SA:V & Exchange in insects Flashcards
Essential features of an exchange surface for rapid exchange?
- Large surface area compared to the volume of the organism (SA:V ratio)
- Thin - short diffusion pathways so diffusion is rapid
- Selectively permeable - to allow select materials to cross
- Maintenance of steep concentration gradients (ie. for diffusion) - may require a transport system to move the internal and external environments
Single celled organisms?
- hv very large SA in comparison to vol so - big SA for exchange
- smaller distance from the cell-surface membrane to the centre of the cell
- short diffusion distances inside cell
- so simple diffusion is rapid enough for the cell’s needs - across organism’s surface
Larger organisms?
- smaller SA:V so
- larger dis from middle of body to outside - longer diffusion pathways so
- slower rates of diffusion
- also hv higher metabolic rate so - demand efficient transport of waste out of cells & reactants into cells (as have more cells)
- instead of of cells growing in size for organism to grow - ten to divide & remain small in order to remain higher SA:V
Adaptations to increase SA:V (increase SA w/o reducing vol tm)?
- villi & microvilli - absorption of digested food
- alveoli & bronchioles - gas exchange
- spiracles & tracheoles - gas exchange
- gill filaments & lamellae - gas exchange in fish
- flat/thin/wide leaves/flatworm/elephant ears - gas exchange (short diffusion pathways)
- many capillaries - capillary network - large no. of capillaries so - large SA - gas exchange
- root hairs on roots - absorption of molecules
Metabolism definition?
all the chemical processes that occur within a living organism in order to maintain life
- includes anabolism (building-up) & catabolism (breaking-down) - needs energy
Relationship between SA & metabolic rate?
metabolic rate: amount of energy expended (used) in a given time period (usually 24 hrs)
- as ts energy provided by respiration - can be measured by:
- O2 consumption
- CO2 production
- heat production
Why is the metabolic rate of organisms with a lower mass higher than larger animals?
- lower mass organisms hv higher SA:V so - lose more heat (as more SA to lose heat from)
- so - to maintain body temp - must respire more
- so - metabolic rate per unit of body mass higher (than larger animals)
Terrestrial insects?
- hv an exoskeleton made of: hard fibrous material - for protection & lipid layer - to prevent water loss
- exoskeleton: made of chitin (minimises water loss but - impermeable to gases) so…
- hv internal network of tubes aka tracheal system - which respiratory gases move in & out of
Limiting water loss in insects?
- small SA:V where water evaporates from
- waterproof exoskeleton
- spiracles can open & close to reduce water loss (where gases enter & water evaporates from)
Tracheal system - Spiracles?
- round openings/pores on body surface
- open & closed by valve
- run along length of abdomen
- O2 in, CO2 out
- trachea attached to these
Tracheal system - Trachea?
- network of internal tubes
- trachea tubes hv rings of chitin within them to strengthen them & keep open aka prevent trachea collapsing
Tracheal system - Tracheoles?
- aka trachea branched into smaller tubules
- extend thru all body tissues - carrying O2 directly to respiring cells & removing CO2
- short diffusion pathway between tracheoles & body cells
1st method of moving gases in tracheal system?
- Simple diffusion as - when cells respire - use up O2 & produce CO2 - create conc. gradient of gases inside insect (tracheoles) compared to outside (atm)
- due to conc. gradient, small size so - dis between tracheoles & outside is small - diffusion occurs
2nd method of moving gases in tracheal system?
- Mass transport:
- abdominal muscles (muscles within abdomen) contract and relax - pump to move gases on mass in & out of tracheal system (to atm) aka ‘abdominal pumping’
- increases exchange efficiency as: more air/O2 enters quicker so - maintains conc. gradient
Abdominal pumping & pressure?
- abdominal pumping in tubes is linked to CO2 release
- pumping raises pressure in body
- air/CO2 pushed out of body OR CO2 moves down pressure gradient
3rd method of moving gases in tracheal system?
- when flying - muscle cells start respiring anaerobically - producing lactate (aka lactic acid)
- this lowers water potential of cells so - water moves from tracheoles into cells by osmosis
- this decreases vol of water in tracheoles so - more air from atm drawn in (lower vol of water so -> lower pressure in tracheoles compared to atm -> forces in/faster diffusion of more air from atm)
Movement of gases through the tracheal system is caused by?
- Concentration/diffusion gradients
- Contraction of muscles around the tracheal system
- Ends of tracheoles are filled with water
Adaptations in insects for efficient diffusion?
- highly branched/large no. fine tracheoles (and spiracles) - large SA
- walls of tracheoles r thin & short distance between spiracles & tracheoles - short diffusion pathway to cells
- body can be moved (by muscles) to move air so -maintains diffusion/use of O2 & production of CO2 sets up steep diffusion gradients
