Define bioassay.

Explanation

**Step-by-Step Solution:**

1. **Definition of Bioassay**: Bioassay is a scientific method used to evaluate the effects of a substance on living organisms, particularly plants.

2. **Purpose of Bioassay**: The main purpose of a bioassay is to determine the biological activity of a substance, specifically its ability to induce a growth response in a living plant or its parts.

3. **Measurement of Growth Response**: In a bioassay, the growth response is quantified, which means measuring how much the substance affects the growth of the plant or its specific parts.

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