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.
What is meant by a mass transport system?
A system in a multicellular organism that carries substances to and from individual cells.
Will the rate of heat loss at a given temperature be greater for an animal with a high or low surface area:volume ratio?
High surface area: volume ratio
Explain how an animal’s shape can help to control its temperature?
An animal with a compact shape has a low surface area: volume ratio. This means they lose less heat an animal with a less compact shape has a higher surface area: volume ratio. This means they lose heat more easily.
Other than body size or shape, give two adaptations a small animal may have to survive in a cold environment?
They might have a higher metabolic rate, might hibernate, thick layers of fur.
Other than body size or shape, give two adaptations a large animal may have to survive in a hot environment?
Spend a lot of time in water, features that increase surface area e.g large ears.
What is a gas exchange surface?
A boundary between the outside environment and the internal environment of an organism.
What do most gas exchange surfaces have in common?
A large surface area.
They’re thin- provides a short diffusion pathway across the gas exchange surface.
The organism also maintains a steep concentration gradient of gases across the exchange surface, which increases the rate of diffusion.
How is gas exchanged in single celled organisms?
Single celled organisms absorb and release gases by diffusion through their outer surface.
They have a relatively large surface area, a thin surface and a short diffusion pathway so theres no need for a gas exchange system.
What is the gas exchange system in fish?
The gills.
What is the structure of the gills?
Water containing oxygen enters through fish mouth and passes out through gills.
Each gill is made of lots of thin plates called gill filaments which give a large surface area for gas exchange.
These area covered in lamellae which increase the surface area even more.
These have lots of blood capillaries and a thin surface layer of cells to speed up diffusion, between the water and the blood.
What is the counter current system?
In the gills of a fish, blood flows through the lamellae in one direction and water in the opposite.
This counter current system means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen.
Steep concentration gradient is maintained.
How does gas exchange in dicotyledonous plants work?
Plants need CO2 for photosynthesis, which produces O2 as a waste gas.
They need O2 for respiration, which produces CO2 as a waste gas.
The main gas exchange surface is the mesophyll cells in the leaf which has a large surface area.
Gases move in and out through pores in the epidermis called stomata which can close to stop water loss.
Guard cells control the opening/closing.
How does gas exchange in insects work?
Air moves into the trachea through pores on the surface called spiracles.
Oxygen travels down the conc gradient towards the cells.
CO2 from the cells moves down its own conc gradient towards the spiracles to be released into the atmosphere.
The trachea branch off into smaller tracheoles which have thin, permeable walls and go to individual cells.
Oxygen therefore diffuses directly into the respiring cells- the insects circulatory system doesn’t transport O2.
How is air moved in and out of spiracles of insects?
Rhythmic abdominal movements to more air in and out of the spiracles.
What do insects do if they’re losing too much water?
They close their spiracles using muscles.
They also have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduces evaporation.
How are plants adapted to deal with water loss?
Plants’ stomata are usually kept open during the day to allow gaseous exchange.
Water enters the guard cells, making them turgid, which opens the stomatal pore.
If the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore.
What is a xerophyte?
Plants that are specially adapted for life in warm, dry of windy habitats, where water loss if a problem.
What are some xerophytic adaptations?
- Stomata sunk in pits to trap water vapour, reducing evaporation by lowering the conc gradient.
- Curled leaves with the stomata inside, protecting them from wind and so reducing water loss.
- A later of ‘hairs’ on the epidermis to trap water vapour round the stomata, reducing the diffusion gradient.
- Reduced number of stomata, so fewer places for water to escape.
- Waxy, waterproof cuticles on leaves and stems to reduce evaporation.
