Gas Exchange Flashcards
describe gas exchange in single-celled organisms (amoeba)
exchange all their gases by simple diffusion across their cell surface membrane (since they have a large enough surface area: volume and their concentration gradient is maintained by respiration.
what are the features of a specialised exchange surface
- large surface area (:volume ratio)
- very thin (short diffusion distance)
- maintains diffusion gradient (movement of environmental medium eg air and movement of internal medium eg blood)
- selectively permeable
describe gas exchange in insects
- insects have a network of tubes (tracheae) connecting their outside surface to the internal cells
- the tracheae divide into smaller tracheoles which extend through the body tissues
- the tracheae openings are called spiracles
model answer for ‘describe how gas exchange occurs through the tracheal system in insects’
Air diffuses down through the spiracle into the trachea, then down the concentration gradient through the tracheoles. when at the muscle cells the O2 diffuses into the cells whilst CO2 diffuses out due to the concentration gradient. these concentration gradients are maintained by the respiration of the muscle cells. in larger and more active insects they do abdominal pumping, this is where abdominal muscles contract to push out air low in O2 and high in CO2, then relax to draw in air high in O2 and low in CO2 (steep conc. grad.)
how do tracheoles provide a good exchange surface?
- many highly branched tracheoles means no cell is too far from a tracheole, which provides a short diffusion distance for oxygen and carbon dioxide
- many, small, branched tracheoles provides a large surface area for diffusion of oxygen and carbon dioxide
- respiration of muscle cells maintains concentration gradient for oxygen and carbon dioxide
- abdominal muscles draw air high in oxygen and low in carbon dioxide in to replace air low in oxygen and high in carbon dioxide maintains concentration gradients for carbon dioxide and oxygen
why do fish not exchange gases over their surface?
low surface area to volume ratio
what are gills in fish made from?
gills are made up of gill filaments, along the upper and lower surface of each gill filament and standing up at right angles to it are gill lamellae
describe what countercurrent flow is
as water passes through the gills, it flows between gill lamellae. the blood in the gill lamellae flows in the opposite direction. this is called countercurrent flow.
describe and explain the advantage of a countercurrent flow
Blood and water flow in opposite directions so blood always flows past water that has a higher O2 concentration. so the diffusion gradient is maintained across the whole length of the gill lamellae for O2 to diffuse from the water into the blood.
how do gills provide a good exchange surface?
- lots of gills filaments, each with lots of lamellae provides a large surface area for gas exchange
- thin lamellae and well supplied with lots of blood capillaries provides a short diffusion distance
- countercurrent flow maintains diffusion gradients for O2 and CO2 all the wall along the gill
describe how gas exchange occurs in leaves in both the dark and light
- gas exchange is for photosynthesis and respiration
- dark only respiration occurs, O2 diffuses in, CO2 diffuses out (down conc. grad.)
- light photosynthesis + respiration occur simultaneously, gas enters and leaves through stomata on the lower epidermis of the leaf
how does the leaf structure provide a good exchange surface for gases?
- leaf is thin, has many airspaces so many cells in contact with air, lots of stomata short diffusion distance
- leaf itself is flat, has large SA, air spaces large SA to volume ratio
- rate of respiration and photosynthesis of cells maintains concentration gradients for oxygen and carbon dioxide
describe the states of stoma in light and dark?
light = open
dark = closed
