Digestive systems mechanically and chemically
degrade food into small molecules that can be absorbed, along with water, into
the internal environment. These systems also expel the undigested residues from
the body. Incomplete digestive systems are a saclike cavity with one opening.
Complete digestive systems are a tube with two openings and regional
specializations in between. Structural variations in bills, teeth, and regions
of the gut are adaptations that allow an animal to exploit a particular type or
types of foods.
Digestive system (Tract)
The digestive tract is the area where digestion
takes place.
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The digestive tract varies widely in
complexity from species to species.
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The most primitive form found in
nematodes is simply a tubular gut with no specialized features.
•
The slightly more advanced digestive
tract found in earthworms includes specialized areas for ingestion, storage,
fragmentation, digestion, and absorption.
•
The most advanced digestive tracts,
found among the vertebrates, exhibit specialization on a much greater scale.
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