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B3 Revision
Exchange of Materials

Active transport is the movement of substances from an area of low concentration to an area
of high concentration (against the concentration gradient)
It requires energy from cellular respiration, because the active transport system has to carry
a molecule across the membrane, and then return…

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Insects have an internal respiratory system, supplying oxygen directly to the cells
Insects have spiracles that open when the insect needs oxygen, and these lead to the
tracheoles,
The tracheoles are minute breathing tubes which penetrate right through the tissues- they
have a large surface area, moist lining, air is…

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Red blood cell adaptations for efficiency in picking up oxygen:
They are biconcave discs, giving them an increased surface area: volume ratio
Packed full of haemoglobin, which carries oxygen
No nucleus, so more space to pack haemoglobin
Haemoglobin reacts to form oxyhaemoglobin with oxygen, and where oxygen concentration
is lower,…

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Dialysis machine carries out the functions of the kidney
Person's blood leaves body and flow between partially permeable membranes
Other side of membranes is dialysis fluid, and the concentration of this fluid means that
unwanted substances in the blood pass into the fluid (urea, excess ions and water)
Dialysis fluid…

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Bacteria break down lactose in the milk to produce lactic acid- this is called lactic
fermentation
Lactic acid causes milk to clot and solidify into yoghurt
Yoghurt-forming bacteria help to prevent the growth of bacteria which make milk go
off
To make cheese:
Add a starter culture of bacteria to…

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Cost- continuous generators are more expensive
Convenience- batch generators are less convenient
Efficiency- need to be well insulated and no leaks
Position- away form homes
Many different organisms are involved in the breakdown of material in biogas production
Sugar cane contains sucrose (high in carbohydrates) and maize contains starch which…

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