Q.16. In term of food capture, which sponge cell is most similar to cnidocyte of a cnidarian.
Answer: Option B [choanocyte]
Choanocyte is the flagellated cell having a protoplasm collar at the base of the flagellum. These cells lined the interior of asconoid, syconoid and leuconoid type of sponges. By the cooperative movement of flagella, these cells generate the pressure due to which water flows through the sponges' pores, into the spongocoel and which out through the osculum.
Q.17. Sponges are most accurately described as
Answer: Option B [Marine filter feeders]
Most of the sponges i.e. more than 99% of the sponges found in the marine environment that’s why they are commonly known as marine filter feeders.
Q.18. How many of the following are characteristics of at least some members of phylum Cnidaria?
Answer: Option D [Four of these]
Members of phylum Cnidaria has a gastrovascular cavity, having both polyp and medusa stage of life and these members have cnidocytes.
Q.19. Which of the following is true of members of phylum Cnidaria?
Answer: Option D [They may use a gastrovascular cavity as a hydrostatic skeleton.]
The gastrovascular cavity is the primary organ of digestion and circulation in phylum Cnidaria. The fluid-filled this cavity is also used as a hydrostatic skeleton.
Q.20. The organ of respiratory gas exchange in oligochaetes is
Answer: Option C [The skin]
Oligochaetes (earthworms) exchange the respiratory gases directly through their skin. They don’t have any specific respiratory organ. The land living oligochaetes it is necessary to keep their body surface moist for gas exchange.
Q.21. Against which structure do the circular and longitudinal muscles of annelids work?
Answer: Option E [Hydrostatic skeleton]
The hydrostatic skeleton is found in the soft animals where their fluid-filled body cavity surrounded by the muscles.