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in one minute
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Air
moves into the tracheae through pores on the surface called spiracles
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Oxygen diffuses from the air, through the spiracles along the trachea and the
tracheoles to the cells
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Carbon dioxide leaves the cells down its own concentration gradient towards the
spiracles to be released into the atmosphere by the reverse pathway
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Carbon dioxide levels rise due to respiration, causing the spiracles to open
wider, increasing the rate of diffusion of gases in the tracheal system
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Thursday, 3 January 2019

In large or very active insects, body muscles may contact to compress the trachea
forcing air out of them
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During increased activity, anaerobic respiration often occurs, producing lactic acid
in cells, lowering the water potential of the cells and so some of the water in the
ends of the tracheoles moves into the cells by osmosis
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Gaseous Exchange In Fish
In bony fish gas exchange occurs over the surface of the gills which consists of four
pairs of gill arches, consisting of many gill filaments, protected by the operculum
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The thin barrier consists of two cell layers:


- the epithelial layer of the gill lamellae

- the endothelial layer of the blood capillaries

• a circulatory system which ensures a continual flow of blood through the
respiratory surface to absorb oxygen and remove carbon dioxide and so
maintaining a high diffusion gradient

• a ventilation mechanism which provides a continual flow of water over the gills
bringing more oxygen and removing carbon dioxide and so maintaining a Hugh
diffusion gradient

• a countercurrent system which ensures that blood continually meets water with a
higher oxygen concentration so a high diffusion gradient is maintained along the
whole length of the lamellae


Gaseous Exchange In Plants
Plants need carbon dioxide for photosynthesis, which produces oxygen as a waste
gas
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Photosynthesis and respiration maintain diffusion gradient by using and
producing oxygen and carbon dioxide
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Gases diffuse down through the stomata in the
epidermis of the leaves between the guard cells, down a concentration gradient and
rapidly through the intercellular air spaces
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Stomata can open to allow the exchange of gases and can close if the plant is
losing too much water
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Digestion of Carbohydrates In Humans
Digestion is the process in which large molecules a

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