The rate at which light energy is converted into chemical energy of organic molecules, is the ecosystem's
(a) net primary productivity
(b) net secondary productivity
(c) gross secondary productivity
(d) gross primary productivity

Options

A. net primary productivity
B. net secondary productivity
C. gross secondary productivity
D. gross primary productivity

Answer

To solve the question regarding the rate at which light energy is converted into chemical energy of organic molecules in an ecosystem, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terms**:
- We need to clarify what productivity means in an ecological context. Productivity refers to the rate of biomass production in an ecosystem.

2. **Differentiate Types of Productivity**:
- Productivity is divided into two main types:
- **Gross Primary Productivity (GPP)**: This is the total rate at which light energy is converted into chemical energy by photosynthesis. It represents the total organic matter produced.
- **Net Primary Productivity (NPP)**: This is the GPP minus the energy used by plants for respiration. It indicates the actual amount of energy available for consumption by herbivores and other organisms.

3. **Identify the Key Concept**:
- The question specifically asks about the rate at which light energy is converted into chemical energy of organic molecules. This definition aligns with the concept of Gross Primary Productivity (GPP).

4. **Eliminate Incorrect Options**:
- **Net Secondary Productivity**: This refers to the energy available to consumers after accounting for the energy used in respiration by primary consumers.
- **Gross Secondary Productivity**: This refers to the total energy assimilated by consumers, which is not relevant to the conversion of light energy.
- **Net Primary Productivity**: This is the energy available after respiration losses, which is not what the question is asking.

5. **Select the Correct Answer**:
- Since the question is about the conversion of light energy into chemical energy during photosynthesis, the correct answer is **(d) Gross Primary Productivity**.

### Final Answer:
(d) gross primary productivity