The circulatory system
The need for transport systems
In single-celled organisms such as A group of small organisms that are not animals, plants or fungi but share some of their characteristics., and small Having more than one cell. organisms, essential A collection of two or more atoms held together by chemical bonds. will move to where they're needed by The movement of molecules from an area of higher concentration to an area of lower concentration..
Once an Living entity, eg animals, plants or microorganisms., eg a very early An organism in the early stages of development., gets beyond a certain size, it needs a transport system to distribute essential molecules efficiently.
Features of transport systems
Common features of transport systems:
- they are made up of tubes or 'vessels' that carry materials from one part of the organism to another
- they make close contact with cells, such as those of exchange surfaces
What substances are transported in the blood?
| Substance transported | From | To |
| Oxygen | The lungs | All the body's cells |
| Carbon dioxide | All the body's cells | Lungs |
| Glucose | Digestive system | The liver, then all the body's cells |
| Urea | Liver cells | Kidneys |
| Substance transported | Oxygen |
|---|---|
| From | The lungs |
| To | All the body's cells |
| Substance transported | Carbon dioxide |
|---|---|
| From | All the body's cells |
| To | Lungs |
| Substance transported | Glucose |
|---|---|
| From | Digestive system |
| To | The liver, then all the body's cells |
| Substance transported | Urea |
|---|---|
| From | Liver cells |
| To | Kidneys |
Other substances transported in the blood include:
- A protein produced by the immune system in humans (and other animals) that attacks foreign organisms (antigens) that get into the body.
- Chemical messenger produced in glands and carried by the blood to specific organs in the body.
Oxygen is carried in The blood cell which contains the pigment haemoglobin responsible for the transport of oxygen.. Dissolved substances are carried in the The liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea..