8.1 Transport systems in multicellular animals Flashcards
what is the need for specialised transport systems
The metabolic demands of most multicellular animals are high so diffusion over the long distances is not enough to supply the quantities needed
The SA:V ratio gets smaller as multicellular organism gets bigger so not only do diffusion distances get bigger but amount of SA available to absorb or remove substances becomes relatively smaller
Molecules such as hormones or enzymes may be made in one place but needed in another
Waste products of metabolism need to be removed from the cells and transported to excretory organs
common features in circulatory systems
they have a liquid transport medium that circulates around the system (blood), have vessels that carry the transport the medium, have a pumping mechanism to move the fluid around the system.
Types of circulatory systems
Open circulatory systems
Closed circulatory system
Single closed circulatory system
Double closed circulatory system
Open circulatory systems
Very few vessels to contain the transport medium
Pumped straight from the heart into the body cavity of the animal (the haemocoel)
In haemocoel transport medium is under low pressure and comes into direct contact with the tissues and cells – where exchange takes place
The transport medium returns to the heart through an open-ended vessel
Closed circulatory systems
Blood is enclosed in blood vessels and doesn’t come into direct contact with any cells
Heart pumps blood around body under pressure and relatively quickly
Substances leave and enter blood through the walls of blood vessels
Single closed circulatory system
Blood travels through the heart once for each complete circulation of the body
Blood passes through two sets of capillaries before returning to the heart
Blood pressure drops after passing through these capillaries so blood returns to heart quite slowly and limits efficiency of the exchange process – activity level of animal is low
double closed circulatory system
Most efficient system for transporting substances around the body
Blood travels through the heart twice for each circuit of the body
Each circuit (to the lungs and to the body) only passes through one capillary network so a relatively high pressure and fast flow of blood is maintained
