Question

What are three functions of a Cnidarians gastrovascular cavity?

Answer 1

Hint: Organ and organ system levels began in lower animals like platyhelminthes and aschelminthes but their complexity kept on increasing from lower to higher phyla. The digestive system of animals can be of two types on the basis of complexity as an incomplete and complete digestive system.

Complete answer:
In an organism having an incomplete digestive system has only a single opening to the outside of the body serving as mouth and anus. In organisms having a complete digestive system have two openings; mouth and anus. Hence, the entry of food and exit of waste takes from two different openings.
Phylum cnidaria includes around 9,000 species. The animals of this phylum are called Cnidarians. They possess aquatic habitat as they inhabit the water bodies. They are mostly marine but few are fresh water also.
On the basis whether the animal lives singly or in association with others, the cnidarians can be either solitary or colonial. Example of a solitary cnidarian is Hydra. Examples of colonial cnidarians are Physalia, Gorgonia, Obelia,etc.
They might even be categorized as sessile or free-swimming.
The cnidarians are the radially symmetrical animals as any plane passing through the central body axis divides these animals into two identical halves.
Cnidarians have a tissue level of body organization. The tissues are arranged such that they perform the basic functions in their body. They are diploblastic animals.
The body of cnidarians bears a central gastro-vascular cavity which opens to the outside through a single opening called mouth. Mouth is an aperture present on the hypostome. Hypostome is a conical elevation present on the free end of the body.
Entry of food and exit of waste materials takes place through this single opening mouth. The gastro-vascular cavity is called so because it helps in the digestion of food as well as in the circulation of materials.
Externally the body bears elongated flexible structures called tentacles which are able to contract as well as elongate. The tentacle helps in feeding, feeling and grasping prey.

Note:
A piece of Hydra will regenerate into full Hydra if it contains a part of epidermis, gastrodermis and interstitial cells. If the body stalk of Hydra is cut transversely into several segments, then in these segments, tentacles would regenerate at the end that was close to the hypostome.