What is gross primary productivity ? In what unit is it expressed ?

Explanation

**Step-by-Step Solution:**

1. **Definition of Gross Primary Productivity (GPP):**
- Gross Primary Productivity refers to the total amount of organic matter (biomass) produced by autotrophs, primarily green plants, through the process of photosynthesis. It represents the total energy captured by photosynthetic organisms in a given area over a specific time period.

2. **Components of the Definition:**
- **Total Organic Matter:** This includes all the carbohydrates, proteins, and other organic compounds synthesized by plants.
- **Synthesis by Producers:** Producers, or autotrophs, are organisms that can produce their own food using sunlight (in the case of photosynthesis) or chemical energy.
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