The need for transport systems
In single-celled organisms such as A eukaryotic, usually single-celled organism of the kingdom Protista., 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. – for instance a very early An organism in the early stages of development. – or species of organism 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 | Lungs | All cells in the body |
| Carbon dioxide | All cells in the body | Lungs |
| Glucose | Digestive system | Liver, then the rest of the cells in the body |
| Urea | Liver | Kidneys |
| Substance transported | Oxygen |
|---|---|
| From | Lungs |
| To | All cells in the body |
| Substance transported | Carbon dioxide |
|---|---|
| From | All cells in the body |
| To | Lungs |
| Substance transported | Glucose |
|---|---|
| From | Digestive system |
| To | Liver, then the rest of the cells in the body |
| Substance transported | Urea |
|---|---|
| From | Liver |
| 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 within red blood cells. 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..
The need for exchange surfaces
Living entity, eg animals, plants or microorganisms. must take in food, Gaseous element making up about 20% of the air, which is needed by living organisms for respiration. and water, and other essential substances, from the environment. Plants also need A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis. for A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic.. Organisms also need to remove waste substances.
Small organisms exchange these essential and waste substances between themselves and the environment. They do this over their body surface. Simple chemical substances can When particles spread out from a region of higher concentration to a region of lower concentration. in and out of their bodies.
Inside their bodies, in small organisms, substances don't have to move far.
The size of their surface, or surface area, defines how quickly they can absorb substances.
The size of their volume defines how much of these substances they need.
Modelling cells
If we represent the cell of an organism by a cube:
This is what happens when the cube increases in size:
As the volume increases, surface area does not increase at the same rate.
As multicellular organisms increase in size, they therefore face two problems
| Problem | Solution | |
| Their surface area does not increase as fast as the volume | Insufficient surface area to meet their needs | Body systems that add additional absorbing area to exchange surfaces |
| Their volume increases | Diffusion is not quick enough to move substances to where they're needed in the organism's body | A transport system |
| Their surface area does not increase as fast as the volume | |
| Problem | Insufficient surface area to meet their needs |
| Solution | Body systems that add additional absorbing area to exchange surfaces |
| Their volume increases | |
| Problem | Diffusion is not quick enough to move substances to where they're needed in the organism's body |
| Solution | A transport system |
