Unit 2

• Submerged Floating Hydrophytes: Plants that remain entirely submerged beneath the water surface without root attachment to the bottom sediments, drifting freely with water currents.
• Representative Taxa: Ceratophyllum (Ceratophyllum demersum, coontail) and Utricularia (bladderwort) are classic submerged suspended/floating hydrophytes.
• Other Ecological Classes: Trapa and Wolffia are surface-floating hydrophytes; Hydrilla is typically submerged and rooted.

Correct option: (1) Ceratophyllum

• Statement (C) is Correct: Nektons are free-swimming aquatic organisms (such as fishes, amphibians, and larger swimming insects) capable of navigating independently of water currents.
• Statement (D) is Correct: Neustons are specialized organisms inhabiting the air-water interface / surface film tension (e.g., Gerris water striders).
• Why (A) and (B) are Incorrect: The profundal zone (A) is deep, aphotic, and devoid of photosynthetic autotrophs. In littoral and limnetic zones (B), gross primary production exceeds community respiration ($P/R \gt 1$), whereas in the profundal zone respiration exceeds production ($P/R \lt 1$).