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In single-celled organisms, how is everything they need to import and export supplied?
By processes such as diffusion, osmosis, active transport, endocytosis and exocytosis, which are also important in multicellular organisms.
As organisms get bigger, what also increases?
The distance between the cells and the outside of the body.
In multicellular organisms, what would diffusion transport?
Substances into and out of the inner core of the body, but it would be so slow that the organism would not survive.
Why are specialised transport systems needed?
To meet the high metabolic demands of multicellular organisms.
The SA:V ratio is small.
Molecules such as hormones or enzymes may 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 to use for respiration and other aspects of cell metabolism.
Waste products of metabolism need to be removed from the cells and transported to excretory organs
What does it mean if an organism has a high metabolic demand?
It needs lots of oxygen and food, and produces lots of waste products.
What does a small SA:V ratio mean?
The amount of surface area available to absorb or remove substances is small.
What do most large, multicellular organisms have?
Specialised circulatory (transport) systems.
What do specialised circulatory systems carry?
Gases such as oxygen and carbon dioxide, nutrients, waste products and hormones around the body.
What features do most circulatory systems have in common?
A liquid transport medium that circulates around the system - blood.
Vessels that carry the transport medium.
A pumping mechanism to move the fluid around the system.
What are mass transport systems?
When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body.
What type of transport systems do large, multicellular organisms usually have?
Either an open circulatory system or a closed circulatory system.
What is an open circulatory system?
One where there are very few vessels to contain the transport medium. It is pumped straight from the heart into the body cavity of the animal.
In an open circulatory system, what is the open body cavity of the animal called?
Haemocel.
What happens in the haemocoel?
The transport medium is under low pressure. It comes into direct contact with the tissues and the cells: this is where exchange takes place between the transport medium and the cells.
In an open-ended circulatory system, how does the transport medium return to the heart?
Through an open ended vessel.
Where are open ended circulatory systems mainly found?
in invertebrate animals, including most insects and some molluscs.
In insects, where does gas exchange take place?
In the tracheal system.
What is insect blood called?
Haemolymph; it dosen’t carry oxygen or carbon dioxide, it transports food and nitrogenous waste products and the cells involved in defense against disease.
In insects, what is the body cavity split by?
A membrane and the heart extends along the length of the thorax and the abdomen of the insect.
Does the haemolymph circulate?
Yes, but steep diffusion gradients cannot be maintained for efficient diffusion: The amount of haemolymph flowing to a particular tissue cannot be varied to meet changing demands.
What is a closed circulatory system?
One where the blood is enclosed in blood vessels and does not come into direct contact with the cells of the body. the heart pumps blood around the body under pressure and relatively quickly, and the blood returns to the heart.
In a closed circulatory system, how do subtances leave and enter the blood?
By diffusion thriugh the walls of the blood cells.
In a closed circulatory system, how is the amount of blood flowing to a particular tissue adjusted?
By the widening or narrowing of blood vessels.
Where are closed circulatory systems found?
Many different animal phyla, including fish and annelid worms.
What happens in single closed circulatory systems?
The blood flows through the heart and is pumped out to travel all around the body before returning to the heart. The blood travels only once through the heart for each complete circulation of the body.
What happens in single closed circulation?
The blood passes through two sets of capillaries before it returns to the heart. In the first set of capillaries, carbon dioxide and oxygen are exchanged, in the second, substances are exchanged between the blood and the cells.
What happens as a result of blood passing through two sets of capillaries?
The blood pressure in the system drops considerably so the blood returns to the heart quite slowly, limiting the efficiency of the exchange process so the activity levels of animals with single closed circulations tend to be very low.
Which animal are the exceptiont to animals that use a closed circulatory system having low activity?
Fish.
Why are fish the exception to animals that use a closed circulatory system having low activity?
They have a relatively efficient single circulatory system, which means they can be very active.
What kind of gaseous exchange mechanism do fish have?
A countercurrent one - their gills allow them to take a lot of oxygen from the water.
Their body weight is supported by the water.
They do maintain their own body temperature, greatly reducing the metabolic demads on their bodies - combined with their efficient gas exchange, explains how fish are able to be active with a single closed circulatory system.
What are birds and most mammals?
Very active land animals that maiintain their own body temperature.
How are birds and most mammals able to maintain their own body temperature?
Because of their double closed circulatory system - it is the most efficient system for transporting substances around the body.
How many circulations does a double closed circulatory system invole?
Two seperate ones.
What are the two circulations in the double closed circulatory system?
Blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide, amd then returns to the heart.
Blood flows through the heart and is pumped out to travel around the body before returning to the heart again.
Why is it that a relatively high pressure and fast flow of blood can be maintained in a double circulatory system?
The blood travels twice through the heart for each circuit of the body. Each circuit only passes through one capillary network.
