Choose the correct sequence

Options

A. (a) phytoplankton`rarr`zooplanktons`rarr`crustacean`rarr`fish
B. (b) crustaccans`rarr`fish`rarr`zooplankton`rarr`phytoplankton
C. (c) zooplanktons`rarr`phytoplanktons`rarr`crustaceans`rarr`fish
D. (d) fish`rarr`crustacean`rarr`zooplankton`rarr`phytoplankton

Answer

### Step-by-Step Solution:

1. **Identify the Producers**: In an aquatic ecosystem, the primary producers are phytoplankton. They are capable of photosynthesis due to the presence of chlorophyll.

2. **Understand the First Trophic Level**: Phytoplankton form the base of the food chain in aquatic ecosystems. They convert sunlight into energy and serve as the primary source of food for the next level.

3. **Identify the Primary Consumers**: The next level in the food chain consists of zooplankton. These organisms feed on phytoplankton and are considered primary consumers.

4. **Identify Secondary Consumers**: Following zooplankton, small fishes and crustaceans (like crabs and prawns) occupy the next trophic level. They feed on zooplankton.

5. **Identify Tertiary Consumers**: Larger fishes, including species like sharks and whales, are at the top of the food chain. They consume smaller fishes and crustaceans.

6. **Determine the Correct Sequence**: Based on the trophic levels outlined, the correct sequence is:
- Phytoplankton (Producers)
- Zooplankton (Primary Consumers)
- Crustaceans and small fishes (Secondary Consumers)
- Larger fishes (Tertiary Consumers)

7. **Select the Correct Option**: The correct answer is option A, which lists the sequence as phytoplankton, zooplankton, crustaceans, and then fish.