Adaptations for gas exchange (Human gas exchange (Alveoli (Large SA, gases…
Adaptations for gas exchange
Diffusion of gases happens on a respiratory surface, organisms must have a large SA:V
They must be permeable, thin, steep concentration gradient.
Earth worm is cylindrical so SA:V is smaller than a flat worms, secretes mucus to keep skin moist, low oxygen requirement, haemoglobin present in it's blood.
Amphibians skin is moist, capillary network just below to skin, when animal is active, lungs work.
Reptiles, lungs have more complex internal structure, increasing area for gas exchange.
Birds inhale into rear air sac, air expelled into lungs, bird inhales again, air moves through lungs into front air sac and expelled by them.
Do not have a counter current flow(parallel flow), they must keep swimming and only part of gill is used. Parallel flow means an equilibrium is met quickly.
The mouth opens, operculum closes, mouth floor is lowered to lower the pressure, water flows in, mouth closes, operculum opens, mouth floor raises, water flows over the gills into the operculum cavity.
They have four pairs of gills, each supported by a gill arch, along each arch are many gill filaments. On the gill filaments are gill plates (held apart by water flowing over them) provide a large SA.
Counter current flow is when the blood in the capillaries flow in an opposite direction to the water that flows over the gills. About 80% of the oxygen diffuses into the blood as a partial pressure is maintained.
Human gas exchange
Inhalation-external intercostal muscles contract, ribs pulled up and outwards, diaphragm muscles contract, increase thorax volume, reduces pressure, air forced into lungs.
Exhalation- external intercostal muscles relax, ribs move down and inwards, diaphragm muscles relax, domes down, decrease thorax volume, pressure increased, air forced out.
Lung tissue is elastic. pleural membranes between is a cavity containing pleural fluid to reduce friction. Alveoli coated with surfactant, keeps the alveoli moist.
Large SA, gases dissolve in the surfactant, one cell thick squamous epithelium, extensive capillary network surrounding it. capillary walls one cell thick.
Oxygen diffuses into the red blood cells and carbon dioxide diffuses out of the plasma.
Have exoskeleton which prevents them from using skin as a gas exchange surface as it is waterproof.
Holes in the sides called spiracles, lead to a system of branched chitin lined airways called tracheoles., at rest the insect relies on diffusion, There is fluid at the end of the tracheoles in which the gases dissolve.
Gas exchange in plants
during the day photosynthesis and respiration takes place but at night, only respiration takes place. Gases diffuse through the stomata.
Adaptations of the leaf - large SA, thin, palisade cells elongate, chloroplasts can move within palisade layer, spongy mesophyll has air spaces.
Stomata are mostly on the lower epidermis, surrounded by guard cells that have unevenly thick cell walls, the inner wall is thicker. If guard cells become turgid the stomatal pore opens. If guard cells become flaccid the pore closes.
Chloroplasts in guard cells produce ATP, active transport of potassium ionsinto the guard cells, stored starch converted to malate, these ions lower the water potential in the cells which cause water to move into them by osmosis. Guard cells become turgid and a pore appears.At noght this reverses and the pore closes.
Plants lose water through stomata by transpiration