Zusammenfassung der Ressource
Gas exchange Systems
- Animals
- Fishes have gills
through which they
exchange gasses.
- Counter-current occurs
where water and blood flow
in the opposite directions,
via the lamellae and Gill
filaments. Oxygen diffuses into the blood
- Both these features have a large surface area
making the gas exchange more efficient and
faster.
- This happens continuously so that a
concentration gradient is maintained. This
means diffusion can occur continuously.
- Humans have lungs where gas
exchange occurs, between the
alveoli and the capillaries.
- When we inhale, our diaphragm and
external intercostal muscles
contracts, increasing the volume of
the thorax, so Oxygen diffuses in.
- When we exhale, our internal
intercostal muscles contracts,
and the others relax, decreasing
the volume but increases
pressure, forcing Carbon Dioxide
out.
- The Oxygen travels
down our trachea,
through the bronchi,
through little
bronchioles, into the alveoli.
Anmerkungen:
- Alveoli have a one cell thick, and permeable membrane, allowing efficient gas exchange and fast. There are many of them which increases their surface area.
- Due to a continuous blood circulation, a concentration gradient is maintained so that Oxygen can always diffuse into the blood.
- The Oxygen travels from the
alveoli, through the alveolar
epithelium, and through the
capillary endothelium into the
blood.
- Insects
- They have spiracles
through which their
gasses exchange,
and there are many
of them, which
increases their
surface area.
Anmerkungen:
- The spiracles open when gas exchange is requires and close when too much water is being lost, so that the insect does not get dehydrated.
- The Oxygen diffuses through into the
tracheoles where it diffuses into the cells,
ready for respiration
- Plants
- Gas exchange occurs at the stomata
(bottom of a leaf), which opens and
closes, and is controlled by the guard
cells. Stomata are gaps between
mesophyll cells, at the lower epidermis.
- Usually, the stomata closes when too much water
is being lost, and the guard cells become flaccid,
however, if water enters the plant, it becomes
turgid opening the stomata.
- Xerophytes (plants in heat)
- These have specific features that
allow them to adapt to warm
conditions, by reducing water.
- A waxy cuticle on surface to reduce evaporation.
- Sunken stomata
which traps water
vapour.
- A layer of hair on the epidermis to
reduce water vapor around the
stomata.
- Leaves reduced to spines to
reduce the amount of water
lost by evaporation via leaves.
- Single-celled organisms
- Oxygen diffuses directly into these cells, as
they are so tiny and have such a large
surface area, the diffusion pathway is very
small, and this makes the process faster.