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transport systems in multicellular animals (need for specialised transport…
transport systems in multicellular animals
need for specialised transport systems
high metabolic demands
diffusion over long distances not enough to supply quantities needed
small SA:V ratio
amount of surface area available to absorb or remove substances is small
hormones or enzymes made in one area but needed in another
food digested in one organ system but needs transporting to every cell for respiration and cell metabolism
waste products of metabolism need removing from cells and transported to excretory organs
features of a circulatory system
liquid transport medium that circulates around the system
e.g. blood
vessels that carry transport medium
pumping mechanism to move fluid around system
closed circulatory system
blood enclosed in blood vessels
does not come into contact with cells of the body
usually has blood pigment that carries respiratory gases
heart pumps blood around body under pressure quickly
blood returns directly to heart
substances leave and enter blood by diffusion through blood vessel walls
amount of blood flowing to a particular tissue can be adjusted
widening or narrowing blood vessels
found in many animals e.g. sea urchins, starfish and all vertebrates
open circulatory system
few vessels to contain transport medium
transport medium pumped straight from heart to body cavity of animal
open body cavity - haemocoel
transport medium under low pressure here
returns to heart through open ended vessel
comes into contact with tissues and cells
where exchange takes place between transport medium and cells
body cavity split by membrane
heart extends along length of thorax and abdomen
mainly found in invertebrate animals e.g. insects, molluscs
insect blood - haemolymph
transports food and nitrogenous waste products - no oxygen or carbon dioxide
haemolymph circulates - steep diffusion gradients cannot be maintained
cannot vary amounts of haemolymph flowing to particular tissues to meet different demands
single closed circulatory systems
e.g. fish, worms
blood flows through heart and pumped through body before returning to heart
blood travels only once through heart for each complete circulation of body
blood passes through two sets of capillaries before returning to heart
first set of capillaries
exchanges oxygen and carbon dioxide
second set of capillaries
substances exchanged between blood and cells
passing through very narrow vessels
blood pressure drops considerably
blood returns to heart quite slowly
limits efficiency of exchange processes
animals with single closed circulations have low activity levels
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double closed circulatory systems
birds and most mammals are very active land animals
maintain their own body temperature
way of life made possible by double closed circulatory system
most efficient system for transporting substances around the body
two separate circulations
blood pumped from heart to lungs to pick up oxygen and unload carbon dioxide then returns to heart
blood flows through heart and is pumped out to travel around the body before returning to heart again
blood travels twice through the heart for each circuit of the body
each circuit only passes through one capillary network
relatively high pressure maintained
fast flow of blood