Upper part of sea/aquatic ecosystem contains

Options

A. Plankton
B. Nekton
C. Both(a) and(b)
D. Benthos

Explanation

**Step-by-Step Solution:**

1. **Understanding the Aquatic Ecosystem**: The aquatic ecosystem is divided into different layers, with the upper part being crucial for various forms of life. This layer is primarily where sunlight penetrates, making it suitable for photosynthesis.

2. **Identifying Key Terms**: In the upper part of the aquatic ecosystem, we encounter two main categories of organisms:
- **Plankton**: These are small organisms that drift with water currents. They can be further classified into:
- **Zooplankton**: These are animal plankton that float in the water. Examples include small crustaceans and larval fish.
- **Phytoplankton**: These are plant-like organisms that perform photosynthesis, such as diatoms and dinoflagellates.
- **Nekton**: These are larger, actively swimming organisms that can move independently of water currents. Examples include fish (like bony fishes and sharks) and marine mammals.

3. **Distinguishing Between Organisms**: It’s important to note that:
- **Plankton** are primarily found in the upper layers and are either zooplankton or phytoplankton.
- **Nekton** are also found in the upper layers but are capable of swimming against currents.
- **Benthos** refers to organisms that live at the bottom of the aquatic ecosystem and are not part of the upper layer.

4. **Conclusion**: Therefore, the upper part of the sea or aquatic ecosystem contains both plankton (zooplankton and phytoplankton) and nekton. The correct answer to the question is that the upper part contains both A (plankton) and B (nekton).

**Final Answer**: The upper part of the sea/aquatic ecosystem contains both plankton (zooplankton and phytoplankton) and nekton.

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