Transport around the body

Revision notes based on transport around the body for both simple and multicellular organisms (Edexcel AS Biology) :') 

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Transport around the body
Transport in simple organisms
One main way substances move in and out of cells is by diffusion
Diffusion: the movement of particles in a liquid or a gas down a concentration gradient from an
area where they are at a relatively high concentration to an area where they are at a relatively
low concentration.
For unicellular organisms such as Amoeba, nutrients and oxygen can diffuse directly into the cell from its
external environment, and waste substances can diffuse directly out. This is because the surface area ­
to ­ volume ratio of the Amoeba is large and because the organism is just one cell, substances do not
need to travel from cell to cell inside it.
Transport in large organisms
Large organisms are made up of billions of cells and are often organised into specialised tissues and
organs. Substances need to travel long distances from the outside to reach the cytoplasm of the cells.
Nutrients and oxygen would eventually reach the inner cells by simple diffusion but not fast enough to
sustain life.
Complex organisms have evolved specialised systems to get food and oxygen into their bodies
In humans these systems are the gut and lungs and to remove waste (gut, lungs, skin and
kidneys)
They also carry internal transport systems which carries substances to every cell in the body,
delivering oxygen and nutrients and taking away waste quickly so that cells can carry their
reactions efficiently
In large complex organisms (e.g. humans) chemicals made in a cell in one part of the body e.g. a
hormone such as insulin or adrenaline- may have an effect on a different part of the body
In humans this transport system is the heart and the circulatory system and the blood which flows
through it. This is an example of a mass transport system (substances are transported in the flow of a
fluid with a mechanism for moving it around the body)
Substances are delivered over short distances by: diffusion, osmosis (the movement of water
along a concentration gradient though a partially permeable membrane) and active transport (in
which energy is required to move substances against a concentration gradient)
Features of a mass transport system
Mass transport system makes an effective transport system Most have certain features in common:

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A system of vessels that carry substances: these are usually tubes, sometimes following a very
specific route, sometimes widespread and branching
A way of making sure that substances are moved in the right direction e.g.…read more

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