Assertion: Thorns and tendrils of Bougainvillea and Cucurbita represent homology.
Reason: Homologous organs have similar functions but are different in their structural details and origin.

Explanation

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

### Step 1: Understand the Assertion
- **Assertion**: Thorns and tendrils of Bougainvillea and Cucurbita represent homology.
- **Analysis**: Homologous structures are those that have a common evolutionary origin but may serve different functions. In this case, the thorns of Bougainvillea (which serve as a protective mechanism) and the tendrils of Cucurbita (which provide support) are both modifications of the stem. Thus, they share a common origin.

### Step 2: Understand the Reason
- **Reason**: Homologous organs have similar functions but are different in their structural details and origin.
- **Analysis**: This statement is incorrect. Homologous organs do not have similar functions; rather, they have different functions but share a common origin. The reason provided contradicts the definition of homologous structures.

### Step 3: Conclusion
- The assertion is true because thorns and tendrils are indeed homologous structures, having evolved from a common stem modification.
- The reason is false because it incorrectly states that homologous organs have similar functions.

### Final Answer
- The correct answer is that the assertion is true, but the reason is false.

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