Summary of gas exchange in fish gills

1.Fish have developed specialised gas-exchange organs called gills, which are composed of thousands of filaments.

2.The filaments in turn are covered in feathery lamellae which are only a few cells thick and contain blood capillaries.

3.This structure gives a large surface area and a short distance for gas exchange.

4.Water flows over the filaments and lamellae, and oxygen can diffuse down a concentration gradient the short distance between water and blood, whilst CO2 diffuses in the opposite direction, also down its concentration gradient.

5.Each gill is covered by a muscular flap (the operculum) on the side of a fish's head.

6.The gills are so thin that they cannot support themselves without water, so if a fish is taken out of water after a while the gills will collapse, the SA/Vol ratio falls, and the fish suffocates.

DNA workshop!

Bring in your slips ASAP as places are starting to fill up!

Wonders of life expanding universe

http://www.bbc.co.uk/iplayer/episode/b01qm913/Wonders_of_Life_Expanding_Universe/

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Thanks
Ms Timms :)

SA/vol ratio summary

As organisms get bigger their volume increases by the cube of their size, whilst their surface area increases by the square of their length

= so volume increases much faster than surface area.

As the size of the organism increases the surface area to volume ratio gets smaller

SA/vol ratio practice question

 

Explain the link between the size of an organism and the way in which its cells are supplied with oxygen.

(6)

mark scheme:
Note: Accept converse argument throughout

Small organisms have large surface/volume ratio;

as, for example, most protoctista/single-celled
organisms/platyhelminths/cnidaria; diffusion/exchange over body surface/skin;

(the need for) specialised respiratory/gas-exchange surfaces in larger
animals;

diffusion is a slow process;

cells of larger organisms are a long way from gas exchange surface;

must be supplied by transport system/circulatory system/blood; 

max 6

Surface area to volume ratio images