Exchange and Transport Systems Flashcards
Give examples of things which need to be interchanged between an organism and its environment.
- Respiratory gases (oxygen and carbon dioxide)
- Nutrients (glucose, fatty acids, amino acids etc).
- Excretory products (urea and carbon dioxide).
What are the two ways exchange can take place?
Passively (no energy is required), by diffusion and osmosis.
Actively (energy is required), by active transport.
For gas exchange to be effective, the surface area must be…
large compared with its volume.
To overcome the problem larger organisms have of having a larger volume to surface area ratio they often evolved to have…
- a flattened shape so that no cell is ever far from the surface.
- specialised exchange surfaces with large areas to increase the surface area to volume ratio (e.g. lungs in mammals, gills in fish).
What characteristics do specialised exchange surfaces have?
- A large surface area to volume ration to increase the rate of exchange.
- Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly.
- Partially permeable to allow selected materials to cross without obstruction.
- Movement of the environmental medium to maintain a diffusion gradient.
- Movement of the internal medium to maintain a diffusion gradient.
Diffusion =
surface area x difference in concentration / length of diffusion path.
How does gas exchange occur in single celled organisms?
They are small with a large surface area to volume ratio.
Oxygen is absorbed by diffusion across their body surface, which is covered only by a cell surface membrane.
What is the problem for all terrestrial organisms?
Water easily evaporates from the surface of their bodies and they can become dehydrated.
They therefore need to conserve water.
What is the conflict for terrestrial organisms?
Between efficient gas exchange and a need to conserve water.
To reduce water loss, terrestrial organisms usually exhibit what two features?
- Waterproof coverings- over their body surfaces. In the case of insects this covering is a rigid outer skeleton that is covered with a waterproof cuticle.
- Small surface area to volume ratio to minimise the area of which water is lost.
How does gas exchange occur in insects?
They have developed an internal network of tubes called tracheae which are supported by strengthened rings to prevent them from collapsing. The trachea divide into smaller tubes called tracheoles..
In multicellular organisms, diffusion across the outer membrane is too slow, for what too reasons?
Some cells are deep within the body- there’s a big distance between them and the outside environment.
Large animals have a low surface area to volume ratio- it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.
What does ‘mass transport’ refer to in mammals?
The circulatory system, which uses blood to carry glucose and oxygen around the body. It also carries hormones, antibodies and waste like CO2.
Do most large animals have a higher or lower surface area to volume than small animals?
Lower
Give two reasons why diffusion is slow in multicellular organisms for them to absorb and excrete substances this way.
Some cells are deep within the body so the distance between them and the outside environment is too great for diffusion to take place quickly.
Larger animals have a low surface area to volume ratio meaning they don’t have a large enough area exposed to the environment to be able to exchange all the substances they need quickly enough using diffusion.
