3.3.2 Gas exchange Flashcards
what type of gas exchange system do terrestrial insects have?
a tracheal system
what are the three features of an insect’s tracheal system?
- spiracles
- tracheae
- tracheoles
what are spiracles?
- round, valve-like openings which run along the length of the abdomen
- oxygen and carbon dioxide enter and leave via the spiracles
- the tracheae attach to these openings
what are tracheae?
- a network of internal tubes
- tubes have rings within them to strengthen them and keep them open
tracheae branch into…
smaller tubes, deeper into the abdomen of the insect called tracheoles
what are tracheoles?
small tubes which extend throughout all the tissues in the insect to deliver oxygen to all respiring cells
what are the three methods of moving gases in the tracheal system?
- diffusion
- mass transport
- creating a pressure gradient
how do gases move in the tracheal systems by diffusion?
- when cells respire, they use up oxygen and produce carbon dioxide
- this creates a concentration gradient (of carbon dioxide) from the tracheoles to the atmosphere
how do gases move in the tracheal systems by mass transport?
insects contract and relax their abdominal muscles to move gases
do gases move in the tracheal systems by creating a pressure gradient?
- when the insect is in flight, muscle cells start to respire anaerobically to produce lactate
- this lowers the water potential of cells, so water moves from the tracheoles into the cells by osmosis
- less water increases the volume of gas in the tracheoles which decreases the pressure
- as a result, more air from the atmosphere is drawn in down a pressure gradient
what are the 3 key adaptations of the tracheal system for efficient diffusion?
- large number of fine tracheoles –> large surface area
- walls of tracheoles are thin and there is a short distance between spiracles and tracheoles –> short diffusion pathway
- use of oxygen and production of carbon dioxide –> steep diffusion gradients
what are the 2 key adaptations of insects to limit water loss?
- have a waterproof exoskeleton
- spiracles can open and close
describe the structure of the gills
- there are four layers of gills on both sides of the head, each supported by a bony arch
- the gills are made up of stacks of gill filaments
- each gill filament is covered in gill lamellae, positioned at right angles to the filament
- this creates a large surface area
what are the 3 adaptations of gills for efficient gas exchange?
- many gill filaments covered in many gill lamellae –> large surface area
- a capillary network in every lamellae and very thin gill lamellae –> short diffusion distance
- countercurrent flow mechanism –> maintains the concentration gradient
how does the countercurrent exchange principle work?
- water flows over the gills in the opposite direction to the flow of blood in the capillaries
- countercurrent flow ensures that equilibrium is not reached
- this ensures that a diffusion gradient is maintained across the entire length of the gill lamellae
describe the structures required for ventilation
- internal gills protected by an operculum
- fish takes water in through the buccal cavity
- water then flows through the pharynx and over the gill plates
- water leaves via the opercular opening on each side of the fish’s head
how does ventilation occur in a fish?
- mouth opens and operculum shuts
- water enters the buccal cavity due to decreased pressure
- mouth closes and operculum opens
- this results in increased pressure which forces water out over the gills
what is the structure of a dicotyledonous leaf from top to bottom?
- waxy cuticle
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- lower epidermis
- stomata (each one surrounded by two guard cells)
how does gas exchange occur at the stomata?
- oxygen diffuses out and carbon dioxide diffuses in
- to reduce water loss by evaporation, the stomata close at night when photosynthesis would not be occurring
what is a xerophyte?
a plant adapted to survive in environments with limited water
what are the 5 structural adaptations of xerophytes to limit water loss?
- curled leaves to trap moisture to increase local humidity
- hairs to trap moisture to increase local humidity
- sunken stomata to trap moisture to increase local humidity
- thicker cuticle to reduce evaporation
- longer root network to reach more water
what is the structure of the human gas exchange system?
trachea –> bronchi –> bronchioles in the lungs –> alveoli in the lungs
how does gas exchange take place in humans?
- oxygen diffuses out of alveoli and into blood
- carbon dioxide diffuses out of blood and into alveoli
what are the 3 key adaptations of the alveoli?
- lots of alveoli (around 300 million in each lung) so large surface area for diffusion
- alveoli epithelium are very thin so a short diffusion pathway
- each alevolus is surrounded by a network of capillaries so concentration gradient maintained
