises,
2. ribs move down and in, external intercostal muscles relax and internal contract,
3. volume in the thorax decreases,
4. pressure in the thorax increases,
5. air moves out along the pressure gradient.
(e) the relationship between vital capacity, tidal volume, breathing rate and oxygen uptake
To include analysis and interpretation of primary and secondary data e.g. from a data logger or
spirometer.
NOTES
o tidal volume - volume of air breathed in and out in a single breath at rest (usually
500cm3),
o vital capacity - maximum volume of air that can be breathed in and out in a single
breath (4 to 4.5dm3),
o breathing rate - number of breaths per minute (peak to peak),
o total air breathed per minute (pulmonary ventilation) is: tidal volume x breathing rate,
o oxygen uptake - volume of oxygen taken up by the body/lungs,
o oxygen uptake calculated by finding gradient of trace (change in y/change in x),
o air breathed into spirometer has CO2 removed by soda lime, the oxygen is used for
aerobic respiration.
(f) the mechanisms of ventilation and gas exchange in bony fish and insects
To include: • bony fish – changes in volume of the buccal cavity and the functions of the
operculum, gill filaments and gill lamellae (gill plates); countercurrent flow • insects – spiracles,
trachea, thoracic and abdominal movement to change body volume, exchange with tracheal
fluid.
NOTES
o fish have many lamellae (gill filaments) so there is a large surface area for gas exchange,
o presence of secondary lamellae on primary lamellae which also increases SA,
o rich/good blood supply which creates short diffusion distance between blood and water,
o blood flows in a countercurrent system to maintain concentration gradient for faster
diffusion.
Fish ventilation:
6. as fish open mouth, increased volume and decreased pressure in buccal cavity,
7. water forced into mouth along pressure gradient,
8. when fish closes mouth, decreased volume and increased pressure in buccal cavity,
9. water forced over gill filaments and out of operculum.
