Question

Which of the following zones of a lake is not habitat for snails, slugs and micro-organisms?
A. Littoral
B. Limnetic
C. Benthic
D. Profundal

Answer 1

Every lake has different zones where biological communities live. The zones are associated with the physical structure of that lake and divide the water body either from top to bottom or from one side to another.

Complete Answer:
Let us analyse the options to find the correct answer.
Option A: Littoral zone is the shoreline area which lies between land and open sea. It's also called the intertidal zone. This zone receives a lot of sunlight and nutrients thus supporting growth of rooted aquatic plants. The rate of photosynthesis is high here. Hence, this is the correct option.

Option B: Limnetic zone is an open water area. It extends from the portion near the surface of the lake receiving a good amount of sunlight to the portion where sunlight is not able to reach. Commonly found organisms near the surface are aquatic plants, big fishes and algae because of contact with air and high oxygen levels. Hence, this is the correct option.

Option C: Benthic zone is the bottom most zone of a lake. This zone is rich in sediments and decomposition of dead and organic matter by bacteria takes place here. The upper surface of this zone is usually a habitat of invertebrates like snails and slugs. Also found here are microorganisms like bacteria. Hence, this is an incorrect option.

Option D: The upper part of the limnetic zone is called the euphotic zone while the lower one is called profundal zone. Profundal zone receives less sunlight than the euphotic zone and rate of respiration is higher than the rate of photosynthesis here. Very few organisms are found here due to lack of oxygen and low temperatures. Hence, this is the correct option.

Thus, the correct options are A) Littoral zone, B) Limnetic Zone and D) Profundal Zone.

Additional information:
- Snails and Slugs belong to the phylum Mollusca. They usually live near or in the benthic zone.
- Micro-organisms are found in the benthic zone due to abundance of dead and decaying matter.

Note:
- The study of inland water systems and their biological, physical, chemical and geological characteristics is called Limnology.
- Physical factors like light, temperature and oxygen influence the types of organisms found in different zones of a lake.