Question

In Hydra, egestion of undigested food and excretion of nitrogenous wastes occur through
A. Mouth and Tentacles
B. Mouth and Body Wall
C. Mouth and Mouth
D. Body Wall and Body Wall

Answer 1

Hint: Hydra has the Blind Sac organization, so it does not have any specialized organs for digestion or excretion.

Step by step answer:Hydra belongs to the class of Cnidaria. These animals have a Radial symmetry and Blind Sac Organization. Radial symmetry indicates that their mouth is at the top of their body. The Blind Sac organization says that they have a single opening only that acts as both Mouth and Anus. The process of digestion in Hydra is both Extracellular and Intracellular. The digestion begins as an Extracellular process where the food reaches the cavity through Hypostome. Here the digestion occurs through the enzymes that are secreted by the gland cells of the Endoderm.
Now, this semi-digested food is further passed to the Nutritive cells or the Endothelial-vascular cells or the Circular cells, of the endoderm. These cells digest the food further with the help of their vacuoles.
The undigested food now is in the form of big chunks and hence it cannot be expelled out from the body wall. So, it is egested by the Mouth.
However, the metabolized food products are converted into the nitrogenous wastes which are usually in the gaseous form. As these molecules are very small, they are excreted from the body wall only.
Hence, in Hydra, the egestion of undigested food occurs through the mouth and the excretion of nitrogenous wastes occurs through the body wall.
Thus, the correct answer is option (B)

Note: Egestion is the process of expelling the undigested food out from the body. Egestion differs from the Excretion in the aspect that during excretion the metabolic wastes are excreted out whereas, in Egestion, the undigested, leftover food is expelled out.