Gas exchange and SA:V Flashcards
What are examples of things that need to be exchanged?
- respiratory gases eg. oxygen and carbon dioxide
- nutrients eg. glucose, amino acids, fatty acids and glycerol
- excretory products eg. urea, salt
- heat
What are the 2 types of exchange?
active eg. active transport and co-transport
passive eg. diffusion and osmosis
What is fick’s law?
surface area x difference in concentration divided by length of diffusion path
Describe the relationship between size and surface area to volume ratio of organisms
the larger the size of an organism, the smaller the SA:V ratio
How is gas exchange achieved in single-celled organisms eg. amoeba?
- 1 cell therefore very large SA:V ratio
- folds in surface called pseudopods - increase surface area
- thin cell membrane - short diffusion distance
- partially permeable which allows movement of O2 and CO2 by simple diffusion
- engulfs food using pseudopods for nutrients
What are xerophytic plants?
Plants adapted to dry conditions with little water
What are the adaptations of xerophytic plants?
Thick - larger diffusion distance so little water loss
Rolled up leaves - traps air within the roll which becomes saturated with water vapour, so has a very high water potential - no water potential gradient therefore no water loss
Hairy leaves - traps still, moist air on the leaf surface which reduces water potential gradient so less water loss through evaporation
Stomata in grooves - trap still moist air which reduces water potential gradient
Small SA:V ratio - reduced water loss
Root system - deep to penetrate water table and shallow to absorb rainfall
How have insects evolved for gas exchange?
- insects have evolved an internal network of tubes called trachae, which are supported by strengthened rings to prevent them from collapsing
- trachae divide into smaller tubes called tracheoles which extend throughout the body tissues
- oxygen is brought directly into respiring tissues as there is a short diffusion distance from tracheoles to body cells
How do gases move into an insect along a diffusion gradient?
- when cells respire, oxygen is used up so concentration of oxygen at the ends of tracheoles falls
- this creates a diffusion gradient that causes oxygen to diffuse from the atmosphere along the trachae and tracheoles to the cells
- CO2 is produced by cells during respiration
- this creates a diffusion gradient in the opposite direction which causes CO2 to move along tracheoles and trachae from cells to the atmosphere
How do gases move into an insect through mass transport?
rhythmic contraction of abdominal muscles can squeeze the trachea, ‘pumping’ air in and out
How do gases move into an insect due to the ends of tracheoles being filled with water?
- during periods of major activity, muscle cells around the tracheoles respire and carry out anaerobic respiration
- this produces lactate which is soluble and lowers water potential of muscle cells, therefore water moves into the cells from tracheoles by osmosis
- water in the ends of tracheoles decreases which draws air further into them
- this means the final diffusion pathway is in a gas rather than liquid phase, so diffusion is more rapid
How do gases enter and leave the trachae?
Through tiny spores called spiracles on the body surface which are opened and closed by valves. Insects close spiracles to prevent water loss.
Spiracles open to air filled pipes called trachae which branch into trachaeoles and capillaries
How do insects maintain a steep concentration gradient?
Muscle cells rapidly use up oxygen during respiration leading to a low oxygen concentration in muscles. There is always a high concentration of oxygen in the air
How do insects have a large surface area?
- small - large SA:V ratio
- large SA through legs/wings
- lots of trachae and trachaeoles
How do insects have a short diffusion pathway?
There is a direct link between tracheoles and muscle cells
What is the structure of fish gills?
- made up of gill filaments
- gill lamallae which increases the surface area of the gills