All desmids are found in marine habitat but diatoms are found as phytoplankton large in deep lakes .

Answer

### Step-by-Step Solution:

1. **Understanding the Organisms**:
- Desmids are a type of green algae that are primarily found in freshwater environments such as ponds, rivers, and lakes.
- Diatoms are a group of microalgae that are found in both marine and freshwater environments but are commonly associated with phytoplankton in deep lakes and oceans.

2. **Habitat Analysis**:
- The statement claims that "all desmids are found in marine habitat." This is incorrect because desmids are predominantly found in freshwater habitats, not marine ones.
- The statement about diatoms being found as phytoplankton in large deep lakes is correct, as diatoms thrive in various aquatic environments, including deep lakes.

3. **Photosynthesis and Nutrition**:
- Both desmids and diatoms are autotrophic organisms, meaning they produce their own food through photosynthesis using chlorophyll.
- While diatoms can be found in benthic (bottom-dwelling) environments, they are also prevalent in the water column as phytoplankton, where they utilize sunlight for photosynthesis.

4. **Conclusion**:
- Since the statement incorrectly identifies the habitat of desmids, it can be concluded that the statement is false. Therefore, the correct answer is that the statement is false.

### Final Answer:
The statement "All desmids are found in marine habitat but diatoms are found as phytoplankton large in deep lakes" is **false**.

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