CAIE A-Level Biology 8.1.6 Blood Vessel Structure and Function

Marking guidance:

allow tissue fluid / fluid surrounding cells, instead of (smooth muscle) cells allow, blood / plasma, for capillary

allow $\mathrm{O}_{2}$ for oxygen and $\mathrm{CO}_{2}$ for carbon dioxide

any three from:

capillary function

1 named, substance / type of substance, that is supplied to smooth muscle cells or is a product removed from the cells ;

e.g. (supply) oxygen / nutrients / glucose / amino acids / cell-signalling molecule

e.g. (removes)_carbon dioxide / lactic acid / waste

A exchange of respiratory gases (between capillary and cells)

I plasma proteins into tissue fluid

structure to function

2 thin wall / AW, so short distance ;

R capillary is thin

3 endothelial pores / fenestrations, for more efficient passage / AW ;

A gaps, between / within, (endothelial) cells (of capillary wall)

A increases, quantity / rate of supply (of substances)

A endothelial pores for formation of tissue fluid (around cells)

R if blood leaves to make tissue fluid

4 (endothelial) pores / AW, for passage of, phagocytes / monocytes / macrophages / neutrophils ;

5 small (size) / narrow diameter, to reach cells / so (all) cells are close ;

A value in range $5-10 \mu \mathrm{~m}$

A small size / narrow lumen, slows (rate of) blood flow

6 detail about red blood cell and, respiratory gases / gas exchange / oxygen / carbon dioxide ;

e.g. narrow lumen slows red blood cell movement for uptake of oxygen

slows red blood cell movement to increase time for exchange of gases

only one red blood cell fits (at a time) so short diffusion distance

red blood cells are close to (muscle) cells for gas exchange

red blood cells squeeze through, (so) distance for oxygen to reach cells is minimised