Unloading of mineral ions occur at the fine vein endings through (A) _____ and (B) _____ sink cells.

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: The question asks about the unloading of mineral ions at the fine vein endings in plants. To answer this, we need to understand the concepts of "source" and "sink" in plant physiology.

2. **Defining Source and Sink**: In plants, a source is where substances (like minerals and nutrients) are produced or stored, while a sink is where these substances are utilized. The main sinks in plants include growing regions such as apical and lateral meristems, young leaves, developing fruits, seeds, and storage organs.

3. **Identifying the Process of Unloading**: The unloading of mineral ions at the fine vein endings occurs through two processes:
- **(A)** The first process is **diffusion**, which is a passive transport mechanism. In diffusion, substances move from an area of higher concentration to an area of lower concentration without the need for energy.
- **(B)** The second process is **active uptake** by sink cells. Active uptake requires energy, as it involves moving substances against their concentration gradient (from lower to higher concentration).

4. **Filling in the Blanks**: Based on the understanding of the processes involved in unloading mineral ions:
- (A) is **diffusion**
- (B) is **active uptake**

5. **Final Answer**: The complete statement is: "Unloading of mineral ions occur at the fine vein endings through (A) diffusion and (B) active uptake sink cells."

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