3.1.2 a and b transport systems in multicellular animals Flashcards
why are specialised transport systems needed?
metabolic demands of animals are high and diffusion over long distances isn’t enough to supply the quantities needed.
surface area to volume ratio gets smaller as the animal gets bigger so surface area available to absorb or remove substances becomes smaller.
hormones or enzymes might be made in one place and needed in another.
food will be digested in one organ system but needs to be transported to every cell for respiration.
waste products need to be removed.
what do circulatory systems do?
carry oxygen. carbon dioxide, nutrients, waste products, hormones around the body
features of a circulatory system
liquid transport medium that circulates around the system.
vessels to carry the transport medium.
pumping mechanism to move fluid around the system.
what is a mass transport system?
substances that are transported in a mass of fluid with a mechanism for moving the fluid around the body
what is an open circulatory system?
a circulatory system with very few vessels to contain the transport medium
what is the open body cavity called?
haemocoel
what is insect blood called?
haemolymph
what does the haemolymph do?
transport food, nitrogenous waste and the cells that are involved in defence against disease
how does the open circulatory system work in an insect?
haemocoel is under low pressure.
it comes into contact with the tissues and cells.
this is where exchange takes place.
transport medium returns to the heart through an open ended vessel.
body cavity is split by a membrane and the heart extends along the length of the thorax and abdomen of the insect.
haemolymph circulates but a steep diffusion gradient can’t be maintained.
disadvantage of open circulatory system
the amount of haemolymph flowing to a tissue can’t be varied to meet changing demands
what is a closed circulatory system?
blood is enclosed in blood vessels and does not come directly into contact with cells of the body.
how does a closed circulatory system work?
heart pumps blood around the body under pressure and quickly.
blood returns to the heart.
substances leave and enter the blood by diffusion through the walls of the blood vessels.
amount of blood flowing to a particular tissue can be adjusted by narrowing or widening blood vessels.
what is a single closed circulatory system?
the blood flows through the heart and is pumped out to travel all around the body before returning to the heart.
what does the blood pass through in a single closed circulatory system?
two sets of capillaries.
first, it exchanges oxygen and carbon dioxide.
then, substances are exchanged between the blood and the cells.
disadvantages of the single closed circulatory system
because it passes through two sets of very narrow vessels, the blood pressure drops considerably so blood returns to the heart slowly. this limits the efficiency of the exchange processes so the activity levels of animals will be low.
