specialised exchange surfaces

Question 1

why can diffusion alone supply single celled organisms

Answer 1

• their metabolic activity is low so O2 and CO2 demands are low
• SA:V ratio is high

Question 2

why cant diffusion supply multi-cellular organisms

Answer 2

• some cells are too deep within the body
• larger organisms have a lower SA:V ratio
• multicellular organisms have a higher metabolic rate (use up O2 and glucose faster)

Question 3

features of specialised exchange surfaces

Answer 3

• increased SA
• thin layers
• good blood supply
• ventilation to maintain diffusion gradient

Question 4

nasal cavity features

Answer 4

• large SA
• good blood supply (warms the air to body temp)
• hairy lining which secretes mucus to trap pathogens
• moist surfaces (increase humidity of air, reducing evaporation from exchange surfaces)

Question 5

trachea features

Answer 5

• supported by cartilage c-shaped rings (stop trachea from collapsing)
• lined with ciliated epithelium and goblet cells between/below epithelial cells
• contains elastic fibres
• contains smooth muscle

Question 6

globlet cells and cilia

Answer 6

goblet cells
- secrete mucus which traps microorganisms and dust particles
cilia
- hair like
- beat and move mucus away from the lungs, into the throat

Question 7

bronchus

Answer 7

• trachea divides into 2 bronchi in the chest cavity
• smaller pieces of cartilage
• smooth muscle
• elastic fibres
• ciliated epithelium + goblet cells

Question 8

bronchioles

Answer 8

• bronchi divide into many small bronchioles
• smaller ones have no cartilage
• smooth muscle contracts–> bronchioles constrict
• smooth muscle relaxes–> bronchioles dilate
• thin, flattened ciliated/not epithelium layer
• elastic fibres

Question 9

alveoli

Answer 9

• tiny air sacs
• layer of thin, flattened epithelial cells (1 cell thick),(alveolar epithelium)
• collagen, elastic fibres (elastin)

Question 10

elastic fibres

Answer 10

• trachea, bronchi, bronchioles, alveoli
• breathing in–> lungs inflate and elastic fibres stretch
• breathing out–> fibres recoil and push air out

Question 11

smooth muscle

Answer 11

• trachea, bronchi, bronchioles
• allow their diameter to be controlled
• exercise–> smooth muscle relaxes, widening the tube–> less resistance to air flow

Question 12

cartilage

Answer 12

• trachea, bronchi
• provide support
• strong
• flexible
• stops them collapsing when you breathe in and pressure drops