gas exchange in plants and insects Flashcards
what is the gas exchange surface in a leaf?
spongy mesophyll
how does a leaf provide a short diffusion pathway and large SA?
the leaf is only a few cells thick and is very long
how does carbon dioxide enter the leaf?
carbon dioxide diffuses into the intercellular spaces of the leaf via stomata, through the cell wall and cell membrane to enter the
spongy mesophyll cells
how does the spongy mesophyll give a large surface area?
air spaces give a large SA over which the CO2 can diffuse into the cells
if cells were tightly packed together little or their surface would be in contact with air
how is a concentration gradient maintained in a spongy mesophyll cell?
within the cells, carbon dioxide is used for photosynthesis so concentration of CO2 is maintained at a lower conc in the cell than within the intercellular spaces.
why do plants not need complex features for gas exchange?
large surface area from many leaves and lower metabolic requirements than animals
how is water loss from exchange surfaces reduced in a leaf?
waterproofing from the waxy cuticle and guard cells that can close the stomata
how does air enter and leave insects?
via spiracles that open in high concentrations of carbon dioxide and close to reduce water loss
how does air travel after entering through spiracles?
via diffusion down trachea and then along smaller branches called tracheoles
what is the actual gas exchange surface in insects?
tracheal wall
how is a large surface area provided for efficient gas exchange in insects?
tracheoles branch from larger tracheae (many branches= large SA)
how is a short diffusion pathway provided in insects?
one cell thick tracheole walls
every cell in close contact with tracheoles
how is a steep concentration gradient maintained in insects for a fast rate of diffusion?
oxygen in cells is used in resp, so lower conc of oxygen in the cell (lower than conc in tracheoles), so oxygen diffuses from tracheoles to cells
what system do larger insects and flying insects have and what does this mean?
abdominal pumping system- when muscles in the abdomen wall contract, it raises the pressure so air can flow down pressure gradients in the tracheoles- bulk movement
pushing CO2 out and O2 in
what does flying require?
rapid muscle contraction and therefore high levels of energy
so higher rates of anaerobic respiration
what is the bad thing about higher rates of anaerobic respiration in insects?
produces lactic acid which is soluble
The ends of the tracheoles are fluid filled. What happens to this fluid during exercise and why?
during exercise muscle cells undergo anaerobic respiration which produces lactic acid
lactic acid is soluble and lowers the water potential of cells, so that it is lower than in the tracheoles
therefore, water moves into the cells from the tracheoles via osmosis
what is the benefit of water moving out of the tracheoles via osmosis?
water in the ends of tracheoles decreases in volume, so more air can be drawn in
this means the final diffusion pathway is through gas not liquid, so diffusion of oxygen is faster.
why is diffusion faster in a gas phase than liquid?
particles are more spread out so oxygen can diffuse through quicker
what things reduce water loss in an insect?
-small SA:V ratio to minimise area water is lost over
-waterproof coverings
-spiracles close to reduce water loss
how do plants reduce water loss?
-waxy cuticle
-close stomata when necessary
how do plants with limited supply of water control water loss?
evolved a range of other adaptations to limit water loss through transpiration,
such as; thick waxy cuticle, rolling up of leaves, hairy leaves, stomata in pits, reduced SA:V ratio of leaves
what are xerophytes?
plants that are adapted to living in areas where water is in short supply
