Mass or bulk flow of substance is called -

Options

A. Active transport
B. Translocation
C. Diffusion
D. Facilitated diffusion

Answer

**Step-by-Step Solution:**

1. **Understanding Mass or Bulk Flow**: The question is asking about the term used to describe the mass or bulk flow of substances in plants. Mass flow refers to the movement of a large quantity of substances in a unified manner.

2. **Identifying the Context**: In plants, mass flow is primarily observed in the phloem, where phloem sap moves from areas of high concentration (source) to areas of low concentration (sink). This is a critical process for transporting nutrients, especially sugars produced during photosynthesis.

3. **Defining Key Terms**:
- **Active Transport**: This is the movement of substances against their concentration gradient, requiring energy. It does not describe mass flow.
- **Translocation**: This is the correct term for the mass flow of substances in phloem. It describes the movement of nutrients from source to sink.
- **Diffusion**: This is the passive movement of substances from high to low concentration but does not involve mass flow over long distances.
- **Facilitated Diffusion**: This is a form of passive transport that requires specific carrier proteins but is not applicable to mass flow.

4. **Conclusion**: Based on the definitions and the context of the question, the term that describes the mass or bulk flow of substances in plants is **translocation**.

**Final Answer**: Translocation

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