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Exchange and Transport

For exchange to be effective:

The surface area of an organism must be large compared with its volume.
Thin exchange surface to give a short diffusion pathway
Partially permeable to allow selected materials to cross
Movement of the environmental medium (e.g. air)
Movement of the internal medium…

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Gas exchange in fish

Fish have developed a specialised internal gas exchange surface (gills) because their waterproof
covering and small surface area to volume ratio means their body surface is not adequate to
supply and remove their respiratory gases via diffusion.

Gills are
located behind
the heads of
fish and…

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Circulatory system of a mammal

Features of transport systems:

A suitable medium in which to carry materials (e.g. blood)
A form of mass transport in which the transport medium is moved around in bulk
A cosed system of tubular vessels that contains the transport medium and forms a
branching network…

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bathes all the cells of the body. It provides a mostly constant environment for the cells it

Blood is pumped along arteries, into narrower arterioles and then narrower capillaries, creating
hydrostatic pressure at the arterial end of the capillaries. This pressure forces tissue fluid out of
the blood plasma…

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Epidermis ­ a single layer of cells often with long extentions called root hairs which
increase the surface area. A single plant may have 1010 root
Cortex ­ a thick layer of packing cells often containing stored
Endodermis ­ a single layer of cells that surround the vascular…

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The uptake of water by osmosis actually produces a force that pushes water up the xylem. This
force is called root pressure which can be measured by placing a manometer over a cut stem. This
force helps push water up short stems i.e. a few centimetres however longer distances like…

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Factors affecting transpiration

Temperature ­ high temperature increases the rate of evaporation of water from the surface of
the spongy mesophyll cells because it increases the kinetic energy of the water molecules. This
raises the in the sub-stomatal air space and means that the molecules are moving faster so

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Hydrophytes ­ adapted to freshwater habitat
Mesophytes ­ adapted to habitat with adequate water

Adaptations of xerophytes:

Adaptation How it works Example
Thick waxy cuticle Stops uncontrolled Conifer needles
evaporation through palisade
Small leaf surface area Less area for evaporation Conifer needles
Low stomata density Fewer gaps for water…


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