8.1 Transport In Multicellular Animals Flashcards
Why do multicellular organisms need specialised transport systems?
Metabolic demands of multicellular animals are high and diffusion over large distances cannot meet this demand
SA:V ratio gets smaller as organism gets larger, so larger diffusion distances and slower rate of diffusion
Molecules (eg-hormones and enzymes) can be made in one place but needed in another
Food will be digested in one organ system but needs to be transported to every cell
Waste products of metabolism need to be removed from cells and transported to excretory organs
Common features of most circulatory systems
They have a liquid transport medium that circulates around the system (blood)
They have vessels to transport the medium
Pumping mechanism to move fluid around
What is a mass transport system?
When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body
Open circulatory system
Where there are few vessels to contain the transport medium
How is blood transported in an open circulatory system?
Pumped straight from the heart to the haemocoel
In the haemocoel, the transport medium is under low pressure
Comes into direct contact with tissues and cells, where exchange takes place
Returns to the heart via an open ended vessel
What is a haemocoel?
Open body cavity
Which organisms have open circulatory systems?
Invertebrate animals (most insects) and molluscs
What is insect blood called?
Haemolymph
What does haemolymph carry?
Food and nitrogenous waste products
Cells involved in disease defence
Where is the heart of an insect found?
Along the thorax and the abdomen of the insect
Disadvantages of open circulatory system
Steep diffusion gradients cannot be maintained for efficient diffusion
Amount of haemolymph flowing to a certain area cannot be varied depending on demand
Closed circulatory system
Blood is enclosed within blood vessels and doesn’t come directly in contact with cells of the body
How does a closed circulatory system work?
Heart pumps blood around the body under pressure and relatively quickly, returns to heart
Substances leave and enter the blood by diffusion through the walls of the blood vessels
Advantages of closed circulatory system
Amount of blood flowing to a particular tissue can be adjusted by widening/narrowing blood vessels
Single circulatory system
Blood flows through the heart only once for each complete circulation of the body
