Gas Exchange in Earthworms (annotated snippets of E exemplar)
Earthworms are soft bodied cylindrically shaped animals with
segments of the Megadrilacea order which is made up of a large
number of different species. They are usually found living within soil.
Their digestive system is of a one way gut type. It carries out gas
exchange through its skin surface and has a simple closed blood
circulatory system. Earthworms are hermaphroditic; this means that
each individual has the gonads of both male and female. Like all
invertebrates it doesn’t have an internal skeleton, instead it maintains
its structure with chambers that are filled with fluid. Collectively these
function like a hydro skeleton……………………..
Excerpt showing named
description of one of
the animal groups
studied.
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The earthworm has its moist cuticle (skin surface) as its gas exchange
structure. The moisture on this surface allows gaseous oxygen from
the atmosphere to dissolve. This is necessary for the diffusion of
oxygen into the body to occur. The cuticle is thin allowing for rapid
diffusion of dissolved oxygen into the body. The long tube-like body of
the earthworm allows for a large gas exchange surface compared to
the volume of the body of the earthworm – this maximises the area
over which gas exchange can occur. Together these three adaptations
allow the earthworm to maximise its rate of gas exchange. This allows
for maximal oxygen uptake thus allowing for a high enough rate of
respiration in order for the earthworm to produce enough energy
(ATP) in order to run its life processes (such as moving around to find
food / a mate) and support its metabolic demands…….
Earthworms would not survive well out of their habitat. If removed
from their burrows their skin would dry up in the elevated above
ground temperatures. This would prevent the dissolving of oxygen and
thus oxygen uptake and then respiration would halt. The earthworm
would not receive sufficient ATP to run its body processes and it would
die. In order to prevent this an earthworm stays underground and in
times of extreme dryness it may burrow further into the ground to find
a source of moisture in order to avoid desiccation……
Excerpt showing several
explanations of the
adaptations of the
respiratory surface, and
moisture.
Excerpt showing linked
statements of
adaptations (moisture,
underground behaviour)
linked to way of life