In amoeba and paramoecium, useful substances are distributed by a process called_________.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Organisms**: First, we need to recognize that both amoeba and paramecium are unicellular organisms. This means they consist of a single cell that performs all necessary life processes.

2. **Identifying the Process**: The question asks about the process by which useful substances are distributed within these organisms. In unicellular organisms, substances must move in and out of the cell to maintain homeostasis and support cellular functions.

3. **Explaining the Mechanism**: The primary mechanism for the distribution of substances in amoeba and paramecium is diffusion. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

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