A : Holophytic protistans are important phytoplanktons and they contibute 80% of the total photosynthesis.
R : They lack chemosynthetic nutrition and utilize non sulphur organic compound as the source of electron and proton in carbon assimilation.

Options

A. If both assertion & reason are true and the reason is the correct explanation of the assertion
B. If both assertion & reason are true but the reason is not the correct explanation of the assertion
C. If assertion is true statement but reason is false
D. If both assertion and reason are false statements

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Holophytic protistans are important phytoplanktons and they contribute 80% of the total photosynthesis."
- Holophytic protists are indeed a type of autotroph that perform photosynthesis, primarily using sunlight as their energy source.

2. **Evaluating the Assertion**:
- It is known that phytoplankton, including holophytic protists, play a crucial role in the aquatic ecosystem and contribute significantly to global photosynthesis.
- The claim that they contribute 80% of the total photosynthesis is accurate, as phytoplankton are responsible for a large portion of the Earth's oxygen production.

3. **Understanding the Reason (R)**:
- The reason states that "They lack chemosynthetic nutrition and utilize non-sulfur organic compounds as the source of electron and proton in carbon assimilation."
- Holophytic nutrition is characterized by the use of light energy and inorganic carbon (like CO2) for photosynthesis, rather than relying on chemosynthesis.

4. **Evaluating the Reason**:
- The statement about lacking chemosynthetic nutrition is correct; holophytic protists do not utilize chemosynthesis.
- However, the part about using "non-sulfur organic compounds" as a source of electrons and protons is misleading. Holophytic organisms typically use water (H2O) as the electron donor in photosynthesis, not organic compounds.

5. **Conclusion**:
- The assertion is true, while the reason is false due to the incorrect explanation of the source of electrons and protons in carbon assimilation.
- Therefore, the final answer is: Assertion (A) is true, and Reason (R) is false.

### Final Answer:
Assertion is true, and Reason is false.

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