[A] : In lower invertebrates the digestion is intracellular while in higher forms it is extracellular .
[R] : Extracellular digestion is highly evolved process , it takes place in gut .

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the assertion-reason question, we will analyze both the assertion and the reason step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "In lower invertebrates, digestion is intracellular while in higher forms it is extracellular."
- Intracellular digestion occurs within the cells, which is typical for simpler organisms like bacteria and sponges (lower invertebrates).
- Extracellular digestion happens outside the cells, in a digestive system or gut, which is characteristic of more complex organisms (higher forms) such as mammals, reptiles, and amphibians.

2. **Understanding the Reason**:
- The reason states that "Extracellular digestion is a highly evolved process; it takes place in the gut."
- This is true because higher organisms have developed specialized organs (like the alimentary canal) for digestion, allowing for more efficient breakdown and absorption of nutrients.

3. **Evaluating the Truth of Both Statements**:
- Both the assertion and the reason are true statements.
- The assertion correctly describes the difference in digestion between lower invertebrates and higher forms.
- The reason correctly explains that extracellular digestion is more evolved and occurs in specialized structures (the gut).

4. **Determining the Relationship**:
- The reason provides a correct explanation for the assertion. The evolution of digestive processes from intracellular to extracellular is indeed a reflection of the complexity of the organisms.

5. **Conclusion**:
- Since both the assertion and the reason are true, and the reason correctly explains the assertion, the correct answer is:
- **Both assertion and reason are true, and the reason is a correct explanation of the assertion.**

### Final Answer:
**Option A: Both assertion and reason are true; reason is a correct explanation.**

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