Gas Exchange ( 1 ) Flashcards
What is tissue fluid?
Environment around cells of multi cellular organisms
What do all organisms do to survive?
- External environment differs to the internal environment within an organism and its cells.
- All organisms need to transfer materials between the two environment
Where does transfer of materials in an organism take place?
Transfer of materials takes place at exchange surfaces and always involves crossing cell plasma membranes.
Why can most cells not supply or remove tissue fluid?
• Majority of cells are too far from exchange surfaces for diffusion
alone to supply or remove their tissue fluid with the various materials needed to keep its composition constant.
What occurs once materials are absorbed?
- Once absorbed, materials are rapidly distributed to the tissue fluid
- Waste products returned to the exchange surface for removal.
- This involves a mass transport system
Why is the mass transport system needed?
Maintains the the diffusion gradient that brings materials to and from the cell surface membranes.
What affects the amount of material that is exchanged?
- The size and metabolic rate of an organism will affect the amount of each material that is exchanged.
- Organisms with a high metabolic rate exchange more materials and so require a larger surface area to volume ratio.
What are some materials which need to be exchanged?
- Nutrients
- Excretory Products
- Heat
How do these exchanges take place?
- Passively through diffusion or osmosis ( doesn’t require energy )
- Actively, by active transport ( requires energy )
Where does exchange take place?
Exchange takes place at the surface of an organism. but the materials absorbed are used by the cells that mostly make up its volume.
What is required for exchange to be effective?
In order for exchange to be effective, the exchange surfaces of the organism must be large compared with its volume.
What does every organism need to do?
- Supply all cells with substances like glucose and oxygen
* Remove waste products from every cell to avoid damage
How does exchange take place in single celled organisms?
• Substances diffuse directly into/out of the cell across the cell surface membrane.
Why is exchange slow in multi cellular organisms?
- Some cells are too deep within the body, this means there is a large distance between them and the outside environment.
- larger animals have a low surface area to volume ratio, it is difficult to exchange enough substances to supply a large volume through a relatively small outer surface.
What do multi-cellular organisms require, and why?
- Specialised exchange organisms
- Efficient system to carry substances to/from their individual cells ( mass transport ) , because:
- Some cells are too deep within the body, this means there is a large distance between them and the outside environment.
- larger animals have a low surface area to volume ratio, it is difficult to exchange enough substances to supply a large volume through a relatively small outer surface.
