A student observed a water drop under microscope. He found a photosynthetic organism. Its cell wall forms two overlapping shells which fit together as in soap box. Which of the following organisms is is

Options

A. Euglenoids
B. Dinoflagellate
C. Sporozoans
D. Diatoms.

Answer

To solve the question, we need to identify the photosynthetic organism observed by the student under the microscope based on the description provided. Here’s a step-by-step breakdown of the solution:

### Step 1: Analyze the Description
The organism observed has a cell wall that forms two overlapping shells fitting together like a soap box. This is a key characteristic that will help us narrow down the options.

### Step 2: Review the Options
The options given are:
1. Euglenoids
2. Dinoflagellates
3. Sporozoa
4. Diatoms

### Step 3: Evaluate Each Option
- **Euglenoids**: These organisms do not have a cell wall; instead, they have a flexible pellicle. Therefore, they do not fit the description.

- **Sporozoa**: This group of protozoans also lacks a cell wall. Thus, they are not the correct answer.

- **Dinoflagellates**: They possess a cell wall known as theca, which is made of cellulose and consists of plates. However, the structure does not match the description of two overlapping shells like a soap box.

- **Diatoms**: Diatoms are known for their unique cell wall structure, which consists of two thin overlapping shells made of silica. This structure indeed fits together like a soap box, and they are also photosynthetic.

### Step 4: Conclusion
Based on the analysis, the organism that fits the description of having a cell wall that forms two overlapping shells and is photosynthetic is **diatoms**. Therefore, the correct answer is option number four: **Diatoms**.

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