The diagram below shows a part of the gills of a bony fish  

a.   Identify the following features shown in the diagram  
  i) X  
    Filament (1)
  ii) Y  
    Capillary (1)
  iii) Z  
    (Secondary) Lamellae (1)
b.   Show on the diagram the direction of blood flow  
    The arrow must be in the opposite direction to the arrows showing water flow (blue arrows) (1)
c.   Give two adaptions that can be seen in the diagram that make the gill an effective gas exchange surface  
  • Large Surface area
  • Many capilaries
  • Short diffusion distances between blood and water