Which among the following is the second trophic level in a lake?

The correct answer is Option (1) → Zooplankton

In a lake the producers are the phytoplankton, which form the first trophic level. The animals that feed on them, the zooplankton, are herbivores (primary consumers) at the second trophic level.

Option (1) Zooplankton — Correct. Zooplankton feed on phytoplankton, so they are primary consumers at the second trophic level.

Option (2) Shark — Incorrect. The shark is a large carnivore that eats other fishes, so it sits at a high trophic level. Sharks also live in the sea, not in a lake.

Option (3) Phytoplankton — Incorrect. Phytoplankton make their own food by photosynthesis. They are producers at the first trophic level.

Option (4) Fishes — Incorrect. Fishes are shown as secondary consumers at the third trophic level, since they feed on the zooplankton.

Note: Zooplankton, grasshopper and cow sit together in one small box of Figure 12.2. A figure like this can supply a whole question, so look at its examples as carefully as at the text.

NCERT Extract:
Energy Flow – “Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms. Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third (Figure 12.2).”

Figure 12.2 Diagrammatic representation of trophic levels in an ecosystem