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EXCHANGE AND TRANSPORT
Once substances are absorbed, the materials need to be rapidly distributed all
around the body because cells need them and the waste products are returned to
the exchange surface for removal. Therefore a transport system is
necessary.

The size and the metabolic rate of an organism will…

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· Partially permeable to allow selected material to cross through without
obstruction
· Movement of environment medium e.g. air, diffusion gradient
· Movement of internal medium e.g. blood


surface area*difference in concentration
Diffusion length of diffusion path










Exchange surfaces are often situated inside the organism because they are very
thin…

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Most insects are terrestrial (live on land). Water easily evaporates from the surface
of their bodies and they can easily become dehydrated. Therefore they need to
conserve water.
To reduce water lose, terrestrial organisms has:-

Waterproof covering- this covering is rigid and when water evaporates
the water proof layer doesn't…

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Respiratory gases move in and out in two ways:-

Along a diffusion gradient- oxygen is used up when
cells are respiring, so concentration of oxygen decreases towards the end
of the tracheoles and creates a diffusion gradient that causes the oxygen
from atmosphere to diffuse into tracheae and then tracheoles.…

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in opposite direction. This is known as COUNTER
CURRENT FLOW. If blood flow in the same direction as water, then
far less gas exchange would take place.




THE COUNTER CURRENT EXCHANGE
The blood and the water that flow over the gill lamellae in opposite directions,
this arrangement means that:

Blood…

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CIRCULATORY SYSTEM OF A MAMMAL
The efficient supply of materials over larger distances requires a mass transport
system.

Transport system depends on:-
The surface area to volume ratio
How active the organism is

The lower the surface area to volume ratio and the more active
the organism, the greater is…

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A mechanism for moving the transport medium within the
vessels. This requires a pressure difference b/w one part of the system and
another. this is achieved in two ways:-
Animals use muscular contraction or special ump like heart
Pants use passive natural physical processes such as the evaporation of
water…

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GAS EXCHANGE IN THE LEAF
The volume and types of gases that are being exchanged by a plant leaf depends
on the balance between the rates of photosynthesis and
respiration.

When photosynthesis is taking place some CO2 from respiration is used and
some from external air. In the same way…

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