Page 28 - 11-Bio-14 Transport

14. Transport eLearn.Punjab

TRANSPORT IN ANIMALS

Unicellular animals have maximum surface area to volume ratio; and most of the substances move
into or out of their bodies by simple diffusion, osmosis, active transport, and facilitated diffusion.
So there are no special transport systems involved. Same is true of simple multicellular animals
which are aquatic. But complex multicellular animals possess highly organized, and well developed
transport system, in the form of blood vascular system.

Transportation in Hydra

It is fresh water in habitat. The body is two layered;
the outer ectoderm and inner endoderm; in between
them is mesogloea which is non-cellular. The outer
surfaces of the ectoderm cells are exposed to the
water in which the animal lives. Water, dissolved 02,
and food is taken into the coelenteron(enteron) of
Hydra by the movement of tentacles, and flagella
which are present in most cells of endoderm.

The materials and food may be absorbed or taken
up by endocytosis into endodermal cells. The
indigestible and partly digested food is removed
by exocytosis from these cells, into digestive cavity
(coelenteron). Ectodermal cells get food from
endodermal cells by diffusion.

The ectodermal cells directly exchange materials
with the surrounding water (Fig 14.14). They also
get nutrients from endodermal cells.

Fig.14.14 Hydra

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