Gas Exchange in Fish Aqa book p 180-1

Homework Colour and construct gill – see exemplar Text p.181 red q1,2,3,4 183 red 183 green Learn key words – lamellae, filaments, counter current exchange, Extension – use the list of features of an exchange surface p.177 to describe how gills are adapted for efficient exchange

Objectives What is the structure of fish gills? How is water passed along fish gills? What is the difference between parallel flow and countercurrent flow? How does countercurrent flow increase the rate of gas exchange?

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buccal cavity operculum (shown partly cut away) gills

Water flows into the buccal cavity Operculum Water is ejected through the open operculum Gills

What is the structure of fish gills? Read p.180 You will make a gill for homework for your notes

Bony gill arch Afferent artery (deoxygenated blood) Efferent artery (oxygenated blood) Gill filament Gill plates (secondary lamellae) Stacked filaments Extensive network of capillaries within the gill plates

Water flows across the gill plates in the opposite direction to the flow of blood within the capillaries of the plates This provides a countercurrent exchange mechanism such that an oxygen concentration gradient persists along the length of the gill plates

How is water passed along fish gills? P What is a counter current flow? 2.Where on the gill does diffusion occur? 3.How much of the oxygen in the water is taken up by the gill?

What is the difference between parallel flow and countercurrent flow? During countercurrent flow, the concentration gradient for oxygen persists along the length of the gill plate allowing for maximum absorption of oxygen into the blood During parallel flow, the initial steep concentration gradient for oxygen declines such that the maximum saturation of the blood is limited to 50% Numbers = oxygen concentrations

What is the difference between parallel flow and countercurrent flow? Criticise the colours!!

Adaptations of gills summary; Large surface area – many gill filaments and gill plates Thin – short diffusion distance: - capillary and lamellae walls are only one cell thick such that there are only two cell layers between the water and the blood flowing in the capillaries. Circulating blood maintains the concentration gradient of carbon dioxide and oxygen Counter current flow means the concentration gradient is maintained over the full surface of the gill Fish ventilates the gills maintaining the concentration gradient of carbon dioxide and oxygen Permeable so oxygen and carbon dioxide can pass over

Fish gill observation Teacher to dissect fish WEAR SAFETY SPECS Each pair take a gill in a petri dish of water Observe with a viewer/LP microscope(spot the lamellae!) Observe a small portion of the lamellae using a microscope (spot the blood cells+ vessels) WASH HANDS Requirements Safety specs Teacher dissection stuff (scissors, seeker) Each pair Petri dish Viewer Sharp scissors Slide and coverslip microscope

Fish dissection Gill rakers (filter water) Gill filaments (large surface area) Gill bar

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