Gross primary productivity is the

Options

A. rate at which organic molecules are formed in a heterotroph
B. rate of consuming organic molecules by an autotroph
C. rate of storage of organic compounds in an autotroph
D. rate of formation of organic molecules by an autotroph

Answer

### Step-by-Step Solution:

1. **Understanding Primary Productivity**:
- Primary productivity refers to the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. It is an essential concept in ecology as it determines the energy available to the rest of the food chain.

2. **Differentiating Between Types of Productivity**:
- **Gross Primary Productivity (GPP)**: This is the total amount of organic matter produced by autotrophs (like plants) through photosynthesis in a given area over a specific time period.
- **Net Primary Productivity (NPP)**: This is the amount of organic matter that remains after autotrophs have used some of the energy for their own respiration. It is calculated as GPP minus the energy used in respiration.

3. **Identifying Autotrophs**:
- Autotrophs are organisms that can produce their own food from inorganic substances. In most ecosystems, this is primarily done by green plants through the process of photosynthesis.

4. **Defining Gross Primary Productivity**:
- GPP can be defined as the rate of production of organic matter (or organic molecules) by autotrophs. This production is primarily driven by the process of photosynthesis.

5. **Conclusion**:
- Therefore, Gross Primary Productivity (GPP) is the rate of formation of organic molecules by autotrophs through photosynthesis.

### Final Answer:
Gross Primary Productivity is the rate of formation of organic molecules by autotrophs.

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