Question

Flame cells are the excretory organs of
A. Prawn
B. Planaria
C. Silverfish
D. Hydra

Answer 1

Hint: Flame cells are the specialised secretory cells found in the simplest organisms. They function like kidney, removing waste material. Bundles of flame cells are called protonephridia. The organisms in which the flame cells are found are very small and basic to have a dedicated excretory system.

Complete answer:
The flame cells have a nucleated cell body with a "cup-shaped" projection. They are flagellated. The beating of flagella resembles a flame that gives the cell its name. The cup is attached to a tube cell, whose inner surface is coated in cilia. The cilia help to move liquid through the tube cell. The tube opens externally through a nephroscope into an excretory bladder.

The function of flame cells is to regulate osmotic pressure and maintain its ionic balance. These cells are the excretory cells of the simplest freshwater invertebrates including flatworms, rotifers, and nemerteans. Planaria is a flatworm of the traditional class turbellaria.

Prawn- In the case of prawn, the excretory organ is called the green glands. They excrete ammonia. Thus this answer is incorrect.
Silverfish belongs to the phylum Arthropoda. The excretory organ is a malpighian tubule. Thus the answer is incorrect.
Hydra does not have any excretory organs. The waste products like ammonia are removed through the body surface with the help of diffusion. Thus this answer is incorrect.

Therefore the answer to this question is option D- Planaria.

Note: The excretory system of planaria consists of two tubules connected to a highly branched duct system that leads to pores located all along the sides of the body. The filtrate is excreted through these pores. The cells in these tubules are called flame cells or protonephridia.