3.3.1 Exchange Flashcards
Where does exchange always occur?
Across cell plasma membranes between two environments
What is tissue fluid?
The environment around the cells of multicellular organisms
Give 4 examples of things that need to be exchanged between an organism and it’s environment.
Respiratory gasses
Nutrients
Excretory products
Heat
Give examples of active and passive exchange.
Active- active transport
Passive- osmosis and diffusion
What is Fick’s law?
Diffusion ~ (surface area * difference in concentration) / length of diffusion pathway
How does metabolic rate effect exchange?
High metabolic rate leads to exchange of more materials
Require larger SA:V ratio
How do organisms evolve to make exchange more efficient?
A flattened shape so that no cell is ever far from the surface
Specialised exchange surfaces with large areas to increase the SA:V ratio
What characterisers are shown by a surface specialised for exchange?
Large SA:V ratio
Thin to reduce diffusion distance
Selectively permeable to allow selected materials across
Movement of environmental medium to maintain diffusion gradient
Transport system to move internal medium to maintain diffusion gradient
Why are specialised exchange surfaces often located inside an organism?
They are specialised to be thin and so would be easily damaged and dehydrated
Describe gas exchange in a single-called organism.
Small= large SA:V ratio
Oxygen absorbed by diffusion across the body surface
Carbon dioxide from respiration diffuses out across their body surface
Cell wall has no effect on diffusion of gasses
How have insects adapted for gas exchange?
Evolved an internal network of tubes called teaches
Trachea are supported by strengthened finds to prevent them from collapsing
Trachea extend into tracheoles
Tracheoles extent to body tissue
Air is brought directly to repairing tissue as there is a short diffusion pathway from a tracheole to any body cell
In which three ways to respiratory gasses move in and out of the tracheal system in insects?
Along a diffusion gradient
Mass transport
The ends of the tracheoles are filled with water
How to insects move respiratory gasses in and out of the tracheal system using diffusion?
Cells respire and use up oxygen so it’s concentration at the ends of tracheoles is low
Diffusion gradient is created so oxygen diffuses from the atmosphere along the tracheae and tracheoles to the cell
Removal of the carbon dioxide removed occurs the same way
Why is diffusion the best method of gaseous exchange for insects?
Diffusion is air is much more rapid than in water
How to insects move respiratory gasses in and out of the tracheal system using mass transport?
Contraction of muscles in the insect squeezes the trachea
Enables mass movements of air in and out
Speeds up exchange of respiratory gasses
How to insects move respiratory gasses in and out of the tracheal system by having water in the ends of tracheoles?
During major activity, muscle cells around the tracheoles respire anaerobically
Lactate is produced which is soluble and lowers water potential of the muscle cell
Water moves into the muscles cells from the tracheoles by osmosis
The water in the tracheoles reduces in volume and so draws air in
What is the result of anaerobic respiration in insects which involved the water filled tracheoles?
Fast rate as the final diffusion is in gas not liquid
Increased rate that air is moved in
But this leads to more water evaporation
What are spiracles?
Tiny pores through which gasses enter and leave trachaea
Can be opened or closed by a valve
Why are the valves to the spiracles of tracheae not constantly open?
Gasses exchange when they are open but water also evaporated
Closing then prevents water loss
Why have fish evolved to have gills?
They are relatively large so have small SA:V ratio
So their body surface is not adequately to supply and remove their respiratory gasses
What makes fish gas-tight?
They have a waterproof outer covering
Describe the structure of the gills.
Located in the fishes body
Stacked full filaments
Gill lamellae are at right angles to the filaments
What is the purpose of gill lamellae?
Increase surface area
How does water enter and leave a fish?
Taken in through mouth
Forced over gills
Out through openings on each side of the body
What is concurrent flow?
The flow of the water over the gill lamellae is opposite to the flow of the blood within them
What is the purpose of concurrent flow?
Ensures maximum possible gas exchange
Maintain a diffusion gradient all the way across the gill lamellae
How does concurrent flow increase gas exchange?
Blood well loaded with oxygen meets water with maximum oxygen concentration so diffusion from water to blood occurs
Blood with little oxygen meets water with most of its oxygen removes and diffusion from water to blood still takes place
