8.1 Transport Systems in Multicellular Animals Flashcards
Why do multicellular animals need specialised transport systems?
High metabolic demands so diffusion over long distance is not enough to supply quantities needed
Surface area to volume ratio is small
Molecules ( eg hormones , enzymes ) may be made in one place but needed in another
Food digested in one organ system, but needs to be transported to every cell for use in respiration and other aspects of cell metabolism
Waste products of metabolism need to be removed from the cells and transported to excretory organs
Define mass transport
When substances are transported in a mass of fluid
Describe open circulatory systems
Very few vessels to contain transport medium
Pumped straight from heart into body cavity (haemocoel) of animal
Comes into direct contact with tissues and cells
Describe the circulatory system of insects
Open
Insect blood (haemolymph) transports food and nitrogenous water products and immune system cells
Body cavity is split by membrane
Heart extends along the length of the thorax and abdomen
What are the disadvantages of open circulatory systems?
Steep diffusion gradients cannot be maintained for efficient diffusion
Amount of blood flowing to a particular tissue cannot be varied to meet changing demands
Describe closed circulatory systems
Blood is enclosed in blood vessels
Doesn’t come into contact with cells of the body
Heart pumps blood around the body under pressure and relatively quickly
Substances leave and enter the blood by diffusion
What are the advantages of closed circulatory systems
Amount of blood flowing to a particular tissue can be adjusted by widening or narrowing blood vessels
Blood transported under pressure so it is fast and efficient
Describe single circulatory systems
The blood flows through the heart once
The blood passes through two sets of capillaries before it returns to the heart
What are the disadvantages of single circulatory systems ?
As it passes through two sets of narrow vessels the blood pressure drops so blood returns to the heart slowly
Describe double circulatory systems
Blood travels twice through the heart
Once to the lungs and once to the body
What is the advantage of double circulatory systems ?
Each circuit only travels through one capillary network, which means a high pressure and fast flow of blood can be maintained
