Section 3 - Exchange Flashcards
How do cells survive?
The external environment is different from the internal environment found within an organism and within its cells. Organisms transfer materials between the two environments. This takes place at exchange surfaces.
Where does cellular exchanges take place?
Takes place at exchange surfaces Always involves crossing cell plasma membranes.
What is always involved in cellular exchange?
Crossing cell plasma membranes.
Why is it essential to have a large surface area to volume ratio?
Speeds up the rate of diffusion
Why is it essential to have a thin exchange surface?
It keeps the diffusion pathway short
Why are partially permeable membranes good in exchange surfaces?
To allow selected materials to diffuse
List the parts of the gas exchange system of terrestrial insects in the order that oxygen passes from outside the body to the respiratory tissues.
- Spiricals - Trache - Tracheoles - Air sacs
State two ways in which insects ventilate their exchange systems
- Abdominal movement - Muscle contracting - Spircle opening and closing
Explain the mechanism by which insect respiratory systems respond to oxygen debt during high intensity exercise
The tracheole ends are filled with water. Lactate builds up around the muscles. Lactic acid is soluble. Increasing water potential. This means water is drawn into the cell. This gives more space for more oxygen to be available. This extends the reach of air into the tissues as there is less water in the tracheole ends.
Explain why there is a conflict in terrestrial insects between gas exchange and water conservation
If you want to do gas exchange you need to open the spiricles however this increases the amount of mostiture lost.
What is a hypotonic solution?
Any solution that has a lower osmotic pressure than another solution.
What is a hypertonic solution?
Greater concentration of solutes on the outside of a cell when compared with the inside of a cell
What is water potential?
Water potential is the ‘measure of the ability of water molecules to move freely in solution’. All this means is that is a solution of pure water where there is no solute, all of the water molecules are free to move, so the water potential is high
Explain how the tracheal system limits the size of insects
if insects were bigger than the diffusion pathway should be longer which would make it inefficient for diffusing oxygen. They would also then lose a lot more moisture.
Explain the difference between parallel and counter current
In countercurrent all of the oxygen is absorbed where as in parallel only 50% of the oxygen from the water diffuses into the blood.
What is always involved in the transfer of materials between the external and internal environment?
A cells plasma membrane is always crossed
What is the name given for the environment around the cells of multicellular organisms?
Tissue fluid
What is the mass transport system involved in? What is the role in this process?
The movement of tissue fluid to keep its composition constant. It distributes to the tissue fluid and waste products returned to exchange surface for removal. Maintaining the diffusion gradients that bring materials to and from the cell-surface membranes.
What are 4 things that need to be interchanged between an organism and its environment?
Respiratory gases
Nutrients
Excretory products
Heat
What are the respiratory gases?
Oxygen Carbon dioxide
What must the organism need in order to make the exchange effective?
The exchange surface of the organism must be large compared to its volume.
Equation - Surface area of cube
area of one side x 6
Equation - volume
length x height x width
What adaptions have made larger organisms more efficient?
A flattened shape so that no cell is ever far from the surface A specialised exchange surface with large areas to increase the surface area to volume ratio.
Equation - Volume of a sphere
4/3 pi r^3
What characterises do exchange surfaces show to make them efficient ?
Large surface area relative to the volume of the organism which increases the rate of exchange Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly. Selectively permeable to allow selected materials to cross. Movement of environmental medium eg. air to maintain diffusion gradient Transport system to ensure the movement of the internal medium eg. blood in order to maintain a diffusion gradient.
Why does this adaptation make an exchange surface more efficient? Large surface area relative to the volume of the organism
Increases rate of exchange
Why does this adaptation make an exchange surface more efficient? Very thin
diffusion distance is short and therefore materials cross the exchange surface rapidly
Why does this adaptation make an exchange surface more efficient? Selectively permeable
allow selected materials to cross.
Why does this adaptation make an exchange surface more efficient? Movement of environmental medium
maintain diffusion gradient
Why does this adaptation make an exchange surface more efficient? Transport system to ensure the movement of the internal medium
maintain diffusion gradient
How can you express the relationship between Surface area Length of the diffusion path Diffusion Difference in concentration
Diffusion = SA x Difference in conc. / length of diffusion path
How does an increased surface area in terrestrial insects effect water conservation?
Conflicts with it as water will evaporate more from a large SA
what is the tracheae in terrestrial insects?
Internal network of tubes Supported by strengthened rings to prevent them from collapsing.
What are the tracheoles in terrestrial insects?
Divisions of tracheae They extend throughout all the body tissues of the insect. Oxygen brought directly to respiring tissues as there is a short diffusion pathway from tracheole to any body cell.
State the three ways gases move in and out of the tracheal system.
Along a diffusion gradient Mass transport The ends of the tracheoles are filled with water
Why does gases move along a diffusion gradient in and out of a tracheal system?
When respiring, oxygen is used up so concentration falls. This creates a diffusion gradient causing gaseous oxygen to diffuse
Explain the movement of oxygen through a tracheal system
A diffusion gradient caused gaseous oxygen to diffuse from the atmosphere along the tracheae and tracheoles to the cells. Carbon dioxide is produced during respiration. This creates diffusion gradient in the opposite direction. This causes gaseous carbon dioxide to diffuse along the tracheoles and tracheae from the cells to the atmosphere.
Why are respiratory gases exchanged quickly by the process of diffusion?
As diffusion in the air is more rapid than diffusion in water.
Explain how respiratory gases move in and out of the tracheal system by mass transport
The concentration of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases.
What happens to the tracheoles during periods of major activity in terrestrial animals?
During periods of major activity, the muscle cells around the tracheoles respire carry out out come anaerobic respiration. This produces lactate
What is lactate?
Soluble and lowers the water potential of muscle cells around the tracheoles.
What process means that water can move into muscle cells around the tracheoles?
Osmosis
What happens when water goes through osmosis and draws water into muscle cells around the tracheoles?
Water in the ends of the tracheoles decrease in volume and in doing so they draw air further into them. This means the the final diffusion pathway is in a gas rather than a liquid phase, and therefore diffusion is more rapid. This increases the rate at which air is moved in the tracheoles but leads to greater water evaporation.
What are spiracles?
Tiny pores that mean gases can enter and leave tracheae.
How do spiracles open and close?
A valve
What happens when spiracles are open?
Water vapour can evaporate from the insect.
Why do insects normally keep their spiracles closed?
Prevent water loss
Why do spiracles open?
To allow gas exchange.
What are the limitations of the tracheal system?
- Relies mostly on diffusion to exchange gases between the environment and the cells. - Diffusion pathway limits the size that insects can attain.
Why are insects such a small size?
To be effective, the diffusion pathway needs to be short so they need to be small.
Explain the structure of a fishes outer covering
Waterproof and therefore gas-tight.
As fish are relatively large what does this mean for their SA:V?
Small surface area to volume ratio. So body surface not adequate to supply and remove their respiratory gases and so they have evolved a specialised internal gas exchange.
What specialised internal gas exchange system do fish use?
The gills
Where are the gills located?
Within the body of the fish behind the head.
What are the gills made up of?
Gill filaments
What is the structure of gill filaments?
Gill filaments are stacked up in a pile like pages of a book. At right angle to the filaments are fill lamellae.
What is the role of gill lamellae?
Increase the surface area of the gills
Where is the gill lamellae found?
At right angle to the gill filament.
Explain the water movement in fish?
Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body.
What is countercurrent flow?
The flow of water over the gill lamellae and flow of blood within them are in opposite directions.
Why is the countercurrent flow in fish gills important?
To ensure the maximum possible gas exchange is achieved within the fishes gills
What is the essential feature of the countercurrent exchange system?
The blood and the water that flow over the gill lamellae do so in opposite directions.
What does the arrangement of the countercurrent flow mean?
- Blood that is already well loaded with oxygen meets water which has its maximum concentration of oxygen. Therefore diffusion of oxygen from the water to the blood takes place. - Blood with little oxygen in it meets water which has had most, but not all, of its oxygen removed. Again, diffusion of oxygen from the water to blood takes place.
What proportion of all the available oxygen in the water is absorbed by countercurrent flow in fish gills?
80%
Define - parallel flow
The flow of water and blood had been in the same direction.
In parallel flow what proportion of available oxygen would be absorbed by the blood?
50%
Why is the oxygen absorption in parallel flow so low?
The diffusion gradient would only be maintained across part of the length of the gill lamellae. Only 50%
Explain the diffusion of oxygen due to the countercurrent flow
A diffusion gradient is maintains all the way across the gill lamellae. Almost all the oxygen from the water diffuses into the blood
What is the diffusion of oxygen like in a parallel flow system?
A diffusion gradient is maintained for only half of the distance across the gill lamellae. Only 50% of the oxygen from the water diffuses into the blood.
What processes do plants use in gaseous exchange?
Respiration and photosynthesis
What can reduce gas exchange with the external air in leaves?
Gases produced in either respiration or photosynthesis can be used for the other.
Where is carbon dioxide found for photosynthesis to occur in plants?
Some from respiration off cells but most from the external air.
